State-dependent intracortical connectivity in the mouse visual cortex

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Thalamocortical circuits process sensory input during waking, and spontaneously generate synchronized activity characteristic of sleep. Activity-dependent plasticity shapes thalamocortical pathway during development, however what types of activity are required remains unknown. Here we report altered visual processing during sleep, enhancement of neuronal connectivity, and its regulation by inhibition, using multiple-single unit recording across sleep-wake cycles in the visual cortex of behaving mice. Visual response during slow-wave sleep (SWS) was distinct from that of waking. Enhancement of functional connectivity among neurons during SWS was revealed by cross-correlation analysis. Moreover, the enhancement was significant even in putative monosynaptic intracortical connections. In GABA-synthetic enzyme knockout mice which retain a latent cortical plasticity, the monosynaptic enhancement by sleep was severely impaired, and reversibly restored by facilitation of inhibitory transmission using diazepam. Our results suggest functional connectivity in SWS is controlled by inhibitory system and is involved in expression of cortical plasticity.