SENSORY INTEGRATION AND WORKING MEMORY

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Our experiments test hypotheses about the neural mechanisms that underlie the brain's ability to make decisions. They build on knowledge of how the brain represents information about the movement of objects in vision. Our experiments expose the conversion of sensory evidence in visual cortex to a decision about the direction of motion. We showed that neurons in the association cortex of the macaque represent the accumulation of this evidence for one choice and against an alternative. This year, we demonstrated, using cortical microstimulation, that the activity of neurons in the lateral intraparietal area (LIP) play a causal role in this decision process (Hanks et al, 2006). We have also extended our experimental work in several important ways. We demonstrated that the parietal cortex adds and subtracts quantities that approximate the logarithm of probabilities, thus lending insight into the very basis of rational thought (Yang and Shadlen, under review). We discovered a mechanism through which bias and sensory evidence are combined in decision making (Shadlen et al, 2006), and we have nearly completed data collection on a second monkey in a project that extends the study of binary decisions (e.g., left or right) to more than two choices (e.g., left, right, up or down)(Churchland et al., 2006). Further, we have recently discovered that the neural mechanism that governs the tradeoff between decision speed and accuracy also explains the limits in perceptual accuracy that are commonly observed when a decision maker is given a set amount of information (Kiani et al., 2006). Finally, we have developed a theoretical framework for understanding decision making, which is summarized in two articles (Shadlen et al., 2006; Gold and Shadlen, 2007). Decision-making bridges the gap between sensation and behavior. Nearly all non-reflexive behaviors require the brain to draw upon its sensory cortex to guide future behavior. Thus, the neural mechanisms for the simple decisions we study are likely to lend insight into more complex cognitive strategies. Our experiments ultimately furnish new insights into the causes and treatments of mental disorders affecting perception, planning and reasoning.