Cortical evoked responses to magnetic stimulation of macaque's abdominal wall in sleep-wake cycle

EEG and eye movements (magnetic search coil method) were recorded in sleep and wakefulness in a monkey (Macaca fascicularis) while the animal was sitting in a primate chair. Single pulse magnetic stimulation was applied to the monkey's abdominal wall using a circular coil and a Magstim 200 stimulator. Magnetic stimuli did not wake the sleeping animal, and being applied during slow wave sleep evoked clear responses in EEG with a latency of 80-100 ms. These responses disappeared during wakefulness and rapid eye movement sleep. Control experiments confirmed that these responses were not caused by the acoustic clicks produced by the magnetic coil. Results of this study further confirm that during sleep, signals from visceral organs reach the cortical areas which in wakefulness process exteroceptive sensory information. This observation indicates that magnetic stimulation may be a useful tool for researching neural connectivity reorganization within the sleep-wake cycle.