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Articles 61 - 90 of 129

Full-Text Articles in Neuroscience and Neurobiology

Reconstructing Representations Of Dynamic Visual Objects In Early Visual Cortex, Edmund Chong, Ariana M. Familiar, Won Mok Shim Feb 2016

Reconstructing Representations Of Dynamic Visual Objects In Early Visual Cortex, Edmund Chong, Ariana M. Familiar, Won Mok Shim

Dartmouth Scholarship

As raw sensory data are partial, our visual system extensively fills in missing details, creating enriched percepts based on incomplete bottom-up information. Despite evidence for internally generated representations at early stages of cortical processing, it is not known whether these representations include missing information of dynamically transforming objects. Long-range apparent motion (AM) provides a unique test case because objects in AM can undergo changes both in position and in features. Using fMRI and encoding methods, we found that the “intermediate” orientation of an apparently rotating grating, never presented in the retinal input but interpolated during AM, is reconstructed in population-level, …

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Neuron Morphology Influences Axon Initial Segment Plasticity, Allan T. Gulledge, Jaime J. Bravo Jan 2016

Neuron Morphology Influences Axon Initial Segment Plasticity, Allan T. Gulledge, Jaime J. Bravo

Dartmouth Scholarship

In most vertebrate neurons, action potentials are initiated in the axon initial segment (AIS), a specialized region of the axon containing a high density of voltage-gated sodium and potassium channels. It has recently been proposed that neurons use plasticity of AIS length and/or location to regulate their intrinsic excitability. Here we quantify the impact of neuron morphology on AIS plasticity using computational models of simplified and realistic somatodendritic morphologies. In small neurons (e.g., dentate granule neurons), excitability was highest when the AIS was of intermediate length and located adjacent to the soma. Conversely, neurons having larger dendritic trees (e.g., pyramidal …

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Isoflurane Inhibits Synaptic Vesicle Exocytosis Through Reduced Ca2+ Influx, Not Ca2+-Exocytosis Coupling, Joel Baumgart, Zhen-Yu Zhou, Masato Hara, Daniel Cook, Michael Hoppa Sep 2015

Isoflurane Inhibits Synaptic Vesicle Exocytosis Through Reduced Ca2+ Influx, Not Ca2+-Exocytosis Coupling, Joel Baumgart, Zhen-Yu Zhou, Masato Hara, Daniel Cook, Michael Hoppa

Dartmouth Scholarship

Identifying presynaptic mechanisms of general anesthetics is critical to understanding their effects on synaptic transmission. We show that the volatile anesthetic isoflurane inhibits synaptic vesicle (SV) exocytosis at nerve terminals in dissociated rat hippocampal neurons through inhibition of presynaptic Ca2+ influx without significantly altering the Ca2+ sensitivity of SV exocytosis. A clinically relevant concentration of isoflurane (0.7 mM) inhibited changes in [Ca2+]i driven by single action potentials (APs) by 25 ± 3%, which in turn led to 62 ± 3% inhibition of single AP-triggered exocytosis at 4 mM extracellular Ca2+ ([Ca2+]e). Lowering external Ca2+ to match the isoflurane-induced reduction in …

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Familiar Face Detection In 180ms, Matteo Visconti Di Oleggio Castello, M. Ida Gobbini Aug 2015

Familiar Face Detection In 180ms, Matteo Visconti Di Oleggio Castello, M. Ida Gobbini

Dartmouth Scholarship

The visual system is tuned for rapid detection of faces, with the fastest choice saccade to a face at 100ms. Familiar faces have a more robust representation than do unfamiliar faces, and are detected faster in the absence of awareness and with reduced attentional resources. Faces of family and close friends become familiar over a protracted period involving learning the unique visual appearance, including a view-invariant representation, as well as person knowledge. We investigated the effect of personal familiarity on the earliest stages of face processing by using a saccadic-choice task to measure how fast familiar face detection can happen. …

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Prenatal Predictors Of Infant Self-Regulation: The Contributions Of Placental Dna Methylation Of Nr3c1 And Neuroendocrine Activity, Elisabeth Conradt, Mary Fei, Linda Lagasse, Edward Tronick, Dylan Guerin, Daniel Gorman, Carmen J. Marsit, Barry M. Lester May 2015

Prenatal Predictors Of Infant Self-Regulation: The Contributions Of Placental Dna Methylation Of Nr3c1 And Neuroendocrine Activity, Elisabeth Conradt, Mary Fei, Linda Lagasse, Edward Tronick, Dylan Guerin, Daniel Gorman, Carmen J. Marsit, Barry M. Lester

Dartmouth Scholarship

We examined whether placental DNA methylation of the glucocorticoid receptor gene, NR3C1 was associated with self-regulation and neuroendocrine responses to a social stressor in infancy. Placenta samples were obtained at birth and mothers and their infants (n = 128) participated in the still-face paradigm when infants were 5 months old. Infant self-regulation following the still-face episode was coded and pre-stress cortisol and cortisol reactivity was assessed in response to the still-face paradigm. A factor analysis of NR3C1 CpG sites revealed two factors: one for CpG sites 1-4 and the other for sites 5-13. DNA methylation of the factor comprising NR3C1 …

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Axonal Activity In Vivo: Technical Considerations And Implications For The Exploration Of Neural Circuits In Freely Moving Animals, Jeremy M. Barry May 2015

Axonal Activity In Vivo: Technical Considerations And Implications For The Exploration Of Neural Circuits In Freely Moving Animals, Jeremy M. Barry

Dartmouth Scholarship

While extracellular somatic action potentials from freely moving rats have been well characterized, axonal activity has not. We have recently reported extracellular tetrode recordings of short duration waveforms (SDWs) with an average peak-trough duration less than 172μs. These waveforms have significantly shorter duration than somatic action potentials and tend to be triphasic. The present review discusses further data that suggests SDWs are representative of axonal activity, how this characterization allows for more accurate classification of somatic activity and could serve as a means of exploring signal integration in neural circuits. The review also discusses how axons may function as more …

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Multimodal Frontostriatal Connectivity Underlies Individual Differences In Self-Esteem, Robert S. Chavez, Todd F. Heatherton May 2015

Multimodal Frontostriatal Connectivity Underlies Individual Differences In Self-Esteem, Robert S. Chavez, Todd F. Heatherton

Dartmouth Scholarship

A heightened sense of self-esteem is associated with a reduced risk for several types of affective and psychiatric disorders, including depression, anxiety and eating disorders. However, little is known about how brain systems integrate self-referential processing and positive evaluation to give rise to these feelings. To address this, we combined diffusion tensor imaging (DTI) and functional magnetic resonance imaging (fMRI) to test how frontostriatal connectivity reflects long-term trait and short-term state aspects of self-esteem. Using DTI, we found individual variability in white matter structural integrity between the medial prefrontal cortex and the ventral striatum was related to trait measures of …

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Retrosplenial Cortex And Long-Term Memory: Molecules To Behavior, Travis P. Todd, David J. Bucci Mar 2015

Retrosplenial Cortex And Long-Term Memory: Molecules To Behavior, Travis P. Todd, David J. Bucci

Dartmouth Scholarship

The retrosplenial cortex (RSC) is reciprocally connected with the hippocampus and various parahippocampal cortical regions, suggesting that RSC is well-positioned to contribute to hippocampal-dependent memory. Consistent with this, substantial behavioral evidence indicates that RSC is essential for consolidating and/or retrieving contextual and spatial memories. In addition, there is growing evidence that RSC neurons undergo activity-dependent plastic changes during memory formation and retrieval. In this paper we review both the behavioral and cellular/molecular data and posit that the RSC has a particularly important role in the storage and retrieval of spatial and contextual memories perhaps due its involvement in binding together …

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Belief About Nicotine Selectively Modulates Value And Reward Prediction Error Signals In Smokers, Xiaosi Gu, Terry Lohrenz, Ramiro Salas, Philip R. Baldwin, Alireza Soltani Feb 2015

Belief About Nicotine Selectively Modulates Value And Reward Prediction Error Signals In Smokers, Xiaosi Gu, Terry Lohrenz, Ramiro Salas, Philip R. Baldwin, Alireza Soltani

Dartmouth Scholarship

Little is known about how prior beliefs impact biophysically described processes in the presence of neuroactive drugs, which presents a profound challenge to the understanding of the mechanisms and treatments of addiction. We engineered smokers' prior beliefs about the presence of nicotine in a cigarette smoked before a functional magnetic resonance imaging session where subjects carried out a sequential choice task. Using a model-based approach, we show that smokers' beliefs about nicotine specifically modulated learning signals (value and reward prediction error) defined by a computational model of mesolimbic dopamine systems. Belief of "no nicotine in cigarette" (compared with "nicotine in …

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Modeling Neurovascular Coupling From Clustered Parameter Sets For Multimodal Eeg-Nirs, M. Tanveer Talukdar, H. Robert Frost, Solomon G. G. Diamond Feb 2015

Modeling Neurovascular Coupling From Clustered Parameter Sets For Multimodal Eeg-Nirs, M. Tanveer Talukdar, H. Robert Frost, Solomon G. G. Diamond

Dartmouth Scholarship

Despite significant improvements in neuroimaging technologies and analysis methods, the fundamental relationship between local changes in cerebral hemodynamics and the underlying neural activity remains largely unknown. In this study, a data driven approach is proposed for modeling this neurovascular coupling relationship from simultaneously acquired electroencephalographic (EEG) and near-infrared spectroscopic (NIRS) data. The approach uses gamma transfer functions to map EEG spectral envelopes that reflect time-varying power variations in neural rhythms to hemodynamics measured with NIRS during median nerve stimulation. The approach is evaluated first with simulated EEG-NIRS data and then by applying the method to experimental EEG-NIRS data measured from …

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Exposure To Kynurenic Acid During Adolescence Increases Sign-Tracking And Impairs Long-Term Potentiation In Adulthood, Nicole E. Deangeli, Travis P. Todd, Stephen E. Chang, Hermes H. Yeh, Pamela W. Yeh, David J. Bucci Jan 2015

Exposure To Kynurenic Acid During Adolescence Increases Sign-Tracking And Impairs Long-Term Potentiation In Adulthood, Nicole E. Deangeli, Travis P. Todd, Stephen E. Chang, Hermes H. Yeh, Pamela W. Yeh, David J. Bucci

Dartmouth Scholarship

Changes in brain reward systems are thought to contribute significantly to the cognitive and behavioral impairments of schizophrenia, as well as the propensity to develop co-occurring substance abuse disorders. Presently, there are few treatments for persons with a dual diagnosis and little is known about the neural substrates that underlie co-occurring schizophrenia and substance abuse. One goal of the present study was to determine if a change in the concentration of kynurenic acid (KYNA), a tryptophan metabolite that is increased in the brains of people with schizophrenia, affects reward-related behavior. KYNA is an endogenous antagonist of NMDA glutamate receptors and …

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Functional And Developmental Identification Of A Molecular Subtype Of Brain Serotonergic Neuron Specialized To Regulate Breathing Dynamics, Rachael D. Brust, Andrea E. Corcoran, George B. Richerson, Eugene Nattie, Susan M. Dymecki Dec 2014

Functional And Developmental Identification Of A Molecular Subtype Of Brain Serotonergic Neuron Specialized To Regulate Breathing Dynamics, Rachael D. Brust, Andrea E. Corcoran, George B. Richerson, Eugene Nattie, Susan M. Dymecki

Dartmouth Scholarship

Serotonergic neurons modulate behavioral and physiological responses from aggression and anxiety to breathing and thermoregulation. Disorders involving serotonin (5HT) dysregulation are commensurately heterogeneous and numerous. We hypothesized that this breadth in functionality derives in part from a developmentally determined substructure of distinct subtypes of 5HT neurons each specialized to modulate specific behaviors. By manipulating developmentally defined subgroups one by one chemogenetically, we find that the Egr2-Pet1 subgroup is specialized to drive increased ventilation in response to carbon dioxide elevation and acidosis. Furthermore, this subtype exhibits intrinsic chemosensitivity and modality-specific projections-increasing firing during hypercapnic acidosis and selectively projecting to respiratory chemosensory …

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Dissociation Between Face Perception And Face Memory In Adults, But Not Children, With Developmental Prosopagnosia, Kirsten A. Dalrymple, Lúcia Garrido, Brad Duchaine Oct 2014

Dissociation Between Face Perception And Face Memory In Adults, But Not Children, With Developmental Prosopagnosia, Kirsten A. Dalrymple, Lúcia Garrido, Brad Duchaine

Dartmouth Scholarship

Cognitive models propose that face recognition is accomplished through a series of discrete stages, including perceptual representation of facial structure, and encoding and retrieval of facial information. This implies that impaired face recognition can result from failures of face perception, face memory, or both. Studies of acquired prosopagnosia, autism spectrum disorders, and the development of normal face recognition support the idea that face perception and face memory are distinct processes, yet this distinction has received little attention in developmental prosopagnosia (DP). To address this issue, we tested the face perception and face memory of children and adults with DP. By …

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Activity-Dependent Serotonergic Excitation Of Callosal Projection Neurons In The Mouse Prefrontal Cortex, Emily K. Stephens, Daniel Avesar, Allan T. Gulledge Aug 2014

Activity-Dependent Serotonergic Excitation Of Callosal Projection Neurons In The Mouse Prefrontal Cortex, Emily K. Stephens, Daniel Avesar, Allan T. Gulledge

Dartmouth Scholarship

Layer 5 pyramidal neurons (L5PNs) in the mouse prefrontal cortex respond to serotonin (5-HT) according to their long-distance axonal projections; 5-HT1A (1A) receptors mediate inhibitory responses in corticopontine (CPn) L5PNs, while 5-HT2A (2A) receptors can enhance action potential (AP) output in callosal/commissural (COM) L5PNs, either directly (in “COM-excited” neurons), or following brief 1A-mediated inhibition (in “COM-biphasic” neurons). Here we compare the impact of 5-HT on the excitability of CPn and COM L5PNs experiencing variable excitatory drive produced by current injection (DC current or simulated synaptic current) or with exogenous glutamate. 5-HT delivered at resting membrane potentials, or paired …

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What Can Individual Differences Reveal About Face Processing?, Galit Yovel, Jeremy B. Wilmer, Brad Duchaine Aug 2014

What Can Individual Differences Reveal About Face Processing?, Galit Yovel, Jeremy B. Wilmer, Brad Duchaine

Dartmouth Scholarship

Faces are probably the most widely studied visual stimulus. Most research on face processing has used a group-mean approach that averages behavioral or neural responses to faces across individuals and treats variance between individuals as noise. However, individual differences in face processing can provide valuable information that complements and extends findings from group-mean studies. Here we demonstrate that studies employing an individual differences approach—examining associations and dissociations across individuals—can answer fundamental questions about the way face processing operates. In particular these studies allow us to associate and dissociate the mechanisms involved in face processing, tie behavioral face processing mechanisms to …

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Unconscious Neural Processing Differs With Method Used To Render Stimuli Invisible, Sergey V. Fogelson, Peter J. Kohler, Kevin J. Miller, Richard Granger, Peter U. Tse Jun 2014

Unconscious Neural Processing Differs With Method Used To Render Stimuli Invisible, Sergey V. Fogelson, Peter J. Kohler, Kevin J. Miller, Richard Granger, Peter U. Tse

Dartmouth Scholarship

Visual stimuli can be kept from awareness using various methods. The extent of processing that a given stimulus receives in the absence of awareness is typically used to make claims about the role of consciousness more generally. The neural processing elicited by a stimulus, however, may also depend on the method used to keep it from awareness, and not only on whether the stimulus reaches awareness. Here we report that the method used to render an image invisible has a dramatic effect on how category information about the unseen stimulus is encoded across the human brain. We collected fMRI data …

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Online Tracking Of The Contents Of Conscious Perception Using Real-Time Fmri, Christoph Reichert, Robert Fendrich, Johannes Bernarding, Claus Tempelmann, Hermann Hinrichs, Jochem W. Rieger May 2014

Online Tracking Of The Contents Of Conscious Perception Using Real-Time Fmri, Christoph Reichert, Robert Fendrich, Johannes Bernarding, Claus Tempelmann, Hermann Hinrichs, Jochem W. Rieger

Dartmouth Scholarship

Perception is an active process that interprets and structures the stimulus input based on assumptions about its possible causes. We use real-time functional magnetic resonance imaging (rtfMRI) to investigate a particularly powerful demonstration of dynamic object integration in which the same physical stimulus intermittently elicits categorically different conscious object percepts. In this study, we simulated an outline object that is moving behind a narrow slit. With such displays, the physically identical stimulus can elicit categorically different percepts that either correspond closely to the physical stimulus (vertically moving line segments) or represent a hypothesis about the underlying cause of the physical …

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Fatty Acids Increase Neuronal Hypertrophy Of Pten Knockdown Neurons, Catherine J. Fricano, Tyrone Despenza, Paul W. Frazel, Meijie Li, A. James O'Malley, Gary Westbrook, Bryan Luikart Apr 2014

Fatty Acids Increase Neuronal Hypertrophy Of Pten Knockdown Neurons, Catherine J. Fricano, Tyrone Despenza, Paul W. Frazel, Meijie Li, A. James O'Malley, Gary Westbrook, Bryan Luikart

Dartmouth Scholarship

Phosphatase and tensin homolog (Pten) catalyzes the reverse reaction of PI3K by dephosphorylating PIP3 to PIP2. This negatively regulates downstream Akt/mTOR/S6 signaling resulting in decreased cellular growth and proliferation. Co-injection of a lentivirus knocking Pten down with a control lentivirus allows us to compare the effects of Pten knockdown between individual neurons within the same animal. We find that knockdown of Pten results in neuronal hypertrophy by 21 days post-injection. This neuronal hypertrophy is correlated with increased p-S6 and p-mTOR in individual neurons. We used this system to test whether an environmental factor that has been implicated in cellular hypertrophy …

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Movement-Based Embodied Contemplative Practices: Definitions And Paradigms, Laura Schmalzl, Mardi A. Crane-Godreau, Peter Payne Apr 2014

Movement-Based Embodied Contemplative Practices: Definitions And Paradigms, Laura Schmalzl, Mardi A. Crane-Godreau, Peter Payne

Dartmouth Scholarship

Over the past decades, cognitive neuroscience has witnessed a shift from predominantly disembodied and computational views of the mind, to more embodied and situated views of the mind. These postulate that mental functions cannot be fully understood without reference to the physical body and the environment in which they are experienced. Within the field of contemplative science, the directing of attention to bodily sensations has so far mainly been studied in the context of seated meditation and mindfulness practices. However, the cultivation of interoceptive, proprioceptive and kinesthetic awareness is also said to lie at the core of many movement-based contemplative …

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Normal Acquisition Of Expertise With Greebles In Two Cases Of Acquired Prosopagnosia, Constantin Rezlescu, Jason J. S. Barton, David Pitcher, Bradley Duchaine Apr 2014

Normal Acquisition Of Expertise With Greebles In Two Cases Of Acquired Prosopagnosia, Constantin Rezlescu, Jason J. S. Barton, David Pitcher, Bradley Duchaine

Dartmouth Scholarship

Face recognition is generally thought to rely on different neurocognitive mechanisms than most types of objects, but the specificity of these mechanisms is debated. One account suggests the mechanisms are specific to upright faces, whereas the expertise view proposes the mechanisms operate on objects of high within-class similarity with which an observer has become proficient at rapid individuation. Much of the evidence cited in support of the expertise view comes from laboratory-based training experiments involving computer-generated objects called greebles that are designed to place face-like demands on recognition mechanisms. A fundamental prediction of the expertise hypothesis is that recognition deficits …

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The N400 As An Index Of Racial Stereotype Accessibility, Eric Hehman, Hannah I. Volpert, Robert F. Simons Mar 2014

The N400 As An Index Of Racial Stereotype Accessibility, Eric Hehman, Hannah I. Volpert, Robert F. Simons

Dartmouth Scholarship

The current research examined the viability of the N400, an event-related potential (ERP) related to the detection of semantic incongruity, as an index of both stereotype accessibility and interracial prejudice. Participants’ EEG was recorded while they completed a sequential priming task, in which negative or positive, stereotypically black (African American) or white (Caucasian American) traits followed the presentation of either a black or white face acting as a prime. ERP examination focused on the N400, but additionally examined N100 and P200 reactivity. Replicating and extending previous N400 stereotype research, results indicated that the N400 can indeed function as an index …

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Exploring Emotions Using Invasive Methods: Review Of 60 Years Of Human Intracranial Electrophysiology, Sean A. Guillory, Krzysztof A. Bujarski Mar 2014

Exploring Emotions Using Invasive Methods: Review Of 60 Years Of Human Intracranial Electrophysiology, Sean A. Guillory, Krzysztof A. Bujarski

Dartmouth Scholarship

Over the past 60 years, human intracranial electrophysiology (HIE) has been used to characterize seizures in patients with epilepsy. Secondary to the clinical objectives, electrodes implanted intracranially have been used to investigate mechanisms of human cognition. In addition to studies of memory and language, HIE methods have been used to investigate emotions. The aim of this review is to outline the contribution of HIE (electrocorticography, single-unit recording and electrical brain stimulation) to our understanding of the neural representations of emotions. We identified 64 papers dating back to the mid-1950s which used HIE techniques to study emotional states. Evidence from HIE …

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Investigating Habits: Strategies,Technologies And Models, Kyle S. Smith, Ann M. Graybiel Feb 2014

Investigating Habits: Strategies,Technologies And Models, Kyle S. Smith, Ann M. Graybiel

Dartmouth Scholarship

Understanding habits at a biological level requires a combination of behavioral observations and measures of ongoing neural activity. Theoretical frameworks as well as definitions of habitual behaviors emerging from classic behavioral research have been enriched by new approaches taking account of the identification of brain regions and circuits related to habitual behavior. Together, this combination of experimental and theoretical work has provided key insights into how brain circuits underlying action-learning and action-selection are organized, and how a balance between behavioral flexibility and fixity is achieved. New methods to monitor and manipulate neural activity in real time are allowing us to …

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The Mammalian Neocortex New Pyramidal Neuron: A New Conception, Miguel Marín-Padilla Jan 2014

The Mammalian Neocortex New Pyramidal Neuron: A New Conception, Miguel Marín-Padilla

Dartmouth Scholarship

The new cerebral cortex (neocortex) and the new type of pyramidal neuron are mammalian innovations that have evolved for operating their increasing motor capabilities while essentially using analogous anatomical and neural makeups. The human neocortex starts to develop in 6-week-old embryos with the establishment of a primordial cortical organization, which resembles the primitive cortices of amphibian and reptiles. From the 8th to the 15th week of age, new pyramidal neurons, of ependymal origin, are progressively incorporated within this primordial cortex forming a cellular plate that divides its components into those above it (neocortex first layer) and those below it (neocortex …

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Enrichment And Training Improve Cognition In Rats With Cortical Malformations, Kyle R. Jenks, Marcella M. Lucas, Ben A. Duffy, Ashlee A. Robbins, Barjor Gimi, Jeremy M. Barry, Rod C. Scott Dec 2013

Enrichment And Training Improve Cognition In Rats With Cortical Malformations, Kyle R. Jenks, Marcella M. Lucas, Ben A. Duffy, Ashlee A. Robbins, Barjor Gimi, Jeremy M. Barry, Rod C. Scott

Dartmouth Scholarship

Children with malformations of cortical development (MCD) frequently have associated cognitive impairments which reduce quality of life. We hypothesized that cognitive deficits associated with MCD can be improved with environmental manipulation or additional training. The E17 methylazoxymethanol acetate (MAM) exposure model bears many anatomical hallmarks seen in human MCDs as well as similar behavioral and cognitive deficits. We divided control and MAM exposed Sprague-Dawley rats into enriched and non-enriched groups and tested performance in the Morris water maze. Another group similarly divided underwent sociability testing and also underwent Magnetic Resonance Imaging (MRI) scans pre and post enrichment. A third group …

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On The Evolution Of The Serotonin Transporter Linked Polymorphic Region (5-Httlpr) In Primates, Seth D. Dobson, Lauren J.N Brent Nov 2013

On The Evolution Of The Serotonin Transporter Linked Polymorphic Region (5-Httlpr) In Primates, Seth D. Dobson, Lauren J.N Brent

Dartmouth Scholarship

Some allelic variants of the serotonin transporter linked polymorphic region (5-HTTLPR) result in lower levels of expression of the serotonin transporter gene (SLC6A4). These low-expressing (LE) alleles are associated with mental-health disorders in a minority of humans that carry them. Humans are not the only primates that exhibit this polymorphism; other species, including some monkeys, also have LE and high-expressing (HE) variants of 5-HTTLPR. We propose a behavioral genetic framework to explain the adaptive evolution of this polymorphism in primates, including humans. We hypothesize that both LE and HE alleles are maintained by balancing selection in species characterized …

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Short Duration Waveforms Recorded Extracellularly From Freely Moving Rats Are Representative Of Axonal Activity, Ashlee A. Robbins, Steven E. Fox, Gregory L. Holmes, Rod C. Scott, Jeremy M. Barry Nov 2013

Short Duration Waveforms Recorded Extracellularly From Freely Moving Rats Are Representative Of Axonal Activity, Ashlee A. Robbins, Steven E. Fox, Gregory L. Holmes, Rod C. Scott, Jeremy M. Barry

Dartmouth Scholarship

While extracellular somatic action potentials from freely moving rats have been well characterized, axonal activity has not. We report direct extracellular tetrode recordings of putative axons whose principal feature is a short duration waveform (SDW) with an average peak-trough length less than 179 μs. While SDW recordings using tetrodes have previously been treated as questionable or classified as cells, we hypothesize that they are representative of axonal activity. These waveforms have significantly shorter duration than somatic action potentials, are triphasic and are therefore similar to classic descriptions of microelectrode recordings in white matter and of in vitro action potential propagation …

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Socially Excluded Individuals Fail To Recruit Medial Prefrontal Cortex For Negative Social Scenes, Katherine E. Powers, Dylan D. Wagner, Catherine J. Norris, Todd F. Heatherton Nov 2013

Socially Excluded Individuals Fail To Recruit Medial Prefrontal Cortex For Negative Social Scenes, Katherine E. Powers, Dylan D. Wagner, Catherine J. Norris, Todd F. Heatherton

Dartmouth Scholarship

Converging behavioral evidence suggests that people respond to experiences of social exclusion with both defensive and affiliative strategies, allowing them to avoid further distress while also encouraging re-establishment of positive social connections. However, there are unresolved questions regarding the cognitive mechanisms underlying people's responses to social exclusion. Here, we sought to gain insight into these behavioral tendencies by using functional magnetic resonance imaging (fMRI) to examine the impact of social exclusion on neural responses to visual scenes that varied on dimensions of sociality and emotional valence. Compared to socially included participants, socially excluded participants failed to recruit dorsomedial prefrontal cortex …

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Network Structure And Dynamics Of The Mental Workspace, Alexander Schlegel, Peter J. Kohler, Sergei V. Fogelson, Prescott Alexander Oct 2013

Network Structure And Dynamics Of The Mental Workspace, Alexander Schlegel, Peter J. Kohler, Sergei V. Fogelson, Prescott Alexander

Dartmouth Scholarship

The conscious manipulation of mental representations is central to many creative and uniquely human abilities. How does the human brain mediate such flexible mental operations? Here, multivariate pattern analysis of functional MRI data reveals a widespread neural network that performs specific mental manipulations on the contents of visual imagery. Evolving patterns of neural activity within this mental workspace track the sequence of informational transformations carried out by these manipulations. The network switches between distinct connectivity profiles as representations are maintained or manipulated.

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Understanding Less Than Nothing: Children's Neural Response To Negative Numbers Shifts Across Age And Accuracy, Margaret M. Gullick, George Wolford Sep 2013

Understanding Less Than Nothing: Children's Neural Response To Negative Numbers Shifts Across Age And Accuracy, Margaret M. Gullick, George Wolford

Dartmouth Scholarship

We examined the brain activity underlying the development of our understanding of negative numbers, which are amounts lacking direct physical counterparts. Children performed a paired comparison task with positive and negative numbers during an fMRI session. As previously shown in adults, both pre-instruction fifth-graders and post-instruction seventh-graders demonstrated typical behavioral and neural distance effects to negative numbers, where response times and parietal and frontal activity increased as comparison distance decreased. We then determined the factors impacting the distance effect in each age group. Behaviorally, the fifth-grader distance effect for negatives was significantly predicted only by positive comparison accuracy, indicating that …

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