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Lukasiewicz CJ, Vandiver KJ, Albert ED, Kirby BS, Jacobs RA. Assessing exogenous carbohydrate intake needed to optimize human endurance performance across sex: insights from modeling runners pursuing a sub-2-h marathon. J Appl Physiol (1985) 2024; 136:158-176. [PMID: 38059288 DOI: 10.1152/japplphysiol.00521.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Revised: 11/27/2023] [Accepted: 11/29/2023] [Indexed: 12/08/2023] Open
Abstract
Carbohydrate (CHO) availability sustains high metabolic demands during prolonged exercise. The adequacy of current CHO intake recommendations, 30-90 g·h-1 dependent on CHO mixture and tolerability, to support elite marathon performance is unclear. We sought to scrutinize the current upper limit recommendation for exogenous CHO intake to support modeled sub-2-h marathon (S2M) attempts across elite male and female runners. Male and female runners (n = 120 each) were modeled from published literature with reference characteristics necessary to complete a S2M (e.g., body mass and running economy). Completion of a S2M was considered across a range of respiratory exchange rates, with maximal starting skeletal muscle and liver glycogen content predicted for elite male and female runners. Modeled exogenous CHO bioavailability needed for male and female runners were 93 ± 26 and 108 ± 22 g·h-1, respectively (P < 0.0001, d = 0.61). Without exogenous CHO, males were modeled to deplete glycogen in 84 ± 7 min, females in 71 ± 5 min (P < 0.0001, d = 2.21) despite higher estimated CHO oxidation rates in males (5.1 ± 0.5 g·h-1) than females (4.4 ± 0.5 g·h-1; P < 0.0001, d = 1.47). Exogenous CHO intakes ≤ 90 g·h-1 are insufficient for 65% of modeled runners attempting a S2M. Current recommendations to support marathon performance appear inadequate for elite marathon runners but may be more suitable for male runners in pursuit of a S2M (56 of 120) than female runners (28 of 120).NEW & NOTEWORTHY This study scrutinizes the upper limit of exogenous carbohydrate (CHO) recommendations for elite male and female marathoners by modeling sex-specific needs across an extreme metabolic challenge lasting ∼2 h, a sub-2-h marathon. Contemporary nutritional guidelines to optimize marathon performance appear inadequate for most elite marathon runners but appear more appropriate for males over their female counterparts. Future research examining possible benefits of exogenous CHO intakes > 90 g·h-1 should prioritize female athlete study inclusion.
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Affiliation(s)
- Cole J Lukasiewicz
- Department of Human Physiology & Nutrition, College of Nursing and Health Sciences, University of Colorado Colorado Springs (UCCS), Colorado Springs, Colorado, United States
- William J. Hybl Sports Medicine and Performance Center, Colorado Springs, Colorado, United States
| | - Kayla J Vandiver
- Department of Human Physiology & Nutrition, College of Nursing and Health Sciences, University of Colorado Colorado Springs (UCCS), Colorado Springs, Colorado, United States
- William J. Hybl Sports Medicine and Performance Center, Colorado Springs, Colorado, United States
| | - Elizabeth D Albert
- Department of Human Physiology & Nutrition, College of Nursing and Health Sciences, University of Colorado Colorado Springs (UCCS), Colorado Springs, Colorado, United States
- William J. Hybl Sports Medicine and Performance Center, Colorado Springs, Colorado, United States
| | - Brett S Kirby
- Nike Sport Research Lab, Nike, Inc., Beaverton, Oregon, United States
| | - Robert A Jacobs
- Department of Human Physiology & Nutrition, College of Nursing and Health Sciences, University of Colorado Colorado Springs (UCCS), Colorado Springs, Colorado, United States
- William J. Hybl Sports Medicine and Performance Center, Colorado Springs, Colorado, United States
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German JS, Jacobs RA. Implications of capacity-limited, generative models for human vision. Behav Brain Sci 2023; 46:e391. [PMID: 38054373 DOI: 10.1017/s0140525x23001772] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/07/2023]
Abstract
Although discriminative deep neural networks are currently dominant in cognitive modeling, we suggest that capacity-limited, generative models are a promising avenue for future work. Generative models tend to learn both local and global features of stimuli and, when properly constrained, can learn componential representations and response biases found in people's behaviors.
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Affiliation(s)
- Joseph Scott German
- Department of Cognitive Science, University of California, San Diego, La Jolla, CA, USA
| | - Robert A Jacobs
- Department of Brain and Cognitive Sciences, University of Rochester, Rochester, NY, USA https://www2.bcs.rochester.edu/sites/jacobslab/people.html
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Walsh MA, Musci RV, Jacobs RA, Hamilton KL. A practical perspective on how to develop, implement, execute, and reproduce high-resolution respirometry experiments: The physiologist's guide to an Oroboros O2k. FASEB J 2023; 37:e23280. [PMID: 37899680 DOI: 10.1096/fj.202301644rr] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2023] [Revised: 09/29/2023] [Accepted: 10/13/2023] [Indexed: 10/31/2023]
Abstract
The development of high-resolution respirometry (HRR) has greatly expanded the analytical scope to study mitochondrial respiratory control relative to specific tissue/cell types across various metabolic states. Specifically, the Oroboros Oxygraph 2000 (O2k) is a common tool for measuring rates of mitochondrial respiration and is the focus of this perspective. The O2k platform is amenable for answering numerous bioenergetic questions. However, inherent variability with HRR-derived data, both within and amongst users, can impede progress in bioenergetics research. Therefore, we advocate for several vital considerations when planning and conducting O2k experiments to ultimately enhance transparency and reproducibility across laboratories. In this perspective, we offer guidance for best practices of mitochondrial preparation, protocol selection, and measures to increase reproducibility. The goal of this perspective is to propagate the use of the O2k, enhance reliability and validity for both new and experienced O2k users, and provide a reference for peer reviewers.
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Affiliation(s)
- Maureen A Walsh
- Health and Exercise Science Department, Colorado State University, Fort Collins, Colorado, USA
| | - Robert V Musci
- Health and Human Sciences Department, Loyola Marymount University, Los Angeles, California, USA
| | - Robert A Jacobs
- Department of Human Physiology and Nutrition, University of Colorado Colorado Springs (UCCS), Colorado Springs, Colorado, USA
- William J. Hybl Sports Medicine and Performance Center, Colorado Springs, Colorado, USA
| | - Karyn L Hamilton
- Health and Exercise Science Department, Colorado State University, Fort Collins, Colorado, USA
- Columbine Health Systems Center for Healthy Aging, Colorado State University, Fort Collins, Colorado, USA
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German JS, Cui G, Xu C, Jacobs RA. Rapid runtime learning by curating small datasets of high-quality items obtained from memory. PLoS Comput Biol 2023; 19:e1011445. [PMID: 37792896 PMCID: PMC10578607 DOI: 10.1371/journal.pcbi.1011445] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2022] [Revised: 10/16/2023] [Accepted: 08/19/2023] [Indexed: 10/06/2023] Open
Abstract
We propose the "runtime learning" hypothesis which states that people quickly learn to perform unfamiliar tasks as the tasks arise by using task-relevant instances of concepts stored in memory during mental training. To make learning rapid, the hypothesis claims that only a few class instances are used, but these instances are especially valuable for training. The paper motivates the hypothesis by describing related ideas from the cognitive science and machine learning literatures. Using computer simulation, we show that deep neural networks (DNNs) can learn effectively from small, curated training sets, and that valuable training items tend to lie toward the centers of data item clusters in an abstract feature space. In a series of three behavioral experiments, we show that people can also learn effectively from small, curated training sets. Critically, we find that participant reaction times and fitted drift rates are best accounted for by the confidences of DNNs trained on small datasets of highly valuable items. We conclude that the runtime learning hypothesis is a novel conjecture about the relationship between learning and memory with the potential for explaining a wide variety of cognitive phenomena.
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Affiliation(s)
- Joseph Scott German
- Institute for Psychology and Centre for Cognitive Science, Technical University of Darmstadt, Darmstadt, Germany
| | - Guofeng Cui
- Department of Computer Science, Rutgers University, Piscataway, New Jersey, United States of America
| | - Chenliang Xu
- Department of Computer Science, University of Rochester, Rochester, New York, United States of America
| | - Robert A. Jacobs
- Department of Brain and Cognitive Sciences, University of Rochester, Rochester, New York, United States of America
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5
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Aboouf MA, Guscetti F, von Büren N, Armbruster J, Ademi H, Ruetten M, Meléndez-Rodríguez F, Rülicke T, Seymer A, Jacobs RA, Schneider Gasser EM, Aragones J, Neumann D, Gassmann M, Thiersch M. Erythropoietin receptor regulates tumor mitochondrial biogenesis through iNOS and pAKT. Front Oncol 2022; 12:976961. [PMID: 36052260 PMCID: PMC9425774 DOI: 10.3389/fonc.2022.976961] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Accepted: 07/18/2022] [Indexed: 11/13/2022] Open
Abstract
Erythropoietin receptor (EPOR) is widely expressed in healthy and malignant tissues. In certain malignancies, EPOR stimulates tumor growth. In healthy tissues, EPOR controls processes other than erythropoiesis, including mitochondrial metabolism. We hypothesized that EPOR also controls the mitochondrial metabolism in cancer cells. To test this hypothesis, we generated EPOR-knockdown cancer cells to grow tumor xenografts in mice and analyzed tumor cellular respiration via high-resolution respirometry. Furthermore, we analyzed cellular respiratory control, mitochondrial content, and regulators of mitochondrial biogenesis in vivo and in vitro in different cancer cell lines. Our results show that EPOR controls tumor growth and mitochondrial biogenesis in tumors by controlling the levels of both, pAKT and inducible NO synthase (iNOS). Furthermore, we observed that the expression of EPOR is associated with the expression of the mitochondrial marker VDAC1 in tissue arrays of lung cancer patients, suggesting that EPOR indeed helps to regulate mitochondrial biogenesis in tumors of cancer patients. Thus, our data imply that EPOR not only stimulates tumor growth but also regulates tumor metabolism and is a target for direct intervention against progression.
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Affiliation(s)
- Mostafa A. Aboouf
- Institute of Veterinary Physiology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
- Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich, Zurich, Switzerland
- Center for Clinical Studies, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
- Department of Biochemistry, Faculty of Pharmacy, Ain Shams University, Cairo, Egypt
| | - Franco Guscetti
- Institute of Veterinary Pathology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
| | - Nadine von Büren
- Institute of Veterinary Physiology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
- Center for Clinical Studies, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
| | - Julia Armbruster
- Institute of Veterinary Physiology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
- Center for Clinical Studies, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
| | - Hyrije Ademi
- Institute of Veterinary Physiology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
- Center for Clinical Studies, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
| | - Maja Ruetten
- PathoVet AG, Pathology Diagnostic Laboratory, Tagelswangen, Switzerland
| | | | - Thomas Rülicke
- Department of Biomedical Sciences, University of Veterinary Medicine Vienna, Vienna, Austria
| | - Alexander Seymer
- Department for Sociology and Social Geography, Paris Lodron University of Salzburg (PLUS), Salzburg, Austria
| | - Robert A. Jacobs
- Department of Human Physiology & Nutrition, University of Colorado Colorado Springs (UCCS), Colorado Springs, CO, United States
| | - Edith M. Schneider Gasser
- Institute of Veterinary Physiology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
- Center of Neuroscience Zurich (ZNZ), University of Zurich, Zurich, Switzerland
| | - Julian Aragones
- Hospital Universitario Santa Cristina, Autonomous University of Madrid, Madrid, Spain
| | - Drorit Neumann
- Department of Cell and Developmental Biology, Sackler Faculty of Medicine, Tel Aviv University, Tel-Aviv, Israel
| | - Max Gassmann
- Institute of Veterinary Physiology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
- Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich, Zurich, Switzerland
| | - Markus Thiersch
- Institute of Veterinary Physiology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
- Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich, Zurich, Switzerland
- Center for Clinical Studies, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
- *Correspondence: Markus Thiersch,
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Sims CR, Lerch RA, Tarduno JA, Jacobs RA. Conceptual knowledge shapes visual working memory for complex visual information. Sci Rep 2022; 12:8088. [PMID: 35577845 PMCID: PMC9110428 DOI: 10.1038/s41598-022-12137-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Accepted: 05/05/2022] [Indexed: 11/28/2022] Open
Abstract
Human visual working memory (VWM) is a memory store people use to maintain the visual features of objects and scenes. Although it is obvious that bottom-up information influences VWM, the extent to which top-down conceptual information influences VWM is largely unknown. We report an experiment in which groups of participants were trained in one of two different categories of geologic faults (left/right lateral, or normal/reverse faults), or received no category training. Following training, participants performed a visual change detection task in which category knowledge was irrelevant to the task. Participants were more likely to detect a change in geologic scenes when the changes crossed a trained categorical distinction (e.g., the left/right lateral fault boundary), compared to within-category changes. In addition, participants trained to distinguish left/right lateral faults were more likely to detect changes when the scenes were mirror images along the left/right dimension. Similarly, participants trained to distinguish normal/reverse faults were more likely to detect changes when scenes were mirror images along the normal/reverse dimension. Our results provide direct empirical evidence that conceptual knowledge influences VWM performance for complex visual information. An implication of our results is that cognitive scientists may need to reconceptualize VWM so that it is closer to "conceptual short-term memory".
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Affiliation(s)
- Chris R Sims
- Department of Cognitive Science, Rensselaer Polytechnic Institute, Troy, NY, 12180, USA
| | - Rachel A Lerch
- Department of Psychology, University of Texas at Austin, Austin, TX, 78712, USA
| | - John A Tarduno
- Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY, 14627, USA
| | - Robert A Jacobs
- Department of Brain and Cognitive Sciences, University of Rochester, Rochester, NY, 14627, USA.
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Wu MH, Anderson AJ, Jacobs RA, Raizada RDS. Analogy-Related Information Can Be Accessed by Simple Addition and Subtraction of fMRI Activation Patterns, Without Participants Performing any Analogy Task. Neurobiol Lang (Camb) 2022; 3:1-17. [PMID: 37215331 PMCID: PMC10158578 DOI: 10.1162/nol_a_00045] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/02/2020] [Accepted: 06/15/2021] [Indexed: 05/24/2023]
Abstract
Analogical reasoning, for example, inferring that teacher is to chalk as mechanic is to wrench, plays a fundamental role in human cognition. However, whether brain activity patterns of individual words are encoded in a way that could facilitate analogical reasoning is unclear. Recent advances in computational linguistics have shown that information about analogical problems can be accessed by simple addition and subtraction of word embeddings (e.g., wrench = mechanic + chalk - teacher). Critically, this property emerges in artificial neural networks that were not trained to produce analogies but instead were trained to produce general-purpose semantic representations. Here, we test whether such emergent property can be observed in representations in human brains, as well as in artificial neural networks. fMRI activation patterns were recorded while participants viewed isolated words but did not perform analogical reasoning tasks. Analogy relations were constructed from word pairs that were categorically or thematically related, and we tested whether the predicted fMRI pattern calculated with simple arithmetic was more correlated with the pattern of the target word than other words. We observed that the predicted fMRI patterns contain information about not only the identity of the target word but also its category and theme (e.g., teaching-related). In summary, this study demonstrated that information about analogy questions can be reliably accessed with the addition and subtraction of fMRI patterns, and that, similar to word embeddings, this property holds for task-general patterns elicited when participants were not explicitly told to perform analogical reasoning.
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Affiliation(s)
- Meng-Huan Wu
- Department of Brain & Cognitive Sciences, University of Rochester, Rochester, New York, USA
| | - Andrew J. Anderson
- Department of Neuroscience, University of Rochester, Rochester, New York, USA
- Del Monte Institute for Neuroscience, University of Rochester, Rochester, New York, USA
| | - Robert A. Jacobs
- Department of Brain & Cognitive Sciences, University of Rochester, Rochester, New York, USA
| | - Rajeev D. S. Raizada
- Department of Brain & Cognitive Sciences, University of Rochester, Rochester, New York, USA
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8
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Jacobs RA, Aboouf MA, Koester-Hegmann C, Muttathukunnel P, Laouafa S, Arias-Reyes C, Thiersch M, Soliz J, Gassmann M, Schneider Gasser EM. Erythropoietin promotes hippocampal mitochondrial function and enhances cognition in mice. Commun Biol 2021; 4:938. [PMID: 34354241 PMCID: PMC8342552 DOI: 10.1038/s42003-021-02465-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2020] [Accepted: 07/19/2021] [Indexed: 11/22/2022] Open
Abstract
Erythropoietin (EPO) improves neuronal mitochondrial function and cognition in adults after brain injury and in those afflicted by psychiatric disorders. However, the influence of EPO on mitochondria and cognition during development remains unexplored. We previously observed that EPO stimulates hippocampal-specific neuronal maturation and synaptogenesis early in postnatal development in mice. Here we show that EPO promotes mitochondrial respiration in developing postnatal hippocampus by increasing mitochondrial content and enhancing cellular respiratory potential. Ultrastructurally, mitochondria profiles and total vesicle content were greater in presynaptic axon terminals, suggesting that EPO enhances oxidative metabolism and synaptic transmission capabilities. Behavioural tests of hippocampus-dependent memory at early adulthood, showed that EPO improves spatial and short-term memory. Collectively, we identify a role for EPO in the murine postnatal hippocampus by promoting mitochondrial function throughout early postnatal development, which corresponds to enhanced cognition by early adulthood. Robert Jacobs, Mostafa Aboouf, et al. examined the effect of erythropoietin (EPO) in hippocampal mitochondrial function and memory in two mouse models: one overexpressing EPO in the brain, and juvenile mice treated during three days with a high dose of intraperitoneal EPO. Their results suggest that erythropoietin in the neonatal brain may impact spatial memory by increasing mitochondrial content.
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Affiliation(s)
- Robert A Jacobs
- Institute of Veterinary Physiology, Vetsuisse-Faculty, University of Zurich, Zurich, Switzerland.,Department of Human Physiology & Nutrition, University of Colorado, Colorado Springs, CO, USA
| | - Mostafa A Aboouf
- Institute of Veterinary Physiology, Vetsuisse-Faculty, University of Zurich, Zurich, Switzerland.,Zurich Center for Integrative Human Physiology (ZIPH), University of Zurich, Zurich, Switzerland.,Department of Biochemistry, Faculty of Pharmacy, Ain Shams University, Cairo, Egypt
| | - Christina Koester-Hegmann
- Institute of Veterinary Physiology, Vetsuisse-Faculty, University of Zurich, Zurich, Switzerland.,Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland
| | - Paola Muttathukunnel
- Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland.,Center for Neuroscience Zurich (ZNZ), Zurich, Switzerland
| | - Sofien Laouafa
- Faculty of Medicine, Centre Hospitalier Universitaire de Québec (CHUQ), Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec, QC, Canada
| | - Christian Arias-Reyes
- Faculty of Medicine, Centre Hospitalier Universitaire de Québec (CHUQ), Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec, QC, Canada
| | - Markus Thiersch
- Institute of Veterinary Physiology, Vetsuisse-Faculty, University of Zurich, Zurich, Switzerland.,Zurich Center for Integrative Human Physiology (ZIPH), University of Zurich, Zurich, Switzerland
| | - Jorge Soliz
- Faculty of Medicine, Centre Hospitalier Universitaire de Québec (CHUQ), Institut Universitaire de Cardiologie et de Pneumologie de Québec, Université Laval, Québec, QC, Canada
| | - Max Gassmann
- Institute of Veterinary Physiology, Vetsuisse-Faculty, University of Zurich, Zurich, Switzerland.,Zurich Center for Integrative Human Physiology (ZIPH), University of Zurich, Zurich, Switzerland
| | - Edith M Schneider Gasser
- Institute of Veterinary Physiology, Vetsuisse-Faculty, University of Zurich, Zurich, Switzerland. .,Institute of Pharmacology and Toxicology, University of Zurich, Zurich, Switzerland. .,Center for Neuroscience Zurich (ZNZ), Zurich, Switzerland.
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Bates CJ, Jacobs RA. Optimal attentional allocation in the presence of capacity constraints in uncued and cued visual search. J Vis 2021; 21:3. [PMID: 33944906 PMCID: PMC8107488 DOI: 10.1167/jov.21.5.3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Accepted: 03/09/2021] [Indexed: 11/24/2022] Open
Abstract
The vision sciences literature contains a large diversity of experimental and theoretical approaches to the study of visual attention. We argue that this diversity arises, at least in part, from the field's inability to unify differing theoretical perspectives. In particular, the field has been hindered by a lack of a principled formal framework for simultaneously thinking about both optimal attentional processing and capacity-limited attentional processing, where capacity is limited in a general, task-independent manner. Here, we supply such a framework based on rate-distortion theory (RDT) and optimal lossy compression. Our approach defines Bayes-optimal performance when an upper limit on information processing rate is imposed. In this article, we compare Bayesian and RDT accounts in both uncued and cued visual search tasks. We start by highlighting a typical shortcoming of unlimited-capacity Bayesian models that is not shared by RDT models, namely, that they often overestimate task performance when information-processing demands are increased. Next, we reexamine data from two cued-search experiments that have previously been modeled as the result of unlimited-capacity Bayesian inference and demonstrate that they can just as easily be explained as the result of optimal lossy compression. To model cued visual search, we introduce the concept of a "conditional communication channel." This simple extension generalizes the lossy-compression framework such that it can, in principle, predict optimal attentional-shift behavior in any kind of perceptual task, even when inputs to the model are raw sensory data such as image pixels. To demonstrate this idea's viability, we compare our idealized model of cued search, which operates on a simplified abstraction of the stimulus, to a deep neural network version that performs approximately optimal lossy compression on the real (pixel-level) experimental stimuli.
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Affiliation(s)
| | - Robert A Jacobs
- Department of Brain and Cognitive Sciences, University of Rochester, Rochester, NY, USA
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10
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Jacobs RA, Lundby C. Contextualizing the biological relevance of standardized high-resolution respirometry to assess mitochondrial function in permeabilized human skeletal muscle. Acta Physiol (Oxf) 2021; 231:e13625. [PMID: 33570804 PMCID: PMC8047922 DOI: 10.1111/apha.13625] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2020] [Revised: 02/08/2021] [Accepted: 02/09/2021] [Indexed: 12/16/2022]
Abstract
Aim This study sought to provide a statistically robust reference for measures of mitochondrial function from standardized high‐resolution respirometry with permeabilized human skeletal muscle (ex vivo), compare analogous values obtained via indirect calorimetry, arterial‐venous O2 differences and 31P magnetic resonance spectroscopy (in vivo) and attempt to resolve differences across complementary methodologies as necessary. Methods Data derived from 831 study participants across research published throughout March 2009 to November 2019 were amassed to examine the biological relevance of ex vivo assessments under standard conditions, ie physiological temperatures of 37°C and respiratory chamber oxygen concentrations of ~250 to 500 μmol/L. Results Standard ex vivo‐derived measures are lower (Z ≥ 3.01, P ≤ .0258) en masse than corresponding in vivo‐derived values. Correcting respiratory values to account for mitochondrial temperatures 10°C higher than skeletal muscle temperatures at maximal exercise (~50°C): (i) transforms data to resemble (Z ≤ 0.8, P > .9999) analogous yet context‐specific in vivo measures, eg data collected during maximal 1‐leg knee extension exercise; and (ii) supports the position that maximal skeletal muscle respiratory rates exceed (Z ≥ 13.2, P < .0001) those achieved during maximal whole‐body exercise, e.g. maximal cycling efforts. Conclusion This study outlines and demonstrates necessary considerations when actualizing the biological relevance of human skeletal muscle respiratory control, metabolic flexibility and bioenergetics from standard ex vivo‐derived assessments using permeabilized human muscle. These findings detail how cross‐procedural comparisons of human skeletal muscle mitochondrial function may be collectively scrutinized in their relationship to human health and lifespan.
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Affiliation(s)
- Robert A. Jacobs
- Department of Human Physiology & Nutrition University of Colorado Colorado Springs (UCCS) Colorado Springs CO USA
| | - Carsten Lundby
- Innland University of Applied Sciences Lillehammer Norway
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Subudhi AW, Batterson PM, Hubbell ED, Jacobs RA. Reliability Of Cycling Time Trials Performed At Maximal And Submaximal Intensities. Med Sci Sports Exerc 2020. [DOI: 10.1249/01.mss.0000670436.51071.0e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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12
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Abstract
Efficient data compression is essential for capacity-limited systems, such as biological perception and perceptual memory. We hypothesize that the need for efficient compression shapes biological systems in many of the same ways that it shapes engineered systems. If true, then the tools that engineers use to analyze and design systems, namely rate-distortion theory (RDT), can profitably be used to understand human perception and memory. The first portion of this article discusses how three general principles for efficient data compression provide accounts for many important behavioral phenomena and experimental results. We also discuss how these principles are embodied in RDT. The second portion notes that exact RDT methods are computationally feasible only in low-dimensional stimulus spaces. To date, researchers have used deep neural networks to approximately implement RDT in high-dimensional spaces, but these implementations have been limited to tasks in which the sole goal is compression with respect to reconstruction error. Here, we introduce a new deep neural network architecture that approximately implements RDT. An important property of our architecture is that it is trained "end-to-end," operating on raw perceptual input (e.g., pixel values) rather than intermediate levels of abstraction, as is the case with most psychological models. The article's final portion conjectures on how efficient compression can occur in memory over time, thereby providing motivations for multiple memory systems operating at different time scales, and on how efficient compression may explain some attentional phenomena such as RTs in visual search. (PsycInfo Database Record (c) 2020 APA, all rights reserved).
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Soliz J, Arias-Reyes C, Laouafs S, Jacobs RA, Schneider Gasser EM. Cerebral erythropoietin increases the hippocampal mitochondrial respiration during the postnatal development. FASEB J 2020. [DOI: 10.1096/fasebj.2020.34.s1.04014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | | | | | - Edith M. Schneider Gasser
- Institute of Veterinary Physiology Vetsuisse-Faculty University of Zurich Winterthurerstrasse 260, and Center for Neuroscience Zurich (ZNZ) Zurich Switzerland
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Trotter CE, Tourula E, Pizzey FK, Batterson PM, Jacobs RA, Pearson J. High‐intensity interval exercise reduces tolerance to a simulated haemorrhagic challenge in heat‐stressed individuals. Exp Physiol 2020; 106:212-221. [DOI: 10.1113/ep088377] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2019] [Accepted: 01/28/2020] [Indexed: 11/08/2022]
Affiliation(s)
- Claire E. Trotter
- Department of Human Physiology and Nutrition University of Colorado at Colorado Springs Colorado Springs CO USA
- Department of Applied Physiology and Wellness Southern Methodist University Dallas TX USA
| | - Erica Tourula
- Department of Human Physiology and Nutrition University of Colorado at Colorado Springs Colorado Springs CO USA
| | - Faith K. Pizzey
- Department of Human Physiology and Nutrition University of Colorado at Colorado Springs Colorado Springs CO USA
- School of Human Movement and Nutrition Sciences The University of Queensland Brisbane Australia
| | - Philip M. Batterson
- Department of Human Physiology and Nutrition University of Colorado at Colorado Springs Colorado Springs CO USA
- College of Biological and Population Health Sciences Oregon State University Corvallis OR USA
| | - Robert A. Jacobs
- Department of Human Physiology and Nutrition University of Colorado at Colorado Springs Colorado Springs CO USA
| | - James Pearson
- Department of Human Physiology and Nutrition University of Colorado at Colorado Springs Colorado Springs CO USA
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15
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German JS, Jacobs RA. Can machine learning account for human visual object shape similarity judgments? Vision Res 2020; 167:87-99. [PMID: 31972448 DOI: 10.1016/j.visres.2019.12.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Revised: 10/22/2019] [Accepted: 12/12/2019] [Indexed: 11/27/2022]
Abstract
We describe and analyze the performance of metric learning systems, including deep neural networks (DNNs), on a new dataset of human visual object shape similarity judgments of naturalistic, part-based objects known as "Fribbles". In contrast to previous studies which asked participants to judge similarity when objects or scenes were rendered from a single viewpoint, we rendered Fribbles from multiple viewpoints and asked participants to judge shape similarity in a viewpoint-invariant manner. Metrics trained using pixel-based or DNN-based representations fail to explain our experimental data, but a metric trained with a viewpoint-invariant, part-based representation produces a good fit. We also find that although neural networks can learn to extract the part-based representation-and therefore should be capable of learning to model our data-networks trained with a "triplet loss" function based on similarity judgments do not perform well. We analyze this failure, providing a mathematical description of the relationship between the metric learning objective function and the triplet loss function. The poor performance of neural networks appears to be due to the nonconvexity of the optimization problem in network weight space. We conclude that viewpoint insensitivity is a critical aspect of human visual shape perception, and that neural network and other machine learning methods will need to learn viewpoint-insensitive representations in order to account for people's visual object shape similarity judgments.
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Affiliation(s)
- Joseph Scott German
- Department of Brain and Cognitive Sciences, University of Rochester, Rochester, NY 14627, United States.
| | - Robert A Jacobs
- Department of Brain and Cognitive Sciences, University of Rochester, Rochester, NY 14627, United States.
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16
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Batterson PM, Norton MR, Hetz SE, Rohilla S, Lindsay KG, Subudhi AW, Jacobs RA. Improving biologic predictors of cycling endurance performance with near-infrared spectroscopy derived measures of skeletal muscle respiration: E pluribus unum. Physiol Rep 2020; 8:e14342. [PMID: 31960629 PMCID: PMC6971325 DOI: 10.14814/phy2.14342] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The study aim was to compare the predictive validity of the often referenced traditional model of human endurance performance (i.e. oxygen consumption, VO2 , or power at maximal effort, fatigue threshold values, and indices of exercise efficiency) versus measures of skeletal muscle oxidative potential in relation to endurance cycling performance. We hypothesized that skeletal muscle oxidative potential would more completely explain endurance performance than the traditional model, which has never been collectively verified with cycling. Accordingly, we obtained nine measures of VO2 or power at maximal efforts, 20 measures reflective of various fatigue threshold values, 14 indices of cycling efficiency, and near-infrared spectroscopy-derived measures reflecting in vivo skeletal muscle oxidative potential. Forward regression modeling identified variable combinations that best explained 25-km time trial time-to-completion (TTC) across a group of trained male participants (n = 24). The time constant for skeletal muscle oxygen consumption recovery, a validated measure of maximal skeletal muscle respiration, explained 92.7% of TTC variance by itself (Adj R2 = .927, F = 294.2, SEE = 71.2, p < .001). Alternatively, the best complete traditional model of performance, including VO2max (L·min-1 ), %VO2max determined by the ventilatory equivalents method, and cycling economy at 50 W, only explained 76.2% of TTC variance (Adj R2 = .762, F = 25.6, SEE = 128.7, p < .001). These results confirm our hypothesis by demonstrating that maximal rates of skeletal muscle respiration more completely explain cycling endurance performance than even the best combination of traditional variables long postulated to predict human endurance performance.
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Affiliation(s)
- Philip M. Batterson
- Department of BiologyUniversity of Colorado Colorado SpringsColorado SpringsCOUSA
| | - Michael R. Norton
- Department of BiologyUniversity of Colorado Colorado SpringsColorado SpringsCOUSA
| | - Sarah E. Hetz
- Department of BiologyUniversity of Colorado Colorado SpringsColorado SpringsCOUSA
| | - Sachi Rohilla
- Department of BiologyUniversity of Colorado Colorado SpringsColorado SpringsCOUSA
| | - Keston G. Lindsay
- Department of Human Physiology and NutritionUniversity of Colorado Colorado SpringsColorado SpringsCOUSA
- Department of Health SciencesUniversity of Colorado Colorado SpringsColorado SpringsCOUSA
| | - Andrew W. Subudhi
- Department of BiologyUniversity of Colorado Colorado SpringsColorado SpringsCOUSA
- Department of Human Physiology and NutritionUniversity of Colorado Colorado SpringsColorado SpringsCOUSA
| | - Robert A. Jacobs
- Department of BiologyUniversity of Colorado Colorado SpringsColorado SpringsCOUSA
- Department of Human Physiology and NutritionUniversity of Colorado Colorado SpringsColorado SpringsCOUSA
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17
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Chung S, Nelson MD, Hamaoka T, Jacobs RA, Pearson J, Subudhi AW, Jenkins NT, Bartlett MF, Fitzgerald LF, Miehm JD, Kent JA, Lucero AA, Rowlands DS, Stoner L, McCully KK, Call J, Rodriguez-Miguelez P, Harris RA, Porcelli S, Rasica L, Marzorati M, Quaresima V, Ryan TE, Vernillo G, Millet GP, Malatesta D, Millet GY, Zuo L, Chuang CC. Commentaries on Viewpoint: Principles, insights, and potential pitfalls of the noninvasive determination of muscle oxidative capacity by near-infrared spectroscopy. J Appl Physiol (1985) 2019; 124:249-255. [PMID: 29364790 DOI: 10.1152/japplphysiol.00857.2017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Affiliation(s)
| | | | | | | | | | | | | | | | | | | | | | | | | | - Lee Stoner
- Massey University,University of North Carolina at Chapel Hill
| | | | | | | | | | | | - Letizia Rasica
- National Research Council, Italy,University of Milan, Italy
| | | | | | | | | | | | | | | | - Li Zuo
- The Ohio State University College of Medicine
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18
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Abstract
Although real-world environments are often multisensory, visual scientists typically study visual learning in unisensory environments containing visual signals only. Here, we use deep or artificial neural networks to address the question, Can multisensory training aid visual learning? We examine a network's internal representations of objects based on visual signals in two conditions: (a) when the network is initially trained with both visual and haptic signals, and (b) when it is initially trained with visual signals only. Our results demonstrate that a network trained in a visual-haptic environment (in which visual, but not haptic, signals are orientation-dependent) tends to learn visual representations containing useful abstractions, such as the categorical structure of objects, and also learns representations that are less sensitive to imaging parameters, such as viewpoint or orientation, that are irrelevant for object recognition or classification tasks. We conclude that researchers studying perceptual learning in vision-only contexts may be overestimating the difficulties associated with important perceptual learning problems. Although multisensory perception has its own challenges, perceptual learning can become easier when it is considered in a multisensory setting.
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Affiliation(s)
- Robert A Jacobs
- Department of Brain and Cognitive Sciences, University of Rochester, Rochester, NY, USA
| | - Chenliang Xu
- Department of Computer Science, University of Rochester, Rochester, NY, USA
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19
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Bates CJ, Lerch RA, Sims CR, Jacobs RA. Adaptive allocation of human visual working memory capacity during statistical and categorical learning. J Vis 2019; 19:11. [PMID: 30802280 DOI: 10.1167/19.2.11] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Human brains are finite, and thus have bounded capacity. An efficient strategy for a capacity-limited agent is to continuously adapt by dynamically reallocating capacity in a task-dependent manner. Here we study this strategy in the context of visual working memory (VWM). People use their VWM stores to remember visual information over seconds or minutes. However, their memory performances are often error-prone, presumably due to VWM capacity limits. We hypothesize that people attempt to be flexible and robust by strategically reallocating their limited VWM capacity based on two factors: (a) the statistical regularities (e.g., stimulus feature means and variances) of the to-be-remembered items, and (b) the requirements of the task that they are attempting to perform. The latter specifies, for example, which types of errors are costly versus irrelevant for task performance. These hypotheses are formalized within a normative computational modeling framework based on rate-distortion theory, an extension of conventional Bayesian approaches that uses information theory to study rate-limited (or capacity-limited) processes. Using images of plants that are naturalistic and precisely controlled, we carried out two sets of experiments. Experiment 1 found that when a stimulus dimension (the widths of plants' leaves) was assigned a distribution, subjects adapted their VWM performances based on this distribution. Experiment 2 found that when one stimulus dimension (e.g., leaf width) was relevant for distinguishing plant categories but another dimension (leaf angle) was irrelevant, subjects' responses in a memory task became relatively more sensitive to the relevant stimulus dimension. Together, these results illustrate the task-dependent robustness of VWM, thereby highlighting the dependence of memory on learning.
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Affiliation(s)
- Christopher J Bates
- Department of Brain & Cognitive Sciences, University of Rochester, Rochester, NY, USA
| | - Rachel A Lerch
- Cognitive Science Department, Rensselaer Polytechnic Institute, Troy, NY, USA
| | - Chris R Sims
- Cognitive Science Department, Rensselaer Polytechnic Institute, Troy, NY, USA
| | - Robert A Jacobs
- Department of Brain & Cognitive Sciences, University of Rochester, Rochester, NY, USA
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20
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Batterson PM, Norton MR, Hetz SE, Rohilla S, Lindsay K, Subudhi AW, Jacobs RA. Redefining Physiologic Predictors of Endurance Performance with Measures of Skeletal Muscle Oxygenation: E pluribus unum. Med Sci Sports Exerc 2019. [DOI: 10.1249/01.mss.0000560724.81978.40] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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21
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Trotter CE, Pizzey FK, Batterson PM, Jacobs RA, Pearson J. High intensity interval exercise reduces tolerance to a simulated hemorrhagic challenge relative to steady state exercise in heat stressed individuals. FASEB J 2019. [DOI: 10.1096/fasebj.2019.33.1_supplement.838.29] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Claire E Trotter
- BiologyUniversity of Colorado Colorado SpringsColorado SpringsCO
- Department of Applied Physiology and WellnessSouthern Methodist UniversityDallasTX
| | - Faith K Pizzey
- BiologyUniversity of Colorado Colorado SpringsColorado SpringsCO
| | | | - Robert A Jacobs
- BiologyUniversity of Colorado Colorado SpringsColorado SpringsCO
| | - James Pearson
- BiologyUniversity of Colorado Colorado SpringsColorado SpringsCO
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22
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Williams KA, Bell K, Jacobs RA, Subudhi AW. Supplemental Oxygen Does Not Influence Self-selected Work Rate at Moderate Altitude. Med Sci Sports Exerc 2018; 51:575-581. [PMID: 30299413 DOI: 10.1249/mss.0000000000001801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
INTRODUCTION It is well known that supplemental oxygen can increase aerobic power output during high-intensity and/or maximal efforts at moderate altitude, yet the effects on self-selected work rate during lower-intensity, submaximal exercise are unknown. We reasoned that if the degree of arterial oxygen saturation (SaO2) influences teleoanticipatory regulation of power output, supplemental oxygen given at moderate altitude would increase average power output during exercise performed at self-selected work rates corresponding to RPE 9 (very light) and 13 (somewhat hard). METHODS Twenty-three subjects (17 males, 6 females) completed one familiarization [fraction of inspired O2 (FIO2) = 0.209] and two blinded, experimental trials (FIO2 = 0.209 and FIO2 = 0.267). In each trial, subjects self-regulated their work rate on a cycle ergometer to maintain RPE 9 for 5 min and RPE 13 for 10 min, before performing an incremental step test to exhaustion (25 W·min). Oxygen consumption (V˙O2) and SaO2 via pulse oximetry (SpO2) were continuously monitored. Subjects were asked to guess the experimental condition after each stage of the protocol. RESULTS Supplemental oxygen increased SpO2 throughout exercise (~4%; P < 0.001) and was associated with greater peak power output (4% ± 4%; P < 0.001) and V˙O2 (5% ± 10%; P = 0.010) during the incremental test, but did not increase average power output selected during exercise at RPE 9 (P = 0.235) or 13 (P = 0.992). Subjects were unable to perceive the difference in FIO2 at any stage (P > 0.14). CONCLUSIONS Small increases in inspired oxygen concentration at moderate altitude are imperceptible and do not appear to influence selection of submaximal work rates at RPE ≤ 13.
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Affiliation(s)
- Kirsten A Williams
- University of Colorado Colorado Springs, Department of Biology, Colorado Springs, CO
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23
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Trotter CE, Pizzey FK, Batterson PM, Jacobs RA, Pearson J. Small reductions in skin temperature after onset of a simulated hemorrhagic challenge improve tolerance in exercise heat-stressed individuals. Am J Physiol Regul Integr Comp Physiol 2018; 315:R539-R546. [DOI: 10.1152/ajpregu.00182.2018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We investigated whether small reductions in skin temperature 60 s after the onset of a simulated hemorrhagic challenge would improve tolerance to lower body negative pressure (LBNP) after exercise heat stress. Eleven healthy subjects completed two trials (High and Reduced). Subjects cycled at ~55% maximal oxygen uptake wearing a warm water-perfused suit until core temperatures increased by ~1.2°C before lying supine and undergoing LBNP to presyncope. LBNP tolerance was quantified as cumulative stress index (CSI; product of each LBNP level multiplied by time; mmHg·min). Skin temperature was similarly elevated from baseline before LBNP and remained elevated 60 s after the onset of LBNP in both High (37.72 ± 0.52°C) and Reduced (37.95 ± 0.54°C) trials (both P < 0.0001). At 60%CSI skin temperature remained elevated in the High trial (37.51 ± 0.56°C) but was reduced to 34.97 ± 0.72°C by the water-perfused suit in the Reduced trial ( P < 0.0001 between trials). Cutaneous vascular conductance was not different between trials [High: 1.57 ± 0.43 vs. Reduced: 1.39 ± 0.38 arbitrary units (AU)/mmHg; P = 0.367] before LBNP but decreased to 0.67 ± 0.19 AU/mmHg at 60%CSI in the Reduced trial while remaining unchanged in the High trial ( P = 0.002 between trials). CSI was higher in the Reduced (695 ± 386 mmHg·min) relative to the High (441 ± 290 mmHg·min; P = 0.023) trial. Mean arterial pressure was not different between trials at presyncope (High: 62 ± 10 vs. Reduced: 62 ± 9 mmHg; P = 0.958). Small reductions in skin temperature after the onset of a simulated hemorrhagic challenge improve LBNP tolerance after exercise heat stress. This may have important implications regarding treatment of an exercise heat-stressed individual (e.g., soldier) who has experienced a hemorrhagic injury.
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Affiliation(s)
- Claire E. Trotter
- Department of Biology, University of Colorado at Colorado Springs, Colorado Springs, Colorado
| | - Faith K. Pizzey
- Department of Biology, University of Colorado at Colorado Springs, Colorado Springs, Colorado
| | - Philip M. Batterson
- Department of Biology, University of Colorado at Colorado Springs, Colorado Springs, Colorado
| | - Robert A. Jacobs
- Department of Biology, University of Colorado at Colorado Springs, Colorado Springs, Colorado
| | - James Pearson
- Department of Biology, University of Colorado at Colorado Springs, Colorado Springs, Colorado
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24
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Chen Q, Garcea FE, Jacobs RA, Mahon BZ. Abstract Representations of Object-Directed Action in the Left Inferior Parietal Lobule. Cereb Cortex 2018; 28:2162-2174. [PMID: 28605410 PMCID: PMC6019004 DOI: 10.1093/cercor/bhx120] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2016] [Revised: 03/28/2017] [Indexed: 11/14/2022] Open
Abstract
Prior neuroimaging and neuropsychological research indicates that the left inferior parietal lobule in the human brain is a critical substrate for representing object manipulation knowledge. In the present functional MRI study we used multivoxel pattern analyses to test whether action similarity among objects can be decoded in the inferior parietal lobule independent of the task applied to objects (identification or pantomime) and stimulus format in which stimuli are presented (pictures or printed words). Participants pantomimed the use of objects, cued by printed words, or identified pictures of objects. Classifiers were trained and tested across task (e.g., training data: pantomime; testing data: identification), stimulus format (e.g., training data: word format; testing format: picture) and specific objects (e.g., training data: scissors vs. corkscrew; testing data: pliers vs. screwdriver). The only brain region in which action relations among objects could be decoded across task, stimulus format and objects was the inferior parietal lobule. By contrast, medial aspects of the ventral surface of the left temporal lobe represented object function, albeit not at the same level of abstractness as actions in the inferior parietal lobule. These results suggest compulsory access to abstract action information in the inferior parietal lobe even when simply identifying objects.
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Affiliation(s)
- Quanjing Chen
- Department of Brain & Cognitive Sciences, University of Rochester, Rochester, NY 14627-0268, USA
| | - Frank E Garcea
- Department of Brain & Cognitive Sciences, University of Rochester, Rochester, NY 14627-0268, USA
- Center for Visual Science, University of Rochester, Rochester, NY 14627-0268, USA
| | - Robert A Jacobs
- Department of Brain & Cognitive Sciences, University of Rochester, Rochester, NY 14627-0268, USA
- Center for Visual Science, University of Rochester, Rochester, NY 14627-0268, USA
| | - Bradford Z Mahon
- Department of Brain & Cognitive Sciences, University of Rochester, Rochester, NY 14627-0268, USA
- Center for Visual Science, University of Rochester, Rochester, NY 14627-0268, USA
- Department of Neurosurgery, University of Rochester Medical Center, Rochester, NY 14627-0268, USA
- Department of Neurology, University of Rochester Medical Center, Rochester, NY 14627-0268, USA
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25
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Trotter CE, Pizzey FK, Batterson PM, Jacobs RA, Pearson J. Modest Reductions in Skin Temperature After the Onset of a Simulated Hemorrhagic Challenge Improve LBNP Tolerance Following Exercise Heat Stress. FASEB J 2018. [DOI: 10.1096/fasebj.2018.32.1_supplement.910.4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | - Faith K. Pizzey
- BiologyUniversity of Colorado Colorado SpringsColorado SpringsCO
| | | | - Robert A. Jacobs
- BiologyUniversity of Colorado Colorado SpringsColorado SpringsCO
| | - James Pearson
- BiologyUniversity of Colorado Colorado SpringsColorado SpringsCO
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26
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Deavenport-Saman A, Britt A, Smith K, Jacobs RA. Milestones and controversies in maternal and child health: examining a brief history of micronutrient fortification in the US. J Perinatol 2017; 37:1180-1184. [PMID: 28749486 DOI: 10.1038/jp.2017.121] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/30/2016] [Revised: 05/26/2017] [Accepted: 06/26/2017] [Indexed: 12/11/2022]
Abstract
Fortification of our food and drinking supply has decreased morbidity rates related to micronutrient deficiencies among mothers and their children, particularly during the perinatal and neonatal periods of development. The purpose of this historical review is to examine the impact of public policy changes related to micronutrient fortification. We provide a historical investigation of achievements and controversies related to iodine, vitamin D, fluoride and folic acid fortifications in our food and drinking supply. We also discuss the current status of fortification recommendations and their significance to maternal and child health.
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Affiliation(s)
- A Deavenport-Saman
- Department of Pediatrics, Children's Hospital Los Angeles, Los Angeles, CA, USA.,USC Center for Excellence in Developmental Disabilities, Los Angeles, CA, USA.,USC Keck School of Medicine, Los Angeles, CA, USA
| | - A Britt
- Department of Pediatrics, Children's Hospital Los Angeles, Los Angeles, CA, USA.,USC Keck School of Medicine, Los Angeles, CA, USA
| | - K Smith
- Department of Pediatrics, Children's Hospital Los Angeles, Los Angeles, CA, USA.,USC Center for Excellence in Developmental Disabilities, Los Angeles, CA, USA.,USC Keck School of Medicine, Los Angeles, CA, USA
| | - R A Jacobs
- Department of Pediatrics, Children's Hospital Los Angeles, Los Angeles, CA, USA.,USC Keck School of Medicine, Los Angeles, CA, USA
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27
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Abstract
Despite decades of research, little is known about how people visually perceive object shape. We hypothesize that a promising approach to shape perception is provided by a "visual perception as Bayesian inference" framework which augments an emphasis on visual representation with an emphasis on the idea that shape perception is a form of statistical inference. Our hypothesis claims that shape perception of unfamiliar objects can be characterized as statistical inference of 3D shape in an object-centered coordinate system. We describe a computational model based on our theoretical framework, and provide evidence for the model along two lines. First, we show that, counterintuitively, the model accounts for viewpoint-dependency of object recognition, traditionally regarded as evidence against people's use of 3D object-centered shape representations. Second, we report the results of an experiment using a shape similarity task, and present an extensive evaluation of existing models' abilities to account for the experimental data. We find that our shape inference model captures subjects' behaviors better than competing models. Taken as a whole, our experimental and computational results illustrate the promise of our approach and suggest that people's shape representations of unfamiliar objects are probabilistic, 3D, and object-centered. (PsycINFO Database Record
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Affiliation(s)
- Goker Erdogan
- Department of Brain and Cognitive Sciences, University of Rochester
| | - Robert A Jacobs
- Department of Brain and Cognitive Sciences, University of Rochester
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28
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Overlan MC, Jacobs RA, Piantadosi ST. Learning abstract visual concepts via probabilistic program induction in a Language of Thought. Cognition 2017; 168:320-334. [PMID: 28772189 DOI: 10.1016/j.cognition.2017.07.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2017] [Revised: 07/06/2017] [Accepted: 07/09/2017] [Indexed: 11/16/2022]
Abstract
The ability to learn abstract concepts is a powerful component of human cognition. It has been argued that variable binding is the key element enabling this ability, but the computational aspects of variable binding remain poorly understood. Here, we address this shortcoming by formalizing the Hierarchical Language of Thought (HLOT) model of rule learning. Given a set of data items, the model uses Bayesian inference to infer a probability distribution over stochastic programs that implement variable binding. Because the model makes use of symbolic variables as well as Bayesian inference and programs with stochastic primitives, it combines many of the advantages of both symbolic and statistical approaches to cognitive modeling. To evaluate the model, we conducted an experiment in which human subjects viewed training items and then judged which test items belong to the same concept as the training items. We found that the HLOT model provides a close match to human generalization patterns, significantly outperforming two variants of the Generalized Context Model, one variant based on string similarity and the other based on visual similarity using features from a deep convolutional neural network. Additional results suggest that variable binding happens automatically, implying that binding operations do not add complexity to peoples' hypothesized rules. Overall, this work demonstrates that a cognitive model combining symbolic variables with Bayesian inference and stochastic program primitives provides a new perspective for understanding people's patterns of generalization.
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Affiliation(s)
- Matthew C Overlan
- Department of Brain & Cognitive Sciences, University of Rochester, Rochester, NY 14627, United States.
| | - Robert A Jacobs
- Department of Brain & Cognitive Sciences, University of Rochester, Rochester, NY 14627, United States.
| | - Steven T Piantadosi
- Department of Brain & Cognitive Sciences, University of Rochester, Rochester, NY 14627, United States.
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29
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Williams ME, Wheeler BY, Linder L, Jacobs RA. Evolving Definitions of Autism and Impact on Eligibility for Developmental Disability Services: California Case Example. Intellect Dev Disabil 2017; 55:192-209. [PMID: 28608770 DOI: 10.1352/1934-9556-55.3.192] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
When establishing eligibility for developmental disability (DD) services, definitions of specific diagnostic conditions, such as autism, impact policy. Under the Medicaid home and community-based waiver program, states have discretion in determining specific program or service eligibility criteria, the nature of supports to be provided, and the number of individuals to be served. Individuals with DD, their families, and advocates have pushed to expand eligibility and improve the quality of services and supports received. This article uses a California legal case to explore the impact on individuals seeking eligibility for DD services when states rely on evolving diagnostic criteria for autism spectrum disorder. Recommendations are made for a more equitable and consistent approach to disability eligibility determination.
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Affiliation(s)
- Marian E Williams
- Marian E. Williams, Barbara Y. Wheeler, Lisa Linder, and Robert A. Jacobs, Children's Hospital Los Angeles, USC University Center for Excellence in Developmental Disabilities. Lisa Linder is now at Department of Family and Child Development, San Diego State University
| | - Barbara Y Wheeler
- Marian E. Williams, Barbara Y. Wheeler, Lisa Linder, and Robert A. Jacobs, Children's Hospital Los Angeles, USC University Center for Excellence in Developmental Disabilities. Lisa Linder is now at Department of Family and Child Development, San Diego State University
| | - Lisa Linder
- Marian E. Williams, Barbara Y. Wheeler, Lisa Linder, and Robert A. Jacobs, Children's Hospital Los Angeles, USC University Center for Excellence in Developmental Disabilities. Lisa Linder is now at Department of Family and Child Development, San Diego State University
| | - Robert A Jacobs
- Marian E. Williams, Barbara Y. Wheeler, Lisa Linder, and Robert A. Jacobs, Children's Hospital Los Angeles, USC University Center for Excellence in Developmental Disabilities. Lisa Linder is now at Department of Family and Child Development, San Diego State University
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30
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Betz CL, Smith KA, Van Speybroeck A, Hernandez FV, Jacobs RA. Movin' On Up: An Innovative Nurse-Led Interdisciplinary Health Care Transition Program. J Pediatr Health Care 2016; 30:323-38. [PMID: 26483330 DOI: 10.1016/j.pedhc.2015.08.005] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Revised: 08/26/2015] [Accepted: 08/31/2015] [Indexed: 10/22/2022]
Abstract
This article provides an overview of an innovative nurse-led interdisciplinary health care transition (HCT) model of care entitled Movin' On Up for adolescents and emerging adults (AEAs) with spina bifida (SB) that was originally implemented in 2011. The components of the HCT service model include an HCT nursing specialist, who is an advanced practice nurse; interdisciplinary health care transition plans based on the individualized needs of AEAs; an interdisciplinary HCT team that meets on a weekly basis; direct HCT services provided in the weekly SB clinic; and telephonic follow-up with AEAs, families, and providers. The characteristics of this nurse-led HCT program can be described as an integrated, interdisciplinary, and comprehensive model of care based on a life span approach. To date, a total of 210 AEAs with SB, ages 10 to 20 years, have been enrolled into the program. An important feature of this HCT service model is that it is self-supporting; it generates the revenue needed for sustainability and, unlike other HCT programs, is not reliant on extramural programmatic support. Other accomplishments of Movin' On Up include the development of a transfer protocol wherein 35 AEAs with SB have been supported in their transfer to adult care; implementation of a standardized process to ensure that service referrals to community-based services for postsecondary education, employment, training, and initiation of conservatorships are made; timely performance of evaluations; close tracking of needs and outcomes of self-management knowledge and skills instruction; and attention to equipment needs prior to transfer.
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Erdogan G, Chen Q, Garcea FE, Mahon BZ, Jacobs RA. Multisensory Part-based Representations of Objects in Human Lateral Occipital Cortex. J Cogn Neurosci 2016; 28:869-81. [PMID: 26918587 DOI: 10.1162/jocn_a_00937] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
The format of high-level object representations in temporal-occipital cortex is a fundamental and as yet unresolved issue. Here we use fMRI to show that human lateral occipital cortex (LOC) encodes novel 3-D objects in a multisensory and part-based format. We show that visual and haptic exploration of objects leads to similar patterns of neural activity in human LOC and that the shared variance between visually and haptically induced patterns of BOLD contrast in LOC reflects the part structure of the objects. We also show that linear classifiers trained on neural data from LOC on a subset of the objects successfully predict a novel object based on its component part structure. These data demonstrate a multisensory code for object representations in LOC that specifies the part structure of objects.
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Abstract
We argue for the advantages of the probabilistic language of thought (pLOT), a recently emerging approach to modeling human cognition. Work using this framework demonstrates how the pLOT (a) refines the debate between symbols and statistics in cognitive modeling, (b) permits theories that draw on insights from both nativist and empiricist approaches, (c) explains the origins of novel and complex computational concepts, and (d) provides a framework for abstraction that can link sensation and conception. In each of these areas, the pLOT provides a productive middle ground between historical divides in cognitive psychology, pointing to a promising way forward for the field.
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Affiliation(s)
| | - Robert A. Jacobs
- Department of Brain and Cognitive Sciences, University of
Rochester
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Christensen PM, Jacobs RA, Bonne T, Flück D, Bangsbo J, Lundby C. A short period of high-intensity interval training improves skeletal muscle mitochondrial function and pulmonary oxygen uptake kinetics. J Appl Physiol (1985) 2016; 120:1319-27. [PMID: 26846547 DOI: 10.1152/japplphysiol.00115.2015] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2015] [Accepted: 02/02/2016] [Indexed: 11/22/2022] Open
Abstract
The aim of the present study was to examine whether improvements in pulmonary oxygen uptake (V̇o2) kinetics following a short period of high-intensity training (HIT) would be associated with improved skeletal muscle mitochondrial function. Ten untrained male volunteers (age 26 ± 2 yr; mean ± SD) performed six HIT sessions (8-12 × 60 s at incremental test peak power; 271 ± 52 W) over a 2-wk period. Before and after the HIT period, V̇o2 kinetics was modeled during moderate-intensity cycling (110 ± 19 W). Mitochondrial function was assessed with high-resolution respirometry (HRR), and maximal activities of oxidative enzymes citrate synthase (CS) and cytochrome c oxidase (COX) were accordingly determined. In response to HIT, V̇o2 kinetics became faster (τ: 20.4 ± 4.4 vs. 28.9 ± 6.1 s; P < 0.01) and fatty acid oxidation (ETFP) and leak respiration (LN) both became elevated (P < 0.05). Activity of CS and COX did not increase in response to training. Both before and after the HIT period, fast V̇o2 kinetics (low τ values) was associated with large values for ETFP, electron transport system capacity (ETS), and electron flow specific to complex II (CIIP) (P < 0.05). Collectively, these findings support that selected measures of mitochondrial function obtained with HRR are important for fast V̇o2 kinetics and better markers than maximal oxidative enzyme activity in describing the speed of the V̇o2 response during moderate-intensity exercise.
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Affiliation(s)
- Peter M Christensen
- Department of Nutrition, Exercise and Sports, Section of Integrated Physiology, University of Copenhagen, Copenhagen, Denmark; Team Danmark (Danish Elite Sport Organization), Copenhagen, Denmark
| | - Robert A Jacobs
- Health and Physical Education, School of Teaching and Learning, Western Carolina University, Cullowhee, North Carolina; Department of Physical Therapy, Western Carolina University, Cullowhee, North Carolina; and
| | - Thomas Bonne
- Department of Nutrition, Exercise and Sports, Section of Integrated Physiology, University of Copenhagen, Copenhagen, Denmark
| | - Daniela Flück
- Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich, Zurich, Switzerland
| | - Jens Bangsbo
- Department of Nutrition, Exercise and Sports, Section of Integrated Physiology, University of Copenhagen, Copenhagen, Denmark
| | - Carsten Lundby
- Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich, Zurich, Switzerland
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Schönenberger D, Harlander S, Rajski M, Jacobs RA, Lundby AK, Adlesic M, Hejhal T, Wild PJ, Lundby C, Frew IJ. Formation of Renal Cysts and Tumors in Vhl/Trp53-Deficient Mice Requires HIF1α and HIF2α. Cancer Res 2016; 76:2025-36. [PMID: 26759234 DOI: 10.1158/0008-5472.can-15-1859] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2015] [Accepted: 01/07/2016] [Indexed: 11/16/2022]
Abstract
The von Hippel-Lindau (VHL) tumor suppressor gene is inactivated in the majority of clear cell renal cell carcinomas (ccRCC), but genetic ablation of Vhl alone in mouse models is insufficient to recapitulate human tumorigenesis. One function of pVHL is to regulate the stability of the hypoxia-inducible factors (HIF), which become constitutively activated in the absence of pVHL. In established ccRCC, HIF1α has been implicated as a renal tumor suppressor, whereas HIF2α is considered an oncoprotein. In this study, we investigated the contributions of HIF1α and HIF2α to ccRCC initiation in the context of Vhl deficiency. We found that deleting Vhl plus Hif1a or Hif2a specifically in the renal epithelium did not induce tumor formation. However, HIF1α and HIF2α differentially regulated cell proliferation, mitochondrial abundance and oxidative capacity, glycogen accumulation, and acquisition of a clear cell phenotype in Vhl-deficient renal epithelial cells. HIF1α, but not HIF2α, induced Warburg-like metabolism characterized by increased glycolysis, decreased oxygen consumption, and decreased ATP production in mouse embryonic fibroblasts, providing insights into the cellular changes potentially occurring in Vhl mutant renal cells before ccRCC formation. Importantly, deletion of either Hif1a or Hif2a completely prevented the formation of renal cysts and tumors in Vhl/Trp53 mutant mice. These findings argue that both HIF1α and HIF2α exert protumorigenic functions during the earliest stages of cyst and tumor formation in the kidney. Cancer Res; 76(7); 2025-36. ©2016 AACR.
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Affiliation(s)
| | - Sabine Harlander
- Institute of Physiology, University of Zurich, Zurich, Switzerland. Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland
| | - Michal Rajski
- Institute of Physiology, University of Zurich, Zurich, Switzerland
| | - Robert A Jacobs
- Institute of Physiology, University of Zurich, Zurich, Switzerland. Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland. Health and Physical Education, School of Teaching and Learning, Western Carolina University, Cullowhee, North Carolina
| | - Anne-Kristine Lundby
- Institute of Physiology, University of Zurich, Zurich, Switzerland. Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland
| | - Mojca Adlesic
- Institute of Physiology, University of Zurich, Zurich, Switzerland
| | - Tomas Hejhal
- Institute of Physiology, University of Zurich, Zurich, Switzerland
| | - Peter J Wild
- Institute of Surgical Pathology, University Hospital Zurich, Zurich, Switzerland
| | - Carsten Lundby
- Institute of Physiology, University of Zurich, Zurich, Switzerland. Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland
| | - Ian J Frew
- Institute of Physiology, University of Zurich, Zurich, Switzerland. Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland.
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Abstract
Mitochondrial volume density (Mito(VD)) is composed of two distinct mitochondrial subpopulations--intermyofibrillar mitochondria (Mito(IMF)) and subsarcolemmal mitochondria (Mito(SS)). With exercise training, Mito(VD) may increase by up to 40% and is, for the most part, related to an increase in Mito(IMF). Exercise-induced adaptations in mitochondrial function depend on the intensity of training and appear to be explained predominately by an increased expression of mitochondrial enzymes that facilitate aerobic metabolism. Although mitochondrial content often increases with training, it seems that mitochondrial adaptations are not needed to facilitate maximal oxygen uptake, whereas such adaptations are of greater importance for endurance capacity.
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Affiliation(s)
- Carsten Lundby
- Zürich Center for Integrative Human Physiology, Institute of Physiology, University of Zürich, Zürich, Switzerland
| | - Robert A Jacobs
- Zürich Center for Integrative Human Physiology, Institute of Physiology, University of Zürich, Zürich, Switzerland.,Health and Physical Education, School of Teaching and Learning, Western Carolina University, Cullowhee, NC, USA.,Physical Therapy Department, Western Carolina University, Cullowhee, NC, USA
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Erdogan G, Yildirim I, Jacobs RA. From Sensory Signals to Modality-Independent Conceptual Representations: A Probabilistic Language of Thought Approach. PLoS Comput Biol 2015; 11:e1004610. [PMID: 26554704 PMCID: PMC4640543 DOI: 10.1371/journal.pcbi.1004610] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2015] [Accepted: 10/17/2015] [Indexed: 12/02/2022] Open
Abstract
People learn modality-independent, conceptual representations from modality-specific sensory signals. Here, we hypothesize that any system that accomplishes this feat will include three components: a representational language for characterizing modality-independent representations, a set of sensory-specific forward models for mapping from modality-independent representations to sensory signals, and an inference algorithm for inverting forward models-that is, an algorithm for using sensory signals to infer modality-independent representations. To evaluate this hypothesis, we instantiate it in the form of a computational model that learns object shape representations from visual and/or haptic signals. The model uses a probabilistic grammar to characterize modality-independent representations of object shape, uses a computer graphics toolkit and a human hand simulator to map from object representations to visual and haptic features, respectively, and uses a Bayesian inference algorithm to infer modality-independent object representations from visual and/or haptic signals. Simulation results show that the model infers identical object representations when an object is viewed, grasped, or both. That is, the model's percepts are modality invariant. We also report the results of an experiment in which different subjects rated the similarity of pairs of objects in different sensory conditions, and show that the model provides a very accurate account of subjects' ratings. Conceptually, this research significantly contributes to our understanding of modality invariance, an important type of perceptual constancy, by demonstrating how modality-independent representations can be acquired and used. Methodologically, it provides an important contribution to cognitive modeling, particularly an emerging probabilistic language-of-thought approach, by showing how symbolic and statistical approaches can be combined in order to understand aspects of human perception.
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Affiliation(s)
- Goker Erdogan
- Department of Brain & Cognitive Sciences, University of Rochester, Rochester, New York, United States of America
| | - Ilker Yildirim
- Department of Brain & Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States of America
- Laboratory of Neural Systems, The Rockefeller University, New York, New York, United States of America
| | - Robert A. Jacobs
- Department of Brain & Cognitive Sciences, University of Rochester, Rochester, New York, United States of America
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Jacobs RA, Lundby AKM, Fenk S, Gehrig S, Siebenmann C, Flück D, Kirk N, Hilty MP, Lundby C. Twenty-eight days of exposure to 3454 m increases mitochondrial volume density in human skeletal muscle. J Physiol 2015; 594:1151-66. [PMID: 26339730 DOI: 10.1113/jp271118] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Accepted: 08/28/2015] [Indexed: 12/11/2022] Open
Abstract
The role of hypoxia on skeletal muscle mitochondria is controversial. Studies superimposing exercise training on hypoxic exposure demonstrate an increase in skeletal muscle mitochondrial volume density (Mito(VD)) over equivalent normoxic training. In contrast, reductions in both skeletal muscle mass and Mito(VD) have been reported following mountaineering expeditions. These observations may, however, be confounded by negative energy balance, which may obscure the results. Accordingly we sought to examine the effects of high altitude hypoxic exposure on mitochondrial characteristics, with emphasis on Mito(VD), while minimizing changes in energy balance. For this purpose, skeletal muscle biopsies were obtained from nine lowlanders at sea level (Pre) and following 7 and 28 days of exposure to 3454 m. Maximal ergometer power output, whole body weight and composition, leg lean mass and skeletal muscle fibre area all remained unchanged following the altitude exposure. Transmission electron microscopy determined that intermyofibrillar (IMF) Mito(VD) was augmented (P = 0.028) by 11.5 ± 9.2% from Pre (5.05 ± 0.9%) to 28 Days (5.61 ± 0.04%). In contrast, there was no change in subsarcolemmal (SS) Mito(VD). As a result, total Mito(VD) (IMF + SS) was increased (P = 0.031) from 6.20 ± 1.5% at Pre to 6.62 ± 1.4% at 28 Days (7.8 ± 9.3%). At the same time no changes in mass-specific respiratory capacities, mitochondrial protein or antioxidant content were found. This study demonstrates that skeletal muscle Mito(VD) may increase with 28 days acclimation to 3454 m.
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Affiliation(s)
- Robert A Jacobs
- Zürich Centre for Integrative Human Physiology, Institute of Physiology, University of Zürich, Switzerland.,Health and Physical Education, School of Teaching and Learning, Western Carolina University, Cullowhee, NC, USA.,Physical Therapy Department, Western Carolina University, Cullowhee, NC, USA
| | | | - Simone Fenk
- Zürich Centre for Integrative Human Physiology, Institute of Physiology, University of Zürich, Switzerland
| | - Saskia Gehrig
- Zürich Centre for Integrative Human Physiology, Institute of Physiology, University of Zürich, Switzerland
| | - Christoph Siebenmann
- Zürich Centre for Integrative Human Physiology, Institute of Physiology, University of Zürich, Switzerland.,Department of Environmental Physiology, School of Technology and Health, Royal Institute of Technology, Solna, Sweden
| | - Daniela Flück
- Zürich Centre for Integrative Human Physiology, Institute of Physiology, University of Zürich, Switzerland
| | - Niels Kirk
- Zürich Centre for Integrative Human Physiology, Institute of Physiology, University of Zürich, Switzerland
| | | | - Carsten Lundby
- Zürich Centre for Integrative Human Physiology, Institute of Physiology, University of Zürich, Switzerland
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Montero D, Cathomen A, Jacobs RA, Flück D, de Leur J, Keiser S, Bonne T, Kirk N, Lundby AK, Lundby C. Haematological rather than skeletal muscle adaptations contribute to the increase in peak oxygen uptake induced by moderate endurance training. J Physiol 2015; 593:4677-88. [PMID: 26282186 DOI: 10.1113/jp270250] [Citation(s) in RCA: 119] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2015] [Accepted: 08/04/2015] [Indexed: 12/26/2022] Open
Abstract
It remains unclear whether improvements in peak oxygen uptake (V̇(O2peak)) following endurance training (ET) are primarily determined by central and/or peripheral adaptations. Herein, we tested the hypothesis that the improvement in V̇(O2peak) following 6 weeks of ET is mainly determined by haematological rather than skeletal muscle adaptations. Sixteen untrained healthy male volunteers (age = 25 ± 4 years, V̇(O2peak) = 3.5 ± 0.5 l min(-1)) underwent supervised ET (6 weeks, 3-4 sessions per week). V̇(O2peak), peak cardiac output (Q̇(peak)), haemoglobin mass (Hb(mass)) and blood volumes were assessed prior to and following ET. Skeletal muscle biopsies were analysed for mitochondrial volume density (Mito(VD)), capillarity, fibre types and respiratory capacity (OXPHOS). After the post-ET assessment, red blood cell volume (RBCV) was re-established at the pre-ET level by phlebotomy and V̇(O2peak) and Q̇(peak) were measured again. We speculated that the contribution of skeletal muscle adaptations to the ET-induced increase in V̇(O2peak) would be revealed when controlling for haematological adaptations. V̇(O2peak) and Q̇(peak) were increased (P < 0.05) following ET (9 ± 8 and 7 ± 6%, respectively) and decreased (P < 0.05) after phlebotomy (-7 ± 7 and -10 ± 7%). RBCV, plasma volume and Hb(mass) all increased (P < 0.05) after ET (8 ± 4, 4 ± 6 and 6 ± 5%). As for skeletal muscle adaptations, capillary-to-fibre ratio and total Mito(VD) increased (P < 0.05) following ET (18 ± 16 and 43 ± 30%), but OXPHOS remained unaltered. Through stepwise multiple regression analysis, Q̇(peak), RBCV and Hb(mass) were found to be independent predictors of V̇(O2peak). In conclusion, the improvement in V̇(O2peak) following 6 weeks of ET is primarily attributed to increases in Q̇(peak) and oxygen-carrying capacity of blood in untrained healthy young subjects.
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Affiliation(s)
- David Montero
- Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland
| | - Adrian Cathomen
- Institute of Human Movement Sciences and Sport, ETH Zurich, Switzerland
| | - Robert A Jacobs
- Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland.,Health and Physical Education, School of Teaching and Learning, Western Carolina University, Cullowhee, NC, USA
| | - Daniela Flück
- Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland
| | - Jeroen de Leur
- Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland
| | - Stefanie Keiser
- Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland
| | - Thomas Bonne
- Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland
| | - Niels Kirk
- Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland
| | - Anne-Kristine Lundby
- Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland
| | - Carsten Lundby
- Zurich Centre for Integrative Human Physiology (ZIHP), University of Zurich, Institute of Physiology, Switzerland
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Robach P, Bonne T, Flück D, Bürgi S, Toigo M, Jacobs RA, Lundby C. Hypoxic training: effect on mitochondrial function and aerobic performance in hypoxia. Med Sci Sports Exerc 2015; 46:1936-45. [PMID: 24674976 DOI: 10.1249/mss.0000000000000321] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
PURPOSE The effects of hypoxic training on exercise performance remain controversial. Here, we tested the hypotheses that i) hypoxic training possesses ergogenic effects at sea level and altitude and ii) the benefits are primarily mediated by improved mitochondrial function of the skeletal muscle. METHODS We determined aerobic performance (incremental test to exhaustion and time trial for a set amount of work) in moderately trained subjects undergoing 6 wk of endurance training (3-4 times per week, 60 min per session) in normoxia (placebo, n = 8) or normobaric hypoxia (FIO2 = 0.15, n = 9) using a double-blind and randomized design. Exercise tests were performed in normoxia and acute hypoxia (FIO2 = 0.15). Skeletal muscle mitochondrial respiratory capacities and electron coupling efficiencies were measured via high-resolution respirometry. Total hemoglobin mass was assessed by carbon monoxide rebreathing. RESULTS Skeletal muscle respiratory capacity was not altered by training or hypoxia; however, electron coupling control respective to fat oxidation slightly diminished with hypoxic training. Hypoxic training did increase total hemoglobin mass more than the placebo (8.4% vs 3.3%, P = 0.02). In normoxia, hypoxic training had no additive effect on maximal measures of oxygen uptake or time trial performance. In acute hypoxia, hypoxic training conferred no advantage on maximal oxygen uptake but tended to enhance time trial performance more than normoxic training (52% vs 32%, P = 0.09). CONCLUSIONS Our data suggest that, in moderately trained subjects, 6 wk of hypoxic training possesses no ergogenic effect at sea level. It is not excluded that hypoxic training might facilitate endurance capacity at moderate altitude; however, this issue is still open and needs to be further examined.
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Affiliation(s)
- Paul Robach
- 1Ecole Nationale des Sports de Montagne, site de l'Ecole Nationale de Ski et d'Alpinisme, Chamonix, FRANCE; 2Department of Exercise and Sport Sciences, University of Copenhagen, Copenhagen, DENMARK; 3Zürich Center for Integrative Human Physiology, University of Zürich, Zürich, SWITZERLAND; 4Institute of Physiology, University of Zürich, Zürich, SWITZERLAND; and 5Exercise Physiology, Institute of Human Movement Sciences, Eidgenössische Technische Hochschule Zürich, Zürich, SWITZERLAND
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Jacobs RA. Con: Live high-train low does not improve sea-level performance beyond that achieved with the equivalent living and training at sea level. High Alt Med Biol 2014; 14:328-30. [PMID: 24377336 DOI: 10.1089/ham.2013.1040] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Robert A Jacobs
- 1 Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich , Zurich, Switzerland
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Abstract
A growing body of scientific evidence suggests that visual working memory and statistical learning are intrinsically linked. Although visual working memory is severely resource limited, in many cases, it makes efficient use of its available resources by adapting to statistical regularities in the visual environment. However, experimental evidence also suggests that there are clear limits and biases in statistical learning. This raises the intriguing possibility that performance limitations observed in visual working memory tasks can to some degree be explained in terms of limits and biases in statistical-learning ability, rather than limits in memory capacity.
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Affiliation(s)
| | | | - Robert A. Jacobs
- Department of Brain and Cognitive Sciences, University of Rochester
| | - David C. Knill
- Department of Brain and Cognitive Sciences, University of Rochester
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Bonne TC, Doucende G, Flück D, Jacobs RA, Nordsborg NB, Robach P, Walther G, Lundby C. Phlebotomy eliminates the maximal cardiac output response to six weeks of exercise training. Am J Physiol Regul Integr Comp Physiol 2014; 306:R752-60. [DOI: 10.1152/ajpregu.00028.2014] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
With this study we tested the hypothesis that 6 wk of endurance training increases maximal cardiac output (Q̇max) relatively more by elevating blood volume (BV) than by inducing structural and functional changes within the heart. Nine healthy but untrained volunteers (V̇o2max 47 ± 5 ml·min−1·kg−1) underwent supervised training (60 min; 4 times weekly at 65% V̇o2max for 6 wk), and Q̇max was determined by inert gas rebreathing during cycle ergometer exercise before and after the training period. After the training period, blood volume (determined in duplicates by CO rebreathing) was reestablished to pretraining values by phlebotomy and Q̇max was quantified again. Resting echography revealed no structural heart adaptations as a consequence of the training intervention. After the training period, plasma volume (PV), red blood cell volume (RBCV), and BV increased ( P < 0.05) by 147 ± 168 (5 ± 5%), 235 ± 64 (10 ± 3%), and 382 ± 204 ml (7 ± 4%), respectively. V̇o2max was augmented ( P < 0.05) by 10 ± 7% after the training period and decreased ( P < 0.05) by 8 ± 7% with phlebotomy. Concomitantly, Q̇max was increased ( P < 0.05) from 18.9 ± 2.1 to 20.4 ± 2.3 l/min (9 ± 6%) as a consequence of the training intervention, and after normalization of BV by phlebotomy Q̇max returned to pretraining values (18.1 ± 2.5 l/min; 12 ± 5% reversal). Thus the exercise training-induced increase in BV is the main mechanism increasing Q̇max after 6 wk of endurance training in previously untrained subjects.
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Affiliation(s)
- Thomas C. Bonne
- Department of Exercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Gregory Doucende
- Laboratoire Performance et Santé en Altitude, Université de Perpignan, Font-Romeu, France
| | - Daniela Flück
- Zürich Center for Integrative Human Physiology (ZIHP), University of Zürich, Zürich, Switzerland
| | - Robert A. Jacobs
- Zürich Center for Integrative Human Physiology (ZIHP), University of Zürich, Zürich, Switzerland
| | - Nikolai B. Nordsborg
- Department of Exercise and Sport Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Paul Robach
- Ecole Nationale des Sports de Montagne, site de l'Ecole Nationale de Ski et d'Alpinisme, Chamonix, France
| | - Guillaume Walther
- Laboratoire de Pharm-Ecologie Cardiovasculaire, Université d'Avignon, Avignon, France
| | - Carsten Lundby
- Zürich Center for Integrative Human Physiology (ZIHP), University of Zürich, Zürich, Switzerland
- Food & Nutrition & Sport Science, Gothenburg University, Sweden
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Jacobs RA. Rebuttal to the pro statement. High Alt Med Biol 2014; 14:333. [PMID: 24377338 DOI: 10.1089/ham.2013.1076] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
- Robert A Jacobs
- 1 Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich , Zurich, Switzerland
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Abstract
Lactate is an important intermediate metabolite in human bioenergetics and is oxidized in many different tissues including the heart, brain, kidney, adipose tissue, liver, and skeletal muscle. The mechanism(s) explaining the metabolism of lactate in these tissues, however, remains unclear. Here, we analyze the ability of skeletal muscle to respire lactate by using an in situ mitochondrial preparation that leaves the native tubular reticulum and subcellular interactions of the organelle unaltered. Skeletal muscle biopsies were obtained from vastus lateralis muscle in 16 human subjects. Samples were chemically permeabilized with saponin, which selectively perforates the sarcolemma and facilitates the loss of cytosolic content without altering mitochondrial membranes, structure, and subcellular interactions. High-resolution respirometry was performed on permeabilized muscle biopsy preparations. By use of four separate and specific substrate titration protocols, the respirometric analysis revealed that mitochondria were capable of oxidizing lactate in the absence of exogenous LDH. The titration of lactate and NAD(+) into the respiration medium stimulated respiration (P ≤ 0.003). The addition of exogenous LDH failed to increase lactate-stimulated respiration (P = 1.0). The results further demonstrate that human skeletal muscle mitochondria cannot directly oxidize lactate within the mitochondrial matrix. Alternately, these data support previous claims that lactate is converted to pyruvate within the mitochondrial intermembrane space with the pyruvate subsequently taken into the mitochondrial matrix where it enters the TCA cycle and is ultimately oxidized.
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Affiliation(s)
- Robert A Jacobs
- Zurich Center for Integrative Human Physiology, Zurich, Switzerland.
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45
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Abstract
Experimental evidence suggests that the content of a memory for even a simple display encoded in visual short-term memory (VSTM) can be very complex. VSTM uses organizational processes that make the representation of an item dependent on the feature values of all displayed items as well as on these items' representations. Here, we develop a probabilistic clustering theory (PCT) for modeling the organization of VSTM for simple displays. PCT states that VSTM represents a set of items in terms of a probability distribution over all possible clusterings or partitions of those items. Because PCT considers multiple possible partitions, it can represent an item at multiple granularities or scales simultaneously. Moreover, using standard probabilistic inference, it automatically determines the appropriate partitions for the particular set of items at hand and the probabilities or weights that should be allocated to each partition. A consequence of these properties is that PCT accounts for experimental data that have previously motivated hierarchical models of VSTM, thereby providing an appealing alternative to hierarchical models with prespecified, fixed structures. We explore both an exact implementation of PCT based on Dirichlet process mixture models and approximate implementations based on Bayesian finite mixture models. We show that a previously proposed 2-level hierarchical model can be seen as a special case of PCT with a single cluster. We show how a wide range of previously reported results on the organization of VSTM can be understood in terms of PCT. In particular, we find that, consistent with empirical evidence, PCT predicts biases in estimates of the feature values of individual items and also predicts a novel form of dependence between estimates of the feature values of different items. We qualitatively confirm this last prediction in 3 novel experiments designed to directly measure biases and dependencies in subjects' estimates.
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Affiliation(s)
- A Emin Orhan
- Department of Brain & Cognitive Sciences, University of Rochester, NY 14627, USA.
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46
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Sims CR, Neth H, Jacobs RA, Gray WD. Melioration as rational choice: Sequential decision making in uncertain environments. Psychol Rev 2013; 120:139-54. [DOI: 10.1037/a0030850] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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47
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Abstract
Natural outdoor conditions pose unique obstacles for researchers, above and beyond those inherent to all mobile eye-tracking research. During analyses of a large set of eye-tracking data collected on geologists examining outdoor scenes, we have found that the nature of calibration, pupil identification, fixation detection, and gaze analysis all require procedures different from those typically used for indoor studies. Here, we discuss each of these challenges and present solutions, which together define a general method useful for investigations relying on outdoor eye-tracking data. We also discuss recommendations for improving the tools that are available, to further increase the accuracy and utility of outdoor eye-tracking data.
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48
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Jacobs RA, Lundby C. Mitochondria express enhanced quality as well as quantity in association with aerobic fitness across recreationally active individuals up to elite athletes. J Appl Physiol (1985) 2012; 114:344-50. [PMID: 23221957 DOI: 10.1152/japplphysiol.01081.2012] [Citation(s) in RCA: 144] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Changes in skeletal muscle respiratory capacity parallel that of aerobic fitness. It is unknown whether mitochondrial content, alone, can fully account for these differences in skeletal muscle respiratory capacity. The aim of the present study was to examine quantitative and qualitative mitochondrial characteristics across four different groups (n = 6 each), separated by cardiorespiratory fitness. High-resolution respirometry was performed on muscle samples to compare respiratory capacity and efficiency in active, well-trained, highly trained, and elite individuals. Maximal exercise capacity (ml O(2)·min(-1)·kg(-1)) differed across all groups, with mean ± SD values of 51 ± 4, 64 ± 5, 71 ± 2, and 77 ± 3, respectively. Mitochondrial content assessed by citrate synthase activity was higher in elite trained compared with active and well-trained (29 ± 7 vs. 16 ± 4 and 19 ± 4 nmol·min(-1)·mg wet wt(-1), respectively). When normalizing respiration to mitochondrial content, the respiratory capacities during maximal fatty acid oxidation (P = 0.003), maximal state 3 respiration (P = 0.021), and total electron transport system capacity (P = 0.008) improved with respect to maximal exercise capacity. The coupling efficiency of β-oxidation, however, expressed no difference across groups. These data demonstrate the quantitative and qualitative differences that exist in skeletal muscle mitochondrial respiratory capacity and efficiency across individuals that differ in aerobic capacity. Mitochondrial-specific respiration capacities during β-oxidation, maximal oxidative phosphorylation, and electron transport system capacity all correspondingly improve with aerobic capacity, independent of mitochondrial content in human skeletal muscle.
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Affiliation(s)
- Robert A Jacobs
- Zurich Center for Integrative Human Physiology, Zurich, Switzerland.
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49
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Abstract
It is debatable whether differences in mitochondrial function exist across skeletal muscle types and whether mouse skeletal muscle mitochondrial function can serve as a valid model for human skeletal muscle mitochondrial function. The aims of this study were to compare and contrast three different mouse skeletal muscles and to identify the mouse muscle that most closely resembles human skeletal muscle respiratory capacity and control. Mouse quadriceps (QUAD(M)), soleus (SOL(M)) and gastrocnemius (GAST(M)) skeletal muscles were obtained from 8- to 10-week-old healthy mice (n = 8), representing mixed, oxidative and glycolytic muscle, respectively. Skeletal muscle samples were also collected from young, active, healthy human subjects (n = 8) from the vastis lateralis (QUAD(H)). High-resolution respirometry was used to examine mitochondrial function in all skeletal muscle samples, and mitochondrial content was quantified with citrate synthase activity. Mass-specific respiration was higher across all respiratory states in SOL(M) versus both GAST(M) and QUAD(H) (P < 0.01). When controlling for mitochondrial content, however, SOL(M) respiration was lower than GAST(M) and QUAD(H) (P < 0.05 and P < 0.01, respectively). When comparing respiratory capacity between mouse and human muscle, QUAD(M) exhibited only one different respiratory state when compared with QUAD(H). These results demonstrate that qualitative differences in mitochondrial function exist between different mouse skeletal muscles types when respiratory capacity is normalized to mitochondrial content, and that skeletal muscle respiratory capacity in young, healthy QUAD(M) does correspond well with that of young, healthy QUAD(H).
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Affiliation(s)
- Robert A Jacobs
- Institute of Physiology and Zurich Center for Integrative Human Physiology, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
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50
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Abstract
Hypoxia-stimulated erythropoiesis, such as that observed when red blood cell volume (RCV) increases in response to high-altitude exposure, is well understood while the physiological importance is not. Maximal exercise tests are often performed in hypoxic conditions following some form of RCV manipulation in an attempt to elucidate oxygen transport limitations at moderate to high altitudes. Such attempts, however, have not made clear the extent to which RCV is of benefit to exercise at such elevations. Changes in RCV at sea level clearly have a direct influence on maximal exercise capacity. Nonetheless, at elevations above 3000 m, the evidence is not that clear. Certain studies demonstrate either a direct benefit or decrement to exercise capacity in response to an increase or decrease, respectively, in RCV whereas other studies report negligible effects of RCV manipulation on exercise capacity. Adding to the uncertainty regarding the importance of RCV at high altitude is the observation that Andean and Tibetan high-altitude natives exhibit similar exercise capacities at high altitude (3900 m) even though Andean natives often present with a higher percent haematocrit (Hct) when compared with both lowland natives and Tibetans. The current review summarizes past literature that has examined the effect of RCV changes on maximal exercise capacity at moderate to high altitudes, and discusses the explanation elucidating these seemingly paradoxical observations.
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Affiliation(s)
- Robert A Jacobs
- Institute of Veterinary Physiology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
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