Decision-making is an important cognitive ability that often requires uncertain evidence to be weighed and accumulated over time before committing to a course of action. Much of our understanding of the neural mechanisms responsible for this process of evidence accumulation comes from neurophysiological studies in monkeys performing demanding perceptual decision- making tasks. In one particularly well-studied model, monkeys are trained to decide the direction of motion of a noisy visual stimulus and indicate their decision with an eye movement to a target located in the perceived direction of motion. These studies suggest that neurons in the lateral intraparietal area (LIP) of parietal cortex play a role in accumulating noisy motion evidence used to instruct the oculomotor response. However, in this task the close relationship between formation of the direction decision and selection of the appropriate oculomotor response makes it difficult to identify the exact role of LIP. In particular, does LIP encode the decision about motion direction independent of the motor act, or does it reflect an oculomotor selection process that can access relevant perceptual information? Our central hypothesis is that LIP encodes an oculomotor selection process. To test this hypothesis we will train monkeys using an innovative task design in which their decision about the direction of motion is associated with the color, instead of the location, of the choice target (red for rightward motion, green for leftward). For a given session the locations of the two targets are fixed, but we randomly assign to them the two colors. Critically, we manipulate the time when the colors are assigned and measure the effects on the representation of evidence accumulation in LIP. When the color assignment occurs before motion viewing, the direction decision can be used directly to select the appropriate oculomotor response and LIP is likely to be engaged. When the color assignment occurs after motion viewing, the specific oculomotor response is not known while the decision is formed and LIP might not be engaged. When the color assignment occurs during motion viewing, LIP neurons might be able to gain dynamic access to a process of evidence accumulation that is being carried out elsewhere in the brain. The results will clarify the role of LIP in perceptual decision-making and provide a more general understanding of the principles that govern how behavioral context can influence how and where in the brain high-order abilities like decision-making are generated.
The proposed work is basic research, designed to provide new insights into how a healthy nervous system evaluates evidence to form a decision. Thus, direct benefits to public health are expected to come in the longer term, as these new insights can be used to design new ways to diagnose and treat disorders that affect perception and judgment.
|Fitzgerald, Jamie K; Freedman, David J; Fanini, Alessandra et al. (2013) Biased associative representations in parietal cortex. Neuron 77:180-91|
|Bennur, Sharath; Gold, Joshua I (2011) Distinct representations of a perceptual decision and the associated oculomotor plan in the monkey lateral intraparietal area. J Neurosci 31:913-21|