Task-related activity in auditory cortex enhances sound representation
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In auditory-guided tasks, sound presentations often occupy a small fraction of the total task time. We studied here neuronal dynamics that spanned trial duration. Many neurons had large, slow, firing rate modulations, which were not driven by sounds, were larger than the sound evoked responses, and were locked to specific time points during the task, similar to responses of hippocampal time-sensitive neurons. Concurrently, responses to sounds differed between active behavior and passive listening conditions: in the active sessions, the on-going activity just before sound presentations was higher and the responses to target stimuli were weaker but more informative about the task-relevant sounds. We show that the slow firing rate modulations caused the increased on-going activity. Using a model, we demonstrate that higher on-going activity led to more synaptic depression of the cortico-cortical synapses, reducing the tendency to produce population spikes and resulting in weaker but more informative responses.
