Behavioral States in the Chronic Medullary and Midpontine Cat

Behavioral state organization was studied in the caudal portion of chronically maintained cats with transections at the ponto-medullary junction or midpontine level. The cats spent most of their time in a 'quiescent state.' This state was periodically interrupted by 'phasic activations.' During quiescence, ECG and reticular unit activity rates were low and regular. EMG levels resembled those seen during non-REM sleep in intact cats. During phasic activations, unit activity in the nucleus gigantocellularis and neck EMG activity increased to levels seen in the intact cat during active waking. Gross postural changes, vestibular slow phase head nystagmus and head shake reflexes could be observed at these times. No periods of neck muscle atonia were observed in either state. No periods of brain-stem controlled rapid eye movements (REMs) occurred. Unit activity patterns similar to those seen in the intact cat during REM sleep were never observed. Physostigmine administration did not produce REM sleep signs, but rather, triggered an aroused state. Phasic activations occurred in a regular ultradian rhythm, with a period similar to that seen in the REM sleep cycle. We conclude that the chronic medullary cat retains primitive aroused and quiescent states, but does not have any of the local signs of REM sleep. However, the medulla does have the capability of generating ultradian rhythmicities which may contribute to the control of the basic rest activity cycle and the REM, non-REM sleep cycle.