Boston-NeuroTalks Calendar 3.0

John Assad (Harvard Neuroscience)

Abstract:

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 two180°-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.

http://www.hcs.harvard.edu/decision-ws/Spring_2012.html