Optogenetic inhibition of the dorsal–intermediate lateral septum (LS) γ-aminobutyric acid–mediated (GABAergic) neurons during the awake state promoted non–rapid eye movement (NREM)–like sleep state and prolonged emergence time. (A) Schematic of optogenetic inactivation of the dorsal–intermediate lateral septum GABAergic neurons and electroencephalogram (EEG)/electromyography (EMG) recordings. (B) Typical photomicrographs showing enhanced yellow fluorescent protein (eYFP)-labeled dorsal–intermediate lateral septum cells. Scale bar, 100 μm. (C) Example traces of firings showing that optical stimulation reliably inhibited the firing activities of NpHR-eYFP neurons. (D) Representative EEG/EMG traces and EEG heat map for NpHR-eYFP. Animals showing changes in EEG oscillation, EMG, and correspondent heat map EEG power spectrum in response to local optical silencing (yellow light stimulation, 593 nm) during the awake state. (E) Awake-to-sleep transitions after optogenetic stimulation at 20 Hz. U = 0.00, P < 0.001, Mann–Whitney rank sum test (two-tailed). (F through I) Summary showing increased normalized relative cortical EEG spectral delta power and decreased beta and gamma power. Unpaired two-tailed t test. Delta: t₁₂ = 3.47, P = 0.005; theta: t₁₂ = 1.70, P = 0.114; beta: t₁₂ = 4.55, P < 0.001; gamma: t₁₂ = 6.99, P < 0.001. (J) Representative EEG/EMG traces and heat map of EEG power spectra showing that acute photostimulation applied during the awake state induced a transition to non-REM sleep in the NpHR-eYFP mouse. (K through M) Summary data showing that burst numbers, burst duration, and burst suppression ratio (BSR) did not change during periods of 20-Hz optical stimulation. Unpaired two-tailed t test. Number of bursts: t₁₀ = 0.07, P = 0.944; burst duration: t₁₀ = 0.37, P = 0.721; burst suppression ratio: t₁₀ = 0.29, P = 0.780. (N) Left: Diagram for optical stimulation and recording of emergence time. Laser stimulation was initiated after turning off isoflurane administration and ended with recovery of righting. Right: Summary showing that optical inactivation of dorsal–intermediate lateral septum GABAergic neurons prolonged emergence time from 1.5% isoflurane anesthesia. t₁₀ = 5.45, P < 0.001, unpaired two-tailed Student’s t test. The data represent means ± SD. **P < 0.01; ***P < 0.001. DAPI, 4′,6-diamidino-2-phenylindole; LV, lateral ventricle.