**Faculty Candidate - Systems Neuroscience**
The cortex represents information across widely varying timescales. For instance, sensory cortex encodes stimuli that fluctuate over milliseconds, whereas in association cortex behavioral choices can require the maintenance of information over seconds. It is poorly understood how the cortex achieves such diverse timescales of information coding. While recent work has identified different timescales in features intrinsic to individual neurons, the timescales of information coding in populations of neurons have not been studied, and population codes have not been compared in depth across cortical regions. I will discuss our recent findings that population codes are essential to achieve long and diverse coding timescales, and that codes differ fundamentally between sensory and association cortices. We compared coding for sensory stimuli and behavioral choices in auditory cortex (AC) and posterior parietal cortex (PPC) as mice performed a sound localization task. Information about the auditory stimulus was present in AC but not PPC, whereas both regions contained information about the mouse’s choice. Although both regions coded information by tiling in time neurons that were transiently informative for less than ~200 milliseconds, the areas had major differences in functional coupling between neurons, measured as activity correlations that could not be explained by task events. Coupling among PPC neurons was strong, extended over long time lags, and contributed to a long timescale population code characterized by consistent representations of choice lasting over two seconds. In contrast, coupling among AC neurons was weak, shorter-lived, and resulted in moment-to-moment fluctuations in stimulus and choice information. Our results suggest that population coupling is a variable property that affects the timescale of information coding: relatively uncoupled activity in sensory cortex is key for signals that change rapidly to code temporally variable stimuli, whereas highly coupled activity in association cortex appears critical to form a consistent signal from which temporally integrated information can be read out instantaneously to drive behavior. Finally, I will discuss plans for my future work, to study communication between cortical networks, and the circuit mechanisms underlying its modulation by behavioral context and brain state.