grad

_pages/about.md

@@ -8,8 +8,7 @@ redirect_from:
   - /about.html
 ---
 
+I am currently a researcher in Neuromorphic and Cognitive Computing at [Sandia National Labs](https://neuroscience.sandia.gov). My work here involves creating abstractions of architectures, dynamics, and learning rules from neuroscience findings. I then translate these abstractions into practical applications for next-generation machine intelligence, particularly on novel brain-inspired hardware.
 
-I'm currently a PhD student in Computational & Cognitive Neuroscience at Boston University, working with [Michael Hasselmo](http://bu.edu/hasselmo). My research focuses on creating computational models of neocortex to investigate how cortical architecture can enable self-supervised learning by predictive coding.
-
-Before starting my PhD I worked with [Randy O'Reilly](https://psychology.ucdavis.edu/people/oreilly) during my master's program at University of Colorado Boulder. My undergraduate education was in biomedical engineering. 
-
+I completed my PhD in Computational & Cognitive Neuroscience at Boston University, working with [Michael Hasselmo](http://bu.edu/hasselmo), where I investigated models of neocortical microcircuits that enabled self-supervised learning by predictive coding. 
+Before starting my PhD I worked with [Randy O'Reilly](https://psychology.ucdavis.edu/people/oreilly) during my master's program at University of Colorado Boulder, investigating neural mechanisms of attention. My undergraduate education was in biomedical engineering, where I developed microelectronics for lab-on-a-chip applications and created predictive models for [Alzheimer's Disease detection](https://www.vumc.org/vmac).

_pages/cv.md

@@ -13,15 +13,16 @@ Also available in a printable format <a href="https://wchapman.github.io/files/r
 
 Education
 ======
-* Ph.D Boston University, Computational Neuroscience, April 2023 (expected)
+* Ph.D Boston University, Computational Neuroscience, May 2023
 * M.S. University of Colorado Boulder, Cognitive Neuroscience, 2018
   * Thesis: "A Model of Relational Reasoning Through Selective Attention". [PDF](https://www.researchgate.net/publication/328289450_A_Model_of_Relational_Reasoning_Through_Selective_Attention)
 * B.S. Boston University, Biomedical Engineering, 2012
 
 
 Work experience
 ======
-* Graduate Research Fellow, *Boston University*, 2018 - Present
+* Postdoctoral Appointee, Neuromorphic Computing, *Sandia National Labs*, 2023 - Present
+* Graduate Research Fellow, *Boston University*, 2018 - 2023
   * **Biological Predictive Coding**: Created a novel, biologically inspired, machine learning architecture and learning rule
 for temporal prediction. Functions above state-of-the-art for both short-term and long-term sequence generation, with
 applications for lifelong learning, and generalization

_publications/alexander_hasselmo_2019.md

@@ -4,6 +4,6 @@ collection: publications
 Venue: NA 
 abstract: 'Abstract The retrosplenial cortex is reciprocally connected with a majority of structures implicated in spatial cognition and damage to the region itself produces numerous spatial impairments However in many ways the retrosplenial cortex remains understudied Here we sought to characterize spatial correlates of neurons within the region during free exploration in twodimensional environments We report that a large percentage of retrosplenial cortex neurons have spatial receptive fields that are active when environmental boundaries are positioned at a specific orientation and distance relative to the animal itself We demonstrate that this vectorbased location signal is encoded in egocentric coordinates localized to the dysgranular retrosplenial subregion independent of selfmotion and context invariant Further we identify a subpopulation of neurons with this response property that are synchronized with the hippocampal theta oscillation Accordingly the current work identifies a robust egocentric spatial code in retrosplenial cortex that can facilitate spatial coordinate system transformations and support the anchoring generation and utilization of allocentric representations'
 date: 2019-7-1
-paperurl: /files/myPubs/files/2581/alexander_hasselmo_2019.pdf
+paperurl: /files/myPubs/files/3676/alexander_hasselmo_2019.pdf
 citation: 'A.S. Alexander, L.C. Carstensen, J.R. Hinman, F. Raudies, G.W. Chapman, M.E. Hasselmo. "Egocentric Boundary Vector Tuning Of The Retrosplenial Cortex", <i>Science Advances</i>, 2019.'
 ---

_publications/alexander_hasselmo_2020.md

@@ -4,6 +4,6 @@ collection: publications
 Venue: NA 
 abstract: 'Neurophysiological recordings in behaving rodents demonstrate neuronal response properties that may code space and time for episodic memory and goaldirected behaviour Here we review recordings from hippocampus entorhinal cortex and retrosplenial cortex to address the problem of how neurons encode multiple overlapping spatiotemporal trajectories and disambiguate these for accurate memoryguided behaviour The solution could involve neurons in the entorhinal cortex and hippocampus that show mixed selectivity coding both time and location Some grid cells and place cells that code space also respond selectively as time cells allowing differentiation of time intervals when a rat runs in the same location during a delay period Cells in these regions also develop new representations that differentially code the context of prior or future behaviour allowing disambiguation of overlapping trajectories Spiking activity is also modulated by running speed and head direction supporting the coding of episodic memory not as a series of snapshots but as a trajectory that can also be distinguished on the basis of speed and direction Recent data also address the mechanisms by which sensory input could distinguish different spatial locations Changes in firing rate reflect running speed on long but not short time intervals and few cells code movement direction arguing against path integration for coding location Instead new evidence for neural coding of environmental boundaries in egocentric coordinates fits with a modelling framework in which egocentric coding of barriers combined with head direction generates distinct allocentric coding of location The egocentric input can be used both for coding the location of spatiotemporal trajectories and for retrieving specific viewpoints of the environment Overall these different patterns of neural activity can be used for encoding and disambiguation of prior episodic spatiotemporal trajectories or for planning of future goaldirected spatiotemporal trajectories'
 date: 2020-1-1
-paperurl: /files/myPubs/files/3787/alexander_hasselmo_2020.pdf
+paperurl: /files/myPubs/files/4083/alexander_hasselmo_2020.pdf
 citation: 'A.S. Alexander, J.C. Robinson, H. Dannenberg, N.R. Kinsky, S.J. Levy, W. Mau, G.W. Chapman, D.W. Sullivan, M.E. Hasselmo. "Neurophysiological Coding Of Space And Time In The Hippocampus Entorhinal Cortex And Retrosplenial Cortex", <i>Brain and Neuroscience Advances</i>, 2020.'
 ---

_publications/alexander_nitz_2022.md

@@ -2,8 +2,8 @@
 title: 'Adaptive Integration Of Selfmotion And Goals In Posterior Parietal Cortex'
 collection: publications
 Venue: NA 
-abstract: 'Rats readily switch between foraging and more complex navigational behaviors such as pursuit of other rats or prey These tasks require vastly different tracking of multiple behaviorally signicant variables including selfmotion state To explore whether navigational context modulates selfmotion tracking we examined selfmotion tuning in posterior parietal cortex neurons during foraging versus visual target pursuit Animals performing the pursuit task demonstrate predictive processing of target trajectories by anticipating and intercepting them Relative to foraging pursuit yields multiplicative gain modulation of selfmotion tuning and enhances selfmotion state decoding Selfmotion sensitivity in parietal cortex neurons is on average history dependent regardless of behavioral context but the temporal window of selfmotion integration extends during target pursuit Finally many selfmotionsensitive neurons conjunctively track the visual target position relative to the animal Thus posterior parietal cortex functions to integrate the location of navigationally relevant target stimuli into an ongoing representation of past present and future locomotor trajectories'
+abstract: 'Rats readily switch between foraging and more complex navigational behaviors such as pursuit of other rats or prey These tasks require vastly different tracking of multiple behaviorally significant variables including selfmotion state To explore whether navigational context modulates selfmotion tracking we examined selfmotion tuning in posterior parietal cortex neurons during foraging versus visual target pursuit Animals performing the pursuit task demonstrate predictive processing of target trajectories by anticipating and intercepting them Relative to foraging pursuit yields multiplicative gain modulation of selfmotion tuning and enhances selfmotion state decoding Selfmotion sensitivity in parietal cortex neurons is on average history dependent regardless of behavioral context but the temporal window of selfmotion integration extends during target pursuit Finally many selfmotionsensitive neurons conjunctively track the visual target position relative to the animal Thus posterior parietal cortex functions to integrate the location of navigationally relevant target stimuli into an ongoing representation of past present and future locomotor trajectories'
 date: 2022-3-1
-paperurl: /files/myPubs/files/4580/1-s2.0-S2589004221013481-main.pdf
+paperurl: /files/myPubs/files/4749/alexander_nitz_2022.pdf
 citation: 'A.S. Alexander, J.C. Tung, G.W. Chapman, A.M. Conner, L.E. Shelley, M.E. Hasselmo, D.A. Nitz. "Adaptive Integration Of Selfmotion And Goals In Posterior Parietal Cortex", <i>Cell Reports</i>, 2022.'
 ---

_publications/carstensen_hasselmo_2022.md

@@ -2,8 +2,8 @@
 title: 'Neural Responses In Retrosplenial Cortex Associated With Environmental Alterations'
 collection: publications
 Venue: NA 
-abstract: 'The retrosplenial cortex RSC is an area interconnected with regions of the brain that display spatial correlates Neurons in connected regions may encode an animals position in the environment and location or proximity to objects or boundaries RSC has also been shown to be important for spatial memory such as tracking distance from and between landmarks contextual information and orientation within an environment For these reasons it is important to determine how neurons in RSC represent cues such as objects or boundaries and their relationship to the environment In the current work we performed electrophysiological recordings in RSC whereas rats foraged in arenas that could contain an object or in which the environment was altered We report RSC neurons display changes in mean ring rate responding to alterations of the environment These alterations include the arena rotating changing size or shape or an object being introduced into the arena'
+abstract: 'The retrosplenial cortex RSC is an area interconnected with regions of the brain that display spatial correlates Neurons in connected regions may encode an animals position in the environment and location or proximity to objects or boundaries RSC has also been shown to be important for spatial memory such as tracking distance from and between landmarks contextual information and orientation within an environment For these reasons it is important to determine how neurons in RSC represent cues such as objects or boundaries and their relationship to the environment In the current work we performed electrophysiological recordings in RSC whereas rats foraged in arenas that could contain an object or in which the environment was altered We report RSC neurons display changes in mean firing rate responding to alterations of the environment These alterations include the arena rotating changing size or shape or an object being introduced into the arena'
 date: 2021-11-1
-paperurl: /files/myPubs/files/4581/Carstensen et al. - 2021 - Neural responses in retrosplenial cortex associate.pdf
+paperurl: /files/myPubs/files/4746/carstensen_hasselmo_2022.pdf
 citation: 'L.C. Carstensen, A.S. Alexander, G.W. Chapman, A.J. Lee, M.E. Hasselmo. "Neural Responses In Retrosplenial Cortex Associated With Environmental Alterations", <i>iScience</i>, 2021.'
 ---

_publications/chapman_hasselmo_2023.md

@@ -0,0 +1,9 @@
+---
+title: 'Predictive Learning By A Burstdependent Learning Rule'
+collection: publications
+Venue: NA 
+abstract: 'Humans and other animals are able to quickly generalize latent dynamics of spatiotemporal sequences often from a minimal number of previous experiences Additionally internal representations of external stimuli must remain stable even in the presence of sensory noise in order to be useful for informing behavior In contrast typical machine learning approaches require many thousands of samples and generalize poorly to unexperienced examples or fail completely to predict at long timescales Here we propose a novel neural network module which incorporates hierarchy and recurrent feedback terms constituting a simplified model of neocortical microcircuits This microcircuit predicts spatiotemporal trajectories at the input layer using a temporal error minimization algorithm We show that this module is able to predict with higher accuracy into the future compared to traditional models Investigating this model we find that successive predictive models learn representations which are increasingly removed from the raw sensory space namely as successive temporal derivatives of the positional information Next we introduce a spiking neural network model which implements the ratemodel through the use of a recently proposed biological learning rule utilizing dualcompartment neurons We show that this network performs well on the same tasks as the meanfield models by developing intrinsic dynamics that follow the dynamics of the external stimulus while coordinating transmission of higherorder dynamics Taken as a whole these findings suggest that hierarchical temporal abstraction of sequences rather than feedforward reconstruction may be responsible for the ability of neural systems to quickly adapt to novel situations'
+date: 2023-1-1
+paperurl: /files/myPubs/files/7177/chapman_hasselmo_2023.pdf
+citation: 'G.W. Chapman, M.E. Hasselmo. "Predictive Learning By A Burstdependent Learning Rule", <i>Neurobiology of Learning and Memory</i>, 2023.'
+---

_publications/ferrante_hasselmo_2016.md

@@ -4,6 +4,6 @@ collection: publications
 Venue: NA 
 abstract: 'Abstract Medial Entorhinal Cortex LayerII stellate cells mECLIISCs primarily interact via inhibitory interneurons This suggests the presence of alternative mechanisms other than excitatory synaptic inputs for triggering action potentials APs in stellate cells during spatial navigation Our intracellular recordings show that the hyperpolarizationactivated cation current Ih allows Post InhibitoryReboundSpikes PIRS in mECLIISCs Invivo strong InhibitoryPostSynaptic Potentials IPSPs immediately preceded most APs shortening their delay and enhancing excitability Invitro experiments showed that inhibition initiated spikes more effectively than excitation and that more dorsal mECLIISCs produced faster and more synchronous spikes In contrast PIRS in LayerII/III pyramidal cells PCs were harder to evoke voltageindependent and slower in dorsal mEC In computational simulations mECLIISCs morphology and Ih homeostatically regulated the dorsoventral DV differences in PIRS timing and most dendrites generated PIRS with a narrow range of stimulus amplitudes These results suggest inhibitory inputs could mediate the emergence of grid cell firing in a neuronal network'
 date: 2016-1-1
-paperurl: /files/myPubs/files/2587/ferrante_hasselmo_2016.pdf
+paperurl: /files/myPubs/files/3682/ferrante_hasselmo_2016.pdf
 citation: 'M. Ferrante, C.F. Shay, Y. Tsuno, G.W. Chapman, M.E. Hasselmo. "Postinhibitory Rebound Spikes In Rat Medial Entorhinal Layer Ii/Iii Principal Cells Invivo Invitro And Computational Modeling Characterization", <i>Cerebral Cortex</i>, 2016.'
 ---

_publications/gifford_jefferson_2015.md

@@ -2,8 +2,8 @@
 title: 'Subjective Memory Complaint Only Relates To Verbal Episodic Memory Performance In Mild Cognitive Impairment'
 collection: publications
 Venue: NA 
-abstract: 'Objective A cognitive concern from the patient informant or clinician is required for the diagnosis of mild cognitive impairment MCI however the cognitive and neuroanatomical correlates of complaint are poorly understood We assessed how selfcomplaint relates to cognitive and neuroimaging measures in older adults with MCI Method MCI participants were drawn from the Alzheimers Disease Neuroimaging Initiative and dichotomized into two groups based on the presence of selfreported memory complaint no complaint n191 777 years complaint n206 738 years Cognitive outcomes included episodic memory executive functioning information processing speed and language Imaging outcomes included regional lobar volumes frontal parietal temporal cingulate and specific medial temporal lobe structures hippocampal volume entorhinal cortex thickness parahippocampal gyrus thickness Results Linear regressions adjusting for age sex race education MiniMental State Examination mood and apolipoprotein E4 status found that cognitive complaint related to immediate 107 ptextless0001 and delayed episodic memory performances assessed on a serial list learning task 106 p0001 but no other cognitive measures or neuroimaging markers Conclusions Selfreported memory concern was unrelated to structural neuroimaging markers of atrophy and measures of information processing speed executive functioning or language In contrast memory selfcomplaint related to objective verbal episodic learning performance Future research is warranted to better understand the relation between cognitive complaint and surrogate markers of abnormal brain aging including Alzheimers disease across the cognitive aging spectrum'
+abstract: 'Objective A cognitive concern from the patient informant or clinician is required for the diagnosis of mild cognitive impairment MCI however the cognitive and neuroanatomical correlates of complaint are poorly understood We assessed how selfcomplaint relates to cognitive and neuroimaging measures in older adults with MCI Method MCI participants were drawn from the Alzheimers Disease Neuroimaging Initiative and dichotomized into two groups based on the presence of selfreported memory complaint no complaint n191 77pm7 years complaint n206 73pm8 years Cognitive outcomes included episodic memory executive functioning information processing speed and language Imaging outcomes included regional lobar volumes frontal parietal temporal cingulate and specific medial temporal lobe structures hippocampal volume entorhinal cortex thickness parahippocampal gyrus thickness Results Linear regressions adjusting for age sex race education MiniMental State Examination mood and apolipoprotein E4 status found that cognitive complaint related to immediate beta107 p0001 and delayed episodic memory performances assessed on a serial list learning task beta106 p0001 but no other cognitive measures or neuroimaging markers Conclusions Selfreported memory concern was unrelated to structural neuroimaging markers of atrophy and measures of information processing speed executive functioning or language In contrast memory selfcomplaint related to objective verbal episodic learning performance Future research is warranted to better understand the relation between cognitive complaint and surrogate markers of abnormal brain aging including Alzheimers disease across the cognitive aging spectrum'
 date: 2015-1-1
-paperurl: /files/myPubs/files/2589/gifford_jefferson_2015.pdf
-citation: 'K.a. Gifford, D. Liu, S.M. Damon, G.W. Chapman, R.R. Romano, L.R. Samuels, Z. Lu, A.L. Jefferson. "Subjective Memory Complaint Only Relates To Verbal Episodic Memory Performance In Mild Cognitive Impairment", <i>Journal of Alzheimers Disease</i>, 2015.'
+paperurl: /files/myPubs/files/3684/gifford_jefferson_2015.pdf
+citation: 'K. Gifford, D. Liu, S.M. Damon, G.W. Chapman, R.R. Romano, L.R. Samuels, Z. Lu, A.L. Jefferson. "Subjective Memory Complaint Only Relates To Verbal Episodic Memory Performance In Mild Cognitive Impairment", <i>Journal of Alzheimers Disease</i>, 2015.'
 ---