SENSORY INTEGRATION AND WORKING MEMORY

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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. We proposed experiments that test hypotheses about the neural mechanisms that underlie the brain's ability to make decisions. Our experiments address the mechanism used by the brain to convert sensory information represented by neurons in the visual cortex to a decision about what this information means for purposes of planning behavior. 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 that the neurons we have been studying in the parietal lobe play a causal role in the decision process (Hanks et al, 2006). We also discovered that these neurons perform a type of arithmetic that ressembles the addition and subtraction of lograrithms of probabilities  the very mathematical operation that a statistician would perform on a stream of data in order to make a decision (Yang and Shadlen, 2007). We have also extended our understanding of the mechanism to decisions under different time pressures and among more than 2 options (Kiani et al, in review at J. Neurosci; Churchland et al, in review at Nat Neurosci). Several theoretical papers and an important review paper were published this year (Gold and Shadlen, 2007; Shadlen et al, in press; Wong et al, 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.