Task-related activity in auditory cortex enhances sound representation

We describe here a mode of activity of neurons in auditory cortex of freely moving rats consisting of 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. This activity mode had important functional consequences to sound processing during task performance. We show that the slow firing rate modulations caused the ongoing activity just before sound presentations to be higher during task performance than during passive listening. Concurrently, during task performance, the responses to target stimuli were weaker but more informative about the task-relevant sounds. In a model, higher ongoing activity caused more synaptic depression of the cortico-cortical synapses, reducing the tendency of the network to produce population spikes and resulting in weaker but more informative responses to sounds.