Central visual pathways and the distribution of sleep in 24-hr and 1-hr light-dark cycles

The role of the central visual pathways in determining the distribution of sleep in light-dark (LD) cycles in the circadian and ultradian range was examined. EEG, EMG, and brain temperature were recorded under 24-hr (LD 12:12 or LD 10:14) and 1-hr (LD 0.5:0.5) cycles in rats which received either (1) no lesion, (2) primary optic tract lesions, (3) lesions of dorsal and lateral terminal nuclei of the accessory optic system, (4) lesions of medial terminal nucleus of the accessory optic system, or (5) retinohypothalamic tract-suprachiasmatic nucleus lesions. Under 24-hr cycles, about 40% of sleep occurred in the dark in intact rats. Retinohypothalamic tract-suprachiasmatic nucleus lesions abolished this entrainment of sleep to the LD cycle. Under 1-hr cycles, 90% of REM sleep occurred in the dark periods in intact rats. While primary optic tract lesions attenuated this response, it was not completely abolished by any of the visual system lesions. The characteristic LD distributions of sleep in circadian and ultradian cycles may therefore be under separate neural control by the central visual system.