Brown Bag Meetings

Winter Term

January 7

  • Speaker: Swaroop Gunthupalli, Graduate Student, Dartmouth College PBS
  • Title: In search of functional brain atlases: Deriving common categorical representational patterns across individuals.
  • Summary: Structural brain atlases that map common anatomical features play a seminal role in neuroscience. Similarly, functional brain atlases that map common functional activations corresponding to specific information across individuals can be of immense value. Such atlases built by anatomical registration across subjects only work for coarse-level category information such as houses and faces. To build a more generic functional brain atlas, we need to map common functional activation patterns corresponding to even fine-scale information. We present a new method, "hyperalignment" that transforms subject-specific representational patterns into common representational patterns. These transformed patterns of specific information are common across individuals and can be mapped back into the brain. This overcomes a major hurdle in building a functional brain atlas that can store universal brain activation pattern corresponding to particular content. Moreover, it is possible to derive a set of parameters for any individual's brain that can serve as a combination that unlocks the content represented by that subject's neural activity patterns using these functional atlases.

January 21

  • Speaker: Danny Dilks, Post-Doctoral Fellow, Kanwisher Lab
  • http://web.mit.edu/bcs/nklab/people.shtml
  • Title: Cortical reorganization in the human adult visual system
  • Summary: Many electrophysiological studies have reported plasticity (or “reorganization”) in primary visual cortex (V1) in adult animals: after lesioning the retina, the region of V1 deprived of bottom-up input begins torespond to stimuli that normally activate adjacent cortex only. However,the time course, underlying mechanisms, and even the very existence of thisreorganization are matters of intense controversy. Moreover, adult  cortical reorganization has not been well documented in the human visual system; nor have animal or human studies explored whether reorganization affects visualp erception. Here I report data from patients with deprived early visual cortex, and a consequent blind area (i.e., due to stroke and  culardegeneration). Behavioral and fMRI experiments provide a clear demonstration of cortical reorganization in the adult human visual system, and the first evidence that reorganization affects visual perception (e.g., a square presented adjacent to the blind area is perceived as a rectangle). To investigate the time course of such reorganization, I developed a novel perceptual paradigm to deprive a region of early visual cortex in people with ormal vision. I provide evidence that after only seconds of such deprivation distorted perception occurs (squares are perceived as rectangles). This result demonstrates that reorganization can occur very rapidly in adult retinotopic cortex, and implicates unmasking of pre-exisiting connections as the derlying mechanism. Taken together, these findings contribute to our understanding of the human adult brain’s capacity to change, and have implications for fundamental topics such as development, learning, and recovery from brain damage.

February 4

  • Speaker: Dongqing Shi, Post-Doctoral Fellow, Kralik Lab, PBS
  • Title: A Biologically Inspired Solution for Partially Observable Stochastic Games with Different Payoffs
  • Summary: The research examines how each agent in a decentralized team makes decisions when it is subject to environmental and teammate uncertainties, where the interacting environment is only partially observable and the teammate decisions are not known. The problem is modeled as a partially observable stochastic game (POSG). To encourage cooperation among players, POSGs are mostly considered to have common payoffs; however, this is not always true for many practical problems. We present a biologically inspired method for solving general different payoff POSGs. The biologically inspired grouping method first separates the original complex POSG into smaller identical POSGs, and each smaller POSG is solved as a series of Bayesian games, thus avoiding the more difficult and frequently intractable problem of solving complex POSGs from the outset. We present an approximate solution for the POSG game with different payoffs by introducing a new heuristic Q_{MAMDP}, the Q values of the corresponding fully observable, multi-agent Markov decision process. The simulation results have shown both cooperative and competitive behaviors of the multi-agent team.

February 18

  • Speaker: Dave Bucci, Ph.D., Associate Professor, Dartmouth College PBS
  • Title: Cortico-Hippocampal Circuits: Unique Contributions to Learning and Memory

March 4

  • Speaker: Dan Graham, Post-Doctoral Fellow, Meng Lab, PBS
  • http://math.dartmouth.edu/~dgraham/
  • Title: The Packet-Switching Brain: A Hypothesis
  • Summary: Despite great advances in our understanding of neural responses to natural stimuli, the basic structure of the neural code remains elusive. In this talk, I will describe a novel hypothesis regarding the fundamental structure of neural coding in mammals. In particular, I propose that an internet-like routing architecture (specifically packet-switching) underlies neocortical processing, and I propose means of testing this hypothesis via neural response sparseness measurements. I will synthesize a host of suggestive evidence that supports this notion and will, more generally, argue in favor of a large scale shift from the now dominant “computer metaphor,” to the “internet metaphor.” This shift is intended to spur new thinking with regard to neural coding, and its main contribution is to privilege communication over computation as the prime goal of neural systems.

April 1

  • Speaker: Dave Bucci, Associate Professor, Dartmouth College PBS
  • http://www.dartmouth.edu/~buccilab/
  • Title: Cortico-Hippocampal Circuits: Unique Contributions to Learning and Memory

April 15

  • CNS Practice Poster Session
  • Presenters:
  • Margaret Gullick, Swaroop Gunthapalli, Yune Lee, Carolyn Parkinson, Lisa Sprute

April 29

  • Speaker: Brian Russ, Post-doctoral Fellow, Hauser Lab
  • Title: 
  • Title: Cues to competition recognition in free-ranging rhesus monkeys, Macaca mulatta.
  • Summary: All socially living animals are confronted with the challenge of competing over limited resources. When resources are moveable a relatively open empirical question concerns how potential competitors recognize that another individual has a claim on a resource and when such claims should be respected. Here we address these features of competition in free-ranging rhesus monkeys by using a competitive foraging task involving two food options. In two sets of experiments we manipulated different aspects of the competitors' potential competitive advantage to test how rhesus interacted with the competitors. In the first set of conditions, we focused on aspects of the competitor’s physical connection to the food, his attentional state, and proximity. Results of this first experiment reveal that rhesus monkeys use a variety of cues focusing on attention and physical connectivity when recognizing and respecting competitive advantages. Next in the second set of conditions, we systematically explored how the monkeys use food possession to identify the more vigorous of two human competitors. Results showed that in the absence of any training, rhesus preferentially avoided the last individual to contact the food.

May 13

  • Speaker: TBA

May 27

  • Speaker: TBA