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Dweck CS, Dixon ML, Gross JJ. What Is Motivation, Where Does It Come from, and How Does It Work? Motivation Science 2023. [DOI: 10.1093/oso/9780197662359.003.0001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Abstract
Motivation is the process that drives, selects, and directs goals and behaviors. Motivation typically arises out of the person’s needs, and it then comes to life through the person’s specific goals. In this essay, the authors examine the concept of “needs” as the crucible from which motivated behavior arises because all individuals are born with needs that jump-start the goal-oriented, motivated behaviors that are critical to survival and thriving. These are both physical needs (such as hunger and thirst) and psychological needs (such as the need for social relationships, optimal predictability, and competence). The aim of motivation is therefore to bring about a desired (need, goal) state. Motivation underlies and organizes all aspects of a person’s psychology. As it does so, motivation “glues” a person together as a functioning individual in their culture and context.
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Goldin PR, Thurston M, Allende S, Moodie C, Dixon ML, Heimberg RG, Gross JJ. Evaluation of Cognitive Behavioral Therapy vs Mindfulness Meditation in Brain Changes During Reappraisal and Acceptance Among Patients With Social Anxiety Disorder: A Randomized Clinical Trial. JAMA Psychiatry 2021; 78:1134-1142. [PMID: 34287622 PMCID: PMC8295897 DOI: 10.1001/jamapsychiatry.2021.1862] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [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] [Indexed: 11/14/2022]
Abstract
IMPORTANCE Cognitive behavioral group therapy (CBGT) and mindfulness-based stress reduction (MBSR) are thought to help patients with social anxiety disorder (SAD) via distinct emotion-regulation mechanisms. However, no study has compared the effects of CBGT and MBSR on brain and negative emotion indicators of cognitive reappraisal and acceptance in patients with SAD. OBJECTIVE To investigate the effects of CBGT and MBSR on reappraisal and acceptance in patients with SAD and to test whether treatment-associated brain changes are associated with social anxiety symptoms 1 year posttreatment. DESIGN, SETTING, AND PARTICIPANTS In this randomized clinical trial, a total of 108 unmedicated adults diagnosed with generalized SAD were randomly assigned to 12 weeks of CBGT, MBSR, or waitlist. The final sample included 31 patients receiving CBGT, 32 patients receiving MBSR, and 32 waitlist patients. Data were collected at the psychology department at Stanford University from September 2012 to December 2014. Data were analyzed from February 2019 to December 2020. INTERVENTIONS CBGT and MBSR. MAIN OUTCOMES AND MEASURES Changes in self-reported negative emotion and functional magnetic resonance imaging (fMRI) blood oxygen level-dependent (BOLD) signal within an a priori-defined brain search region mask derived from a meta-analysis of cognitive reappraisal and attention regulation 1 year posttreatment. RESULTS Of 108 participants, 60 (56%) were female. The mean (SD) age was 32.7 (8.0) years. Self-reported race and ethnicity data were collected to inform the generalizability of the study to the wider population and to satisfy the requirements of the National Institutes of Health. From the categories provided by the National Institutes of Health, 47 participants selected White (43.5%), 42 selected Asian (38.9%) 10 selected Latinx (9.3%), 1 selected Black (1%), 1 selected Native American (1%), and 7 selected more than 1 race (6.5%). CBGT and MBSR were associated with a significant decrease in negative emotion (partial η2 range, 0.38 to 0.53) with no significant between-group differences when reacting (β, -0.04; SE, 0.09; 95% CI, -0.11 to 0.08; t92 = -0.37; P = .71), reappraising (β, -0.15; SE, 0.09; 95% CI, -0.32 to 0.03; t92 = -1.67; P = .10), or accepting (β, -0.05; SE, 0.08; 95% CI, -0.20 to 0.11; t92 = -0.59; P = .56). There was a significant increase in BOLD percentage signal change in cognitive and attention-regulation regions when reappraising (CBGT = 0.031; MBSR = 0.037) and accepting (CBGT = 0.012; MBSR = 0.077) negative self-beliefs. CBGT and MBSR did not differ in decreased negative emotion and increased reappraisal and acceptance BOLD responses. Reappraisal-associated MBSR (vs CBGT) negative emotions and CBGT (vs MBSR) brain responses were associated with social anxiety symptoms 1 year posttreatment. CONCLUSIONS AND RELEVANCE The results of this study suggest that CBGT and MBSR may be effective treatments with long-term benefits for patients with SAD that recruit cognitive and attention-regulation brain networks. Despite contrasting models of therapeutic change, CBT and MBSR may both enhance reappraisal and acceptance emotion regulation strategies. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT02036658.
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Parro C, Dixon ML, Christoff K. The neural basis of motivational influences on cognitive control. Hum Brain Mapp 2018; 39:5097-5111. [PMID: 30120846 DOI: 10.1002/hbm.24348] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [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: 08/30/2017] [Revised: 07/16/2018] [Accepted: 07/30/2018] [Indexed: 12/22/2022] Open
Abstract
Cognitive control mechanisms support the deliberate regulation of thought and behavior based on current goals. Recent work suggests that motivational incentives improve cognitive control and has begun to elucidate critical neural substrates. We conducted a quantitative meta-analysis of neuroimaging studies of motivated cognitive control using activation likelihood estimation (ALE) and Neurosynth to delineate the brain regions that are consistently activated across studies. The analysis included studies that investigated changes in brain activation during cognitive control tasks when reward incentives were present versus absent. The ALE analysis revealed consistent recruitment in regions associated with the frontoparietal control network including the inferior frontal sulcus and intraparietal sulcus, as well as regions associated with the salience network including the anterior insula and anterior mid-cingulate cortex. As a complementary analysis, we performed a large-scale exploratory meta-analysis using Neurosynth to identify regions that are recruited in studies using of the terms cognitive control and incentive. This analysis replicated the ALE results and also identified the rostrolateral prefrontal cortex, caudate nucleus, nucleus accumbens, medial thalamus, inferior frontal junction, premotor cortex, and hippocampus. Finally, we separately compared recruitment during cue and target periods, which tap into proactive engagement of rule-outcome associations, and the mobilization of appropriate viscero-motor states to execute a response, respectively. We found that largely distinct sets of brain regions are recruited during cue and target periods. Altogether, these findings suggest that flexible interactions between frontoparietal, salience, and dopaminergic midbrain-striatal networks may allow control demands to be precisely tailored based on expected value.
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Affiliation(s)
- Cameron Parro
- Department of Psychology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Matthew L Dixon
- Department of Psychology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Kalina Christoff
- Department of Psychology, University of British Columbia, Vancouver, British Columbia, Canada.,Centre for Brain Health, University of British Columbia, Vancouver, British Columbia, Canada
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Fox KCR, Andrews-Hanna JR, Mills C, Dixon ML, Markovic J, Thompson E, Christoff K. Affective neuroscience of self-generated thought. Ann N Y Acad Sci 2018; 1426:25-51. [PMID: 29754412 DOI: 10.1111/nyas.13740] [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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2017] [Revised: 03/16/2018] [Accepted: 03/28/2018] [Indexed: 01/05/2023]
Abstract
Despite increasing scientific interest in self-generated thought-mental content largely independent of the immediate environment-there has yet to be any comprehensive synthesis of the subjective experience and neural correlates of affect in these forms of thinking. Here, we aim to develop an integrated affective neuroscience encompassing many forms of self-generated thought-normal and pathological, moderate and excessive, in waking and in sleep. In synthesizing existing literature on this topic, we reveal consistent findings pertaining to the prevalence, valence, and variability of emotion in self-generated thought, and highlight how these factors might interact with self-generated thought to influence general well-being. We integrate these psychological findings with recent neuroimaging research, bringing attention to the neural correlates of affect in self-generated thought. We show that affect in self-generated thought is prevalent, positively biased, highly variable (both within and across individuals), and consistently recruits many brain areas implicated in emotional processing, including the orbitofrontal cortex, amygdala, insula, and medial prefrontal cortex. Many factors modulate these typical psychological and neural patterns, however; the emerging affective neuroscience of self-generated thought must endeavor to link brain function and subjective experience in both everyday self-generated thought as well as its dysfunctions in mental illness.
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Affiliation(s)
- Kieran C R Fox
- Department of Neurology and Neurological Sciences, Stanford University, Stanford, California
- Department of Psychology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Jessica R Andrews-Hanna
- Department of Psychology and Interdisciplinary Program in Cognitive Science, University of Arizona, Tucson, Arizona
| | - Caitlin Mills
- Department of Psychology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Matthew L Dixon
- Department of Psychology, University of British Columbia, Vancouver, British Columbia, Canada
- Department of Psychology, University of Toronto, Toronto, Ontario, Canada
| | - Jelena Markovic
- Department of Philosophy, University of British Columbia, Vancouver, British Columbia, Canada
| | - Evan Thompson
- Department of Philosophy, University of British Columbia, Vancouver, British Columbia, Canada
| | - Kalina Christoff
- Department of Psychology, University of British Columbia, Vancouver, British Columbia, Canada
- Centre for Brain Health, University of British Columbia, Vancouver, British Columbia, Canada
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Ellamil M, Fox KCR, Dixon ML, Pritchard S, Todd RM, Thompson E, Christoff K. Dynamics of neural recruitment surrounding the spontaneous arising of thoughts in experienced mindfulness practitioners. Neuroimage 2016; 136:186-96. [PMID: 27114056 DOI: 10.1016/j.neuroimage.2016.04.034] [Citation(s) in RCA: 87] [Impact Index Per Article: 10.9] [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: 12/22/2015] [Revised: 04/12/2016] [Accepted: 04/14/2016] [Indexed: 01/17/2023] Open
Abstract
Thoughts arise spontaneously in our minds with remarkable frequency, but tracking the brain systems associated with the early inception of a thought has proved challenging. Here we addressed this issue by taking advantage of the heightened introspective ability of experienced mindfulness practitioners to observe the onset of their spontaneously arising thoughts. We found subtle differences in timing among the many regions typically recruited by spontaneous thought. In some of these regions, fMRI signal peaked prior to the spontaneous arising of a thought - most notably in the medial temporal lobe and inferior parietal lobule. In contrast, activation in the medial prefrontal, temporopolar, mid-insular, lateral prefrontal, and dorsal anterior cingulate cortices peaked together with or immediately following the arising of spontaneous thought. We propose that brain regions that show antecedent recruitment may be preferentially involved in the initial inception of spontaneous thoughts, while those that show later recruitment may be preferentially involved in the subsequent elaboration and metacognitive processing of spontaneous thoughts. Our findings highlight the temporal dynamics of neural recruitment surrounding the emergence of spontaneous thoughts and may help account for some of spontaneous thought's peculiar qualities, including its wild diversity of content and its links to memory and attention.
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Affiliation(s)
- Melissa Ellamil
- Department of Psychology, University of British Columbia, 2136 West Mall, Vancouver, British Columbia V6T 1Z4, Canada
| | - Kieran C R Fox
- Department of Psychology, University of British Columbia, 2136 West Mall, Vancouver, British Columbia V6T 1Z4, Canada
| | - Matthew L Dixon
- Department of Psychology, University of British Columbia, 2136 West Mall, Vancouver, British Columbia V6T 1Z4, Canada
| | - Sean Pritchard
- School of Psychology, Fielding Graduate University, 2020 De la Vina Street, Santa Barbara, CA 93105, United States
| | - Rebecca M Todd
- Department of Psychology, University of British Columbia, 2136 West Mall, Vancouver, British Columbia V6T 1Z4, Canada; Centre for Brain Health, University of British Columbia, 2215 Wesbrook Mall, Vancouver, British Columbia V6T 1Z3, Canada
| | - Evan Thompson
- Department of Philosophy, University of British Columbia, 1866 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada
| | - Kalina Christoff
- Department of Psychology, University of British Columbia, 2136 West Mall, Vancouver, British Columbia V6T 1Z4, Canada; Centre for Brain Health, University of British Columbia, 2215 Wesbrook Mall, Vancouver, British Columbia V6T 1Z3, Canada.
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Fox KCR, Dixon ML, Nijeboer S, Girn M, Floman JL, Lifshitz M, Ellamil M, Sedlmeier P, Christoff K. Functional neuroanatomy of meditation: A review and meta-analysis of 78 functional neuroimaging investigations. Neurosci Biobehav Rev 2016; 65:208-28. [PMID: 27032724 DOI: 10.1016/j.neubiorev.2016.03.021] [Citation(s) in RCA: 220] [Impact Index Per Article: 27.5] [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: 10/07/2015] [Revised: 02/25/2016] [Accepted: 03/01/2016] [Indexed: 12/19/2022]
Abstract
Meditation is a family of mental practices that encompasses a wide array of techniques employing distinctive mental strategies. We systematically reviewed 78 functional neuroimaging (fMRI and PET) studies of meditation, and used activation likelihood estimation to meta-analyze 257 peak foci from 31 experiments involving 527 participants. We found reliably dissociable patterns of brain activation and deactivation for four common styles of meditation (focused attention, mantra recitation, open monitoring, and compassion/loving-kindness), and suggestive differences for three others (visualization, sense-withdrawal, and non-dual awareness practices). Overall, dissociable activation patterns are congruent with the psychological and behavioral aims of each practice. Some brain areas are recruited consistently across multiple techniques-including insula, pre/supplementary motor cortices, dorsal anterior cingulate cortex, and frontopolar cortex-but convergence is the exception rather than the rule. A preliminary effect-size meta-analysis found medium effects for both activations (d=0.59) and deactivations (d=-0.74), suggesting potential practical significance. Our meta-analysis supports the neurophysiological dissociability of meditation practices, but also raises many methodological concerns and suggests avenues for future research.
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Affiliation(s)
- Kieran C R Fox
- Department of Psychology, University of British Columbia, 2136 West Mall, Vancouver, B.C., V6T 1Z4, Canada.
| | - Matthew L Dixon
- Department of Psychology, University of British Columbia, 2136 West Mall, Vancouver, B.C., V6T 1Z4, Canada
| | - Savannah Nijeboer
- Department of Psychology, University of British Columbia, 2136 West Mall, Vancouver, B.C., V6T 1Z4, Canada
| | - Manesh Girn
- Department of Psychology, University of British Columbia, 2136 West Mall, Vancouver, B.C., V6T 1Z4, Canada
| | - James L Floman
- Department of Educational and Counselling Psychology, and Special Education, University of British Columbia, 2125 Main Mall, Vancouver, B.C., V6T 1Z4, Canada
| | - Michael Lifshitz
- Integrated Program in Neuroscience, McGill University, 3775 University St., Montreal, QC, H3A 2B4, Canada
| | - Melissa Ellamil
- Neuroanatomy and Connectivity Research Group, Max Planck Institute for Human Cognitive and Brain Sciences, Stephanstrasse 1a, Leipzig, 04103, Germany
| | - Peter Sedlmeier
- Institut für Psychologie, Technische Universität Chemnitz, 43 Wilhelm-Raabe Street, Chemnitz, Germany
| | - Kalina Christoff
- Department of Psychology, University of British Columbia, 2136 West Mall, Vancouver, B.C., V6T 1Z4, Canada; Brain Research Centre, University of British Columbia, 2211 Wesbrook Mall, Vancouver, B.C., V6T 2B5, Canada
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Affiliation(s)
- Matthew L Dixon
- Department of Psychology, Cognitive Neuroscience of Thought Laboratory, University of British Columbia Vancouver, BC, Canada
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Dixon ML, Fox KC, Christoff K. A framework for understanding the relationship between externally and internally directed cognition. Neuropsychologia 2014; 62:321-30. [DOI: 10.1016/j.neuropsychologia.2014.05.024] [Citation(s) in RCA: 104] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2013] [Revised: 04/27/2014] [Accepted: 05/24/2014] [Indexed: 10/25/2022]
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Dixon ML, Fox KC, Christoff K. Evidence for rostro-caudal functional organization in multiple brain areas related to goal-directed behavior. Brain Res 2014; 1572:26-39. [DOI: 10.1016/j.brainres.2014.05.012] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2014] [Revised: 05/01/2014] [Accepted: 05/10/2014] [Indexed: 12/01/2022]
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Schmitz TW, Dixon ML, Anderson AK, De Rosa E. Distinguishing attentional gain and tuning in young and older adults. Neurobiol Aging 2014; 35:2514-2525. [PMID: 24906891 DOI: 10.1016/j.neurobiolaging.2014.04.028] [Citation(s) in RCA: 17] [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: 11/30/2012] [Revised: 04/23/2014] [Accepted: 04/27/2014] [Indexed: 11/16/2022]
Abstract
Here we examined with functional magnetic resonance imaging (fMRI) whether advanced age affects 2 mechanisms of attention that are widely thought to enhance signal processing in the sensory neocortex: gain and tuning. Healthy young and older adults discriminated faces under varying levels of object competition while fMRI was acquired. In young adults, cortical response magnitude to attended faces was maintained despite increasing competition, consistent with gain. Cortical response selectivity, indexed from repetition suppression, also increased only for attended faces despite increasing competition, consistent with tuning. Older adults exhibited intact gain, but altered tuning, with extrastriate cortical tuning determined by object salience rather than attention. Moreover, the magnitude of this susceptibility to stimulus-driven processing was associated with a redistribution of attention-driven competitive processes to the frontal cortices. These data indicate that although both gain and tuning are modulated by increased perceptual competition, they are functionally dissociable in the extrastriate cortices, exhibit differential susceptibility to advanced aging, and spare the frontal cortices a considerable processing burden through early selection.
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Affiliation(s)
- Taylor W Schmitz
- Department of Psychology, University of Toronto, Toronto, Ontario, Canada; Collaborative Program in Neuroscience, University of Toronto, Toronto, Ontario, Canada.
| | - Matthew L Dixon
- Department of Psychology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Adam K Anderson
- Department of Psychology, University of Toronto, Toronto, Ontario, Canada; Collaborative Program in Neuroscience, University of Toronto, Toronto, Ontario, Canada; Rotman Research Institute of Baycrest Centre, Toronto, Ontario, Canada
| | - Eve De Rosa
- Department of Psychology, University of Toronto, Toronto, Ontario, Canada; Collaborative Program in Neuroscience, University of Toronto, Toronto, Ontario, Canada; Rotman Research Institute of Baycrest Centre, Toronto, Ontario, Canada.
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Dixon ML, Christoff K. The decision to engage cognitive control is driven by expected reward-value: neural and behavioral evidence. PLoS One 2012; 7:e51637. [PMID: 23284730 PMCID: PMC3526643 DOI: 10.1371/journal.pone.0051637] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [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: 07/04/2012] [Accepted: 11/02/2012] [Indexed: 11/30/2022] Open
Abstract
Cognitive control is a fundamental skill reflecting the active use of task-rules to guide behavior and suppress inappropriate automatic responses. Prior work has traditionally used paradigms in which subjects are told when to engage cognitive control. Thus, surprisingly little is known about the factors that influence individuals' initial decision of whether or not to act in a reflective, rule-based manner. To examine this, we took three classic cognitive control tasks (Stroop, Wisconsin Card Sorting Task, Go/No-Go task) and created novel ‘free-choice’ versions in which human subjects were free to select an automatic, pre-potent action, or an action requiring rule-based cognitive control, and earned varying amounts of money based on their choices. Our findings demonstrated that subjects' decision to engage cognitive control was driven by an explicit representation of monetary rewards expected to be obtained from rule-use. Subjects rarely engaged cognitive control when the expected outcome was of equal or lesser value as compared to the value of the automatic response, but frequently engaged cognitive control when it was expected to yield a larger monetary outcome. Additionally, we exploited fMRI-adaptation to show that the lateral prefrontal cortex (LPFC) represents associations between rules and expected reward outcomes. Together, these findings suggest that individuals are more likely to act in a reflective, rule-based manner when they expect that it will result in a desired outcome. Thus, choosing to exert cognitive control is not simply a matter of reason and willpower, but rather, conforms to standard mechanisms of value-based decision making. Finally, in contrast to current models of LPFC function, our results suggest that the LPFC plays a direct role in representing motivational incentives.
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Affiliation(s)
- Matthew L Dixon
- Department of Psychology, University of British Columbia, Vancouver, British Columbia, Canada.
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Abstract
Visual scenes contain many statistical regularities such as the likely identity and location of objects that are present; with experience, such regularities can be encoded and can ultimately facilitate the deployment of spatial attention to important locations. Memory-guided attention has been extensively examined in adults with the 'contextual cueing' paradigm and has been linked to specific neural substrates - a medial temporal lobe (MTL)-frontoparietal network. However, it currently remains unknown when this ability comes 'online' during development. Thus, we examined the performance of school-aged children on an age-appropriate version of the contextual cueing paradigm. Children searched for a target fish among distractor fish in new displays and in 'old' displays on a touchscreen computer. Old displays repeated across blocks of trials and thus provided an opportunity for prior experience with the invariant configuration of the stimuli to guide attentional deployment. We found that over time children searched old displays significantly faster than new displays, thus revealing intact memory-guided attention and presumed function of an MTL-frontoparietal network in 5- to 9-year-olds. More generally, our findings suggest that children are remarkably sensitive to the inherent structure of their visual environment and this enables attentional deployment to become more efficient with experience.
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Affiliation(s)
- Matthew L Dixon
- Department of Psychology, University of Toronto, 100 Saint George Street, Toronto, ON, Canada, M5S 3G3
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Abstract
Mutation, recombination, and mitochondrial deficiencies have been proposed to have roles in the carcinogenic process. We describe a diploid strain of the yeast Saccharomyces cerevisiae capable of detecting this wide spectrum of genetic changes. Strain XD83 can detect forward mutation, back nuclear frameshift and base-pair substitution mutation, nuclear intragenic and intergenic recombination, and mitochondrial forward point mutations and deletions. The markers used for monitoring these events have been especially well characterized genetically. Ultraviolet light was chosen as a model carcinogenic agent to test this system. In addition to highly significant (P less than 0.01) increases in the frequencies of each genetic change, increases in the absolute numbers (yields) of each change indicated induction and not selective survival. The relative amounts of each type of genetic change varied with dose and should be considered a part of the spectrum of change induced by ultraviolet light. The wide spectrum of endpoints monitored in the XD83 yeast system may allow the detection of certain carcinogens and other genetically toxic agents which have escaped detection in more limited systems. Since only one strain is required to simultaneously monitor these genetic changes, this assay system should facilitate comparisons of the induced changes and be more efficient than using multiple strains to monitor the same endpoints.
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