Scaling down of balanced excitation and inhibition by active behavioral states in auditory cortex.

Cortical sensory processing is modulated by behavioral and cognitive states. How this modulation is achieved by changing synaptic circuits remains largely unknown. In awake mouse auditory cortex, we found that sensory-evoked spike responses of layer 2/3 (L2/3) excitatory cells were scaled down with preserved sensory tuning when mice transitioned from quiescence to active behaviors, including locomotion, whereas L4 and thalamic responses were unchanged. Whole-cell voltage-clamp recordings revealed that tone-evoked synaptic excitation and inhibition exhibited a robust functional balance. The change to active states caused scaling down of excitation and inhibition at approximately equal levels in L2/3 cells, but resulted in no synaptic changes in L4 cells. This lamina-specific gain control could be attributed to an enhancement of L1-mediated inhibitory tone, with L2/3 parvalbumin inhibitory neurons also being suppressed. Thus, L2/3 circuits can adjust the salience of output in accordance with momentary behavioral demands while maintaining the sensitivity and quality of sensory processing.