Inhibition dominates sensory responses in the awake cortex (original) (raw)

The activity of the cerebral cortex is thought to depend on the precise relationship between synaptic excitation and inhibition 1-4 . In visual cortex, in particular, intracellular measurements have related response selectivity to coordinated increases in excitation and inhibition 5-9 . These measurements, however, have all been performed during anaesthesia, which strongly influences cortical state 10 and therefore sensory processing 7,11-15 . The synaptic activity evoked by visual stimulation during wakefulness is unknown. Here, we measured visually evoked responses -and the underlying synaptic conductances -in the visual cortex of anaesthetised and awake mice. Under anaesthesia, responses could be elicited from a large region of visual space 16 and were prolonged in time. During wakefulness responses were more spatially selective and much briefer. Whole-cell patch-clamp recordings of synaptic conductances 5,17 revealed a surprising difference in synaptic inhibition during the two conditions. Whereas under anaesthesia inhibition tracked excitation in amplitude and spatial selectivity, during wakefulness it was much stronger than excitation and exhibited extremely broad spatial selectivity. We conclude that during wakefulness cortical responses to visual stimulation are dominated by synaptic inhibition, restricting their spatial spread and temporal persistence. These results provide the first direct glimpse of synaptic mechanisms that control visual responses in the awake cortex.