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Abstract
This article argues that consciousness has a logically sound, explanatory framework, different from typical accounts that suffer from hidden mysticism. The article has three main parts. The first describes background principles concerning information processing in the brain, from which one can deduce a general, rational framework for explaining consciousness. The second part describes a specific theory that embodies those background principles, the Attention Schema Theory. In the past several years, a growing body of experimental evidence-behavioral evidence, brain imaging evidence, and computational modeling-has addressed aspects of the theory. The final part discusses the evolution of consciousness. By emphasizing the specific role of consciousness in cognition and behavior, the present approach leads to a proposed account of how consciousness may have evolved over millions of years, from fish to humans. The goal of this article is to present a comprehensive, overarching framework in which we can understand scientifically what consciousness is and what key adaptive roles it plays in brain function.
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Bordia T, Zahr NM. The Inferior Colliculus in Alcoholism and Beyond. Front Syst Neurosci 2020; 14:606345. [PMID: 33362482 PMCID: PMC7759542 DOI: 10.3389/fnsys.2020.606345] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Accepted: 11/02/2020] [Indexed: 12/28/2022] Open
Abstract
Post-mortem neuropathological and in vivo neuroimaging methods have demonstrated the vulnerability of the inferior colliculus to the sequelae of thiamine deficiency as occurs in Wernicke-Korsakoff Syndrome (WKS). A rich literature in animal models ranging from mice to monkeys-including our neuroimaging studies in rats-has shown involvement of the inferior colliculi in the neural response to thiamine depletion, frequently accomplished with pyrithiamine, an inhibitor of thiamine metabolism. In uncomplicated alcoholism (i.e., absent diagnosable neurological concomitants), the literature citing involvement of the inferior colliculus is scarce, has nearly all been accomplished in preclinical models, and is predominately discussed in the context of ethanol withdrawal. Our recent work using novel, voxel-based analysis of structural Magnetic Resonance Imaging (MRI) has demonstrated significant, persistent shrinkage of the inferior colliculus using acute and chronic ethanol exposure paradigms in two strains of rats. We speculate that these consistent findings should be considered from the perspective of the inferior colliculi having a relatively high CNS metabolic rate. As such, they are especially vulnerable to hypoxic injury and may be provide a common anatomical link among a variety of disparate insults. An argument will be made that the inferior colliculi have functions, possibly related to auditory gating, necessary for awareness of the external environment. Multimodal imaging including diffusion methods to provide more accurate in vivo visualization and quantification of the inferior colliculi may clarify the roles of brain stem nuclei such as the inferior colliculi in alcoholism and other neuropathologies marked by altered metabolism.
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Affiliation(s)
- Tanuja Bordia
- Neuroscience Program, SRI International, Menlo Park, CA, United States
| | - Natalie M. Zahr
- Neuroscience Program, SRI International, Menlo Park, CA, United States
- Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, CA, United States
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Gravot CM, Knorr AG, Glasauer S, Straka H. It's not all black and white: visual scene parameters influence optokinetic reflex performance in Xenopus laevis tadpoles. ACTA ACUST UNITED AC 2018; 220:4213-4224. [PMID: 29141881 DOI: 10.1242/jeb.167700] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Accepted: 09/16/2017] [Indexed: 11/20/2022]
Abstract
The maintenance of visual acuity during active and passive body motion is ensured by gaze-stabilizing reflexes that aim at minimizing retinal image slip. For the optokinetic reflex (OKR), large-field visual motion of the surround forms the essential stimulus that activates eye movements. Properties of the moving visual world influence cognitive motion perception and the estimation of visual image velocity. Therefore, the performance of brainstem-mediated visuo-motor behaviors might also depend on image scene characteristics. Employing semi-intact preparations of mid-larval stages of Xenopus laevis tadpoles, we studied the influence of contrast polarity, intensity, contour shape and different motion stimulus patterns on the performance of the OKR and multi-unit optic nerve discharge during motion of a large-field visual scene. At high contrast intensities, the OKR amplitude was significantly larger for visual scenes with a positive contrast (bright dots on a dark background) compared with those with a negative contrast. This effect persisted for luminance-matched pairs of stimuli, and was independent of contour shape. The relative biases of OKR performance along with the independence of the responses from contour shape were closely matched by the optic nerve discharge evoked by the same visual stimuli. However, the multi-unit activity of retinal ganglion cells in response to a small single moving vertical edge was strongly influenced by the light intensity in the vertical neighborhood. This suggests that the underlying mechanism of OKR biases related to contrast polarity directly derives from visual motion-processing properties of the retinal circuitry.
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Affiliation(s)
- Céline M Gravot
- Department Biology II, Ludwig-Maximilians-Universität München, Großhaderner Str. 2, 82152 Planegg, Germany .,Graduate School of Systemic Neurosciences, Ludwig-Maximilians-Universität München, Großhaderner Str. 2, 82152 Planegg, Germany
| | - Alexander G Knorr
- Center for Sensorimotor Research, Department of Neurology, University Hospital Munich, Feodor-Lynen-Str. 19, 81377 Munich, Germany.,Institute for Cognitive Systems, TUM Department of Electrical and Computer Engineering, Technical University of Munich, Karlstr. 45/II, 80333 Munich, Germany
| | - Stefan Glasauer
- Center for Sensorimotor Research, Department of Neurology, University Hospital Munich, Feodor-Lynen-Str. 19, 81377 Munich, Germany
| | - Hans Straka
- Department Biology II, Ludwig-Maximilians-Universität München, Großhaderner Str. 2, 82152 Planegg, Germany
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Svirskis G, Baranauskas G, Svirskiene N, Tkatch T. Visual Stimuli Evoked Action Potentials Trigger Rapidly Propagating Dendritic Calcium Transients in the Frog Optic Tectum Layer 6 Neurons. PLoS One 2015; 10:e0139472. [PMID: 26414356 PMCID: PMC4586134 DOI: 10.1371/journal.pone.0139472] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2015] [Accepted: 09/13/2015] [Indexed: 11/19/2022] Open
Abstract
The superior colliculus in mammals or the optic tectum in amphibians is a major visual information processing center responsible for generation of orientating responses such as saccades in monkeys or prey catching avoidance behavior in frogs. The conserved structure function of the superior colliculus the optic tectum across distant species such as frogs, birds monkeys permits to draw rather general conclusions after studying a single species. We chose the frog optic tectum because we are able to perform whole-cell voltage-clamp recordings fluorescence imaging of tectal neurons while they respond to a visual stimulus. In the optic tectum of amphibians most visual information is processed by pear-shaped neurons possessing long dendritic branches, which receive the majority of synapses originating from the retinal ganglion cells. Since the first step of the retinal input integration is performed on these dendrites, it is important to know whether this integration is enhanced by active dendritic properties. We demonstrate that rapid calcium transients coinciding with the visual stimulus evoked action potentials in the somatic recordings can be readily detected up to the fine branches of these dendrites. These transients were blocked by calcium channel blockers nifedipine CdCl2 indicating that calcium entered dendrites via voltage-activated L-type calcium channels. The high speed of calcium transient propagation, >300 μm in <10 ms, is consistent with the notion that action potentials, actively propagating along dendrites, open voltage-gated L-type calcium channels causing rapid calcium concentration transients in the dendrites. We conclude that such activation by somatic action potentials of the dendritic voltage gated calcium channels in the close vicinity to the synapses formed by axons of the retinal ganglion cells may facilitate visual information processing in the principal neurons of the frog optic tectum.
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Affiliation(s)
- Gytis Svirskis
- Neurophysiology laboratory, Neuroscience Institute, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Gytis Baranauskas
- Neurophysiology laboratory, Neuroscience Institute, Lithuanian University of Health Sciences, Kaunas, Lithuania
- * E-mail:
| | - Natasa Svirskiene
- Neurophysiology laboratory, Neuroscience Institute, Lithuanian University of Health Sciences, Kaunas, Lithuania
| | - Tatiana Tkatch
- Neurophysiology laboratory, Neuroscience Institute, Lithuanian University of Health Sciences, Kaunas, Lithuania
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Dutta A, Gutfreund Y. Saliency mapping in the optic tectum and its relationship to habituation. Front Integr Neurosci 2014; 8:1. [PMID: 24474908 PMCID: PMC3893637 DOI: 10.3389/fnint.2014.00001] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2013] [Accepted: 01/02/2014] [Indexed: 12/02/2022] Open
Abstract
Habituation of the orienting response has long served as a model system for studying fundamental psychological phenomena such as learning, attention, decisions, and surprise. In this article, we review an emerging hypothesis that the evolutionary role of the superior colliculus (SC) in mammals or its homolog in birds, the optic tectum (OT), is to select the most salient target and send this information to the appropriate brain regions to control the body and brain orienting responses. Recent studies have begun to reveal mechanisms of how saliency is computed in the OT/SC, demonstrating a striking similarity between mammals and birds. The saliency of a target can be determined by how different it is from the surrounding objects, by how different it is from its history (that is habituation) and by how relevant it is for the task at hand. Here, we will first review evidence, mostly from primates and barn owls, that all three types of saliency computations are linked in the OT/SC. We will then focus more on neural adaptation in the OT and its possible link to temporal saliency and habituation.
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Affiliation(s)
- Arkadeb Dutta
- Rappaport Family Institute for Research in the Medical Sciences, Ruth and Bruce Rappaport Faculty of Medicine, Technion - Israel Institute of Technology Haifa, Israel
| | - Yoram Gutfreund
- Rappaport Family Institute for Research in the Medical Sciences, Ruth and Bruce Rappaport Faculty of Medicine, Technion - Israel Institute of Technology Haifa, Israel
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Meier PS, Bickelmann C, Scheyer TM, Koyabu D, Sánchez-Villagra MR. Evolution of bone compactness in extant and extinct moles (Talpidae): exploring humeral microstructure in small fossorial mammals. BMC Evol Biol 2013; 13:55. [PMID: 23442022 PMCID: PMC3599842 DOI: 10.1186/1471-2148-13-55] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2012] [Accepted: 02/19/2013] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND Talpids include forms with different degree of fossoriality, with major specializations in the humerus in the case of the fully fossorial moles. We studied the humeral microanatomy of eleven extant and eight extinct talpid taxa of different lifestyles and of two non-fossorial outgroups and examined the effects of size and phylogeny. We tested the hypothesis that bone microanatomy is different in highly derived humeri of fossorial taxa than in terrestrial and semi-aquatic ones, likely due to special mechanical strains to which they are exposed to during digging. This study is the first comprehensive examination of histological parameters in an ecologically diverse and small-sized mammalian clade. RESULTS No pattern of global bone compactness was found in the humeri of talpids that could be related to biomechanical specialization, phylogeny or size. The transition zone from the medullary cavity to the cortical compacta was larger and the ellipse ratio smaller in fossorial talpids than in non-fossorial talpids. No differences were detected between the two distantly related fossorial clades, Talpini and Scalopini. CONCLUSIONS At this small size, the overall morphology of the humerus plays a predominant role in absorbing the load, and microanatomical features such as an increase in bone compactness are less important, perhaps due to insufficient gravitational effects. The ellipse ratio of bone compactness shows relatively high intraspecific variation, and therefore predictions from this ratio based on single specimens are invalid.
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Affiliation(s)
- Patricia S Meier
- Paläontologisches Institut und Museum, Universität Zürich, Karl Schmid-Strasse 4, Zürich, CH-8006, Switzerland
| | - Constanze Bickelmann
- Paläontologisches Institut und Museum, Universität Zürich, Karl Schmid-Strasse 4, Zürich, CH-8006, Switzerland
- Current address: Museum für Naturkunde-Leibniz-Institut für Evolutions-und Biodiversitätsforschung, Invalidenstrasse 43, Berlin, D-10115, Germany
| | - Torsten M Scheyer
- Paläontologisches Institut und Museum, Universität Zürich, Karl Schmid-Strasse 4, Zürich, CH-8006, Switzerland
| | - Daisuke Koyabu
- Paläontologisches Institut und Museum, Universität Zürich, Karl Schmid-Strasse 4, Zürich, CH-8006, Switzerland
| | - Marcelo R Sánchez-Villagra
- Paläontologisches Institut und Museum, Universität Zürich, Karl Schmid-Strasse 4, Zürich, CH-8006, Switzerland
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