ANNULÉ - Scalable neural population dynamics underlying cognition in the basal ganglia

Time, like space, is a fundamental dimension of animals’ worlds. To  behave adaptively, organisms must extract temporal structure from  experience and construct temporally patterned  behavior. Yet, the  mechanisms for doing so are poorly understood. The striatum, a main input structure of the basal ganglia, has been implicated in several  time-dependent functions such as reinforcement learning and action  selection. To determine the mechanisms underlying temporal processing in these circuits, we manipulated and recorded the activity of dorsal striatal neurons in rats performing a duration categorization task. We found that faster or slower population dynamics predicted longer or shorter duration judgments and that simultaneously recorded neuronal ensembles could judge duration as well as the animal. Additionally, pharmacological perturbation of striatal tissue produced a marked decrease in timing accuracy. To directly assess whether variability in the speed of striatal population dynamics causes variability in duration judgments, we manipulated temperature, a method capable of affecting dynamics but not patterning of neural responses. We recorded from striatal populations under different temperatures in anesthetized animals using high density silicon probes (neuropixels) combined with a 
custom-made solid-state thermoelectric implant. Reproducible striatal dynamics were elicited by optogenetic stimulation of the ventral posterior lateral thalamus, and higher or lower temperaturesproduced a relative speeding or slowing of these dynamics. When striatal 
temperature was manipulated during task performance, cooling or warming striatal tissue caused graded underestimation or overestimation of duration, respectively, but left timing of motor execution unaffected. These data demonstrate that the speed with which neural populations 
traverse a trajectory in neural space reflects the evolution of a cognitive decision variable,dissociable from motor function, that is used to guide judgments of duration. Lastly, cell-type specific calcium imaging and optogenetic inhibition in mice revealed a likely functional identity of the dominant decision-variable carried by striatal circuits during the task: the time varying need to suppress execution of particular choices. More generally, these data provide a basis for thinking about how the basal ganglia generate signals that are functions of elapsed time for the purposes of learning and behavioral control.