Membrane potential correlates of network decorrelation and improved SNR by cholinergic activation in the somatosensory cortex.

The nucleus basalis (NB) projects cholinergic axons to the cortex where they play a major role in arousal, attention and learning. Cholinergic inputs shift cortical dynamics from synchronous to asynchronous and improves the signal to noise ratio (SNR) of sensory response. Yet, the underlying mechanisms of these changes remain unclear. Using simultaneous extracellular and whole cell patch recordings in layer 4 barrel cortex we show that activation of the cholinergic system has a differential effect on ongoing and sensory evoked activities. Cholinergic activation eliminated the large and correlated spontaneous synaptic fluctuations in membrane potential while sparing the synaptic response to whisker stimulation. This differential effect of cholinergic activation provides a unified explanation for the increased SNR of sensory response and for the reduction in both trial to trial variability and noise correlations as well as explaining the shift into desynchronized cortical state which are the hallmarks of arousal and attention.