Rare cortical inhibitory neurons drive widespread synchrony and promote sleep

The researchers combined sparse labeling, whole-brain reconstruction, and monosynaptic rabies tracing to map the dense local and extensive ipsilateral projections of Sst-Chodl neurons, a GABAergic subtype comprising less than 1 % of cortical inhibitory cells. In vivo two-photon calcium imaging revealed that these cells are selectively active during low-arousal, synchronized cortical states and are suppressed during movement and REM sleep.

Optogenetic activation in visual cortex produced rapid increases in delta-band LFP power, stronger spike-field coupling, and heightened spiking synchrony that spread up to a millimetre from the stimulation site and across behavioural states. Electrophysiological recordings confirmed direct, long-range inhibitory postsynaptic currents up to 2 mm away. Pan-cortical chemogenetic activation using a DREADD increased the duration and frequency of slow-wave sleep bouts, shortened sleep latency, and elevated low-frequency cortical activity without affecting the hippocampus. These results establish Sst-Chodl interneurons as a cortical circuit element capable of actively promoting synchrony and sleep, complementing traditional subcortical mechanisms.