Visceral signals reach visual cortex during slow wave sleep: study in monkeys.

Propagation of signals from the gastro-intestinal system towards the occipital cortex within sleep-wake cycle was investigated in three monkeys used in the study of sleep impairment in a chronic MPTP model of parkinsonism. The monkeys differed in motor abilities and sleep structure. e animal (M1) was non-motor disabled and had no sleep alterations. The other two monkeys were severely motor affected, but one (M2) had normal sleep cycles; meanwhile, the other (M3) had no complete sleep cycles. To evaluate the level of sleep and to record cortical evoked responses screw electrodes were implanted over the occipital cortex. Two hours before overnight recordings, two hook electrodes were injected intraperitoneally (under light Ketanest anesthesia) and anchored in gut. Using these electrodes, electric stimulation was applied during slow wave sleep, and in wakefulness. Cortical evoked responses to intraperitoneal stimulation were found indeed during sleep in experiments with M1 and M2. These results show that also in primates with normal sleep pattern visceral information is transferred to the cerebral cortex during slow wave sleep.