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John Assad

John Assad, Department of Neurobiology, Harvard Medical School, and Center for Neuroscience and Cognitive Systems, Italian Institute of Technology

Wednesday 3th July 2013

Time: 4pm

 

Basement Seminar Room

Alexandra House, 17 Queen Square, London, WC1N 3AR

 

"ASSOCIATIONS AND DECISIONS IN PARIETAL CORTEX."

The inferior parietal lobe is involved in the perception of visual space and the control of eye movements. Neurons in the primate lateral intraparietal area (LIP) have also been implicated in perceptual decision-making. In those experiments, monkeys typically signal their percept by making saccadic eye movements in specific directions. We asked whether parietal neurons are involved in decisions that do not have a spatially specific motor read-out. In our first experiment, we trained monkeys to group directions of motion into two 180°-wide “categories”. After training, we found that LIP neurons reflected the learned category boundary, in that individual neurons tended to respond similarly within direction categories but differently between categories. We examined the generality of these effects by training animals in a paired-associate task in which the animals learned to group pairs of arbitrarily chosen static shapes. We found again that LIP neurons reflected the learned pair-associations, in that individual neurons tended to respond more similarly for associated pairs of shapes than for unassociated pairs of shapes. In both the direction-categorization task and the shape-paired-associate task we used a delayed match-to-category (-pair) paradigm that dissociated the category (pair) identity from the hand movement the animal used to signal its report. We also controlled carefully for behavioral artifacts that could have produced the observed neuronal selectivity. Our results suggest that parietal neurons provide decisional signals that do not fit in a spatial- or motor-based framework. These findings challenge the generality of models positing that categorical decisions are represented in an action- or intention-based framework. Action-based frameworks have been proposed for other brain representations, such as for the representation of value. However, we also find action-independent neuronal representations of value in orbitofrontal cortex. We hypothesize that non-action-based representations are prevalent in the brain and can be revealed by appropriate experimental design.

 

Biography

John Assad received his PhD in Neurobiology at Harvard Medical School, working on cellular biophysics, and did a postdoc in systems neuroscience with John Maunsell at Baylor College of Medicine. He has been on the faculty of Harvard Medical School since 1996, where he is currently Full Professor of Neurobiology, and he is also currently an acting director of neuroscience at the Italian Institute of Technology in Genova, Italy. His recent work has focused on higher-order sensorimotor control and economic decision-making in the non-human primate brain.