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For in vivo light stimulation, light-pulse trains were generated via a laser stimulator (SEN-7103, Nihon Kohden, Japan) and output through an isolator (ss-102J, Nihon Kohden, Japan). A rotating optical joint (FRJ_FC-FC, Doric Lenses, Canada) was used to relieve torque and was attached to the external end of the optical fiber. For acute photostimulation, each stimulation epoch was applied 20 s after identifying a stable NREM or REM sleep event by real-time online EEG/EMG analysis. Light-pulse trains (5-ms duration each) were programmed and conducted during the light period, when mice are inactive. The cut-off line for stage transitions was 60 s after the laser was turned on. For chronic photostimulation, programmed light-pulse trains (5-ms pulses at 20 Hz, with 10-s on/ 20-s off for 120 cycles) were used from 09:00 to 10:00. EEG/EMG recordings during the same period on the previous day served as a baseline control. Power intensities of blue or yellow light at the tip of the optical fiber were calibrated to emit 3–7 mW [51 (link)].

All tests were performed during the light period (10:00–19:00). On the morning of the experimental day, a mouse, from its home cage, was transferred to a sound-insulated and temperature-controlled room (23–25°C). An optical cable (Logos, Ibaraki, Japan) was attached to the optical fiber on the animal’s head through a ferrule (KYOCERA) and also connected to a 532-nm DPSS laser (GL532T3-300FC, Shanghai Laser & Optics Century Co., Ltd., China) via a rotary joint (FRJ_FC-FC, Doric Lenses, Quebec, Canada). A flexible electric cable for the piezo sensor was attached to the connector pins on the animal’s head. A minimum period of 4 h was designated for the animal to become habituated to its new environment, and thus, for all physiological parameters to become stable. Continuous recording was then performed until the end of the experiment (from ∼14:00 to ∼19:00). The laser was controlled with an electric stimulator (SEN-3301, Nihon Kohden, Japan) and photo intensity was measured by an optical power meter (PM20, Thorlabs, Newton, NJ, United States).

The optical fiber cannula was attached to a rotating joint (FRJ_FC-FC, Doric Lenses, Canada) to relieve torque. The joint was connected via a fiber to a 473 nm blue laser diode (Newton Inc., Hangzhou, China). Light pulses were generated through a stimulator (SEM-7103 Nihon Kohden, Japan) and output via an isolator (ss-102J, Nihon Kohden). For 1 hr photostimulation, we used programmed light pulse trains (5 ms pulses at 20 Hz for 50 s with 40 s intervals for 1 hr). Light stimulation was conducted from 9 p.m. to 10 p.m. EEG/EMG recorded during the same period on the previous day served as baseline. Light intensity was tested by a power meter (PM10, Coherent) before each experiment and calibrated to emit 20–30 mW/mm² from the tip of the optical fiber cannula.