Laminar analysis of intracortical auditory evoked potentials during the wakefulness-sleep cycle in the cat.

Click-elicited evoked potentials (EPs) were recorded simultaneously in six different depths of the auditory cortex of freely moving cats during the wakefulness-sleep cycle. Chronically implanted multielectrodes designed especially for this purpose were used. The clicks were given through a bone conductor and middle ear muscles were cut to keep the acoustic input constant. The EPs recorded in different cortical depths changed in different ways during the wakefulness-sleep cycle as evidenced by both the early and middle latency components. The amplitude of the middle latency components was the largest in slow wave sleep (SWS) in all cortical depths. The early deep negative wave was the smallest in paradoxical sleep (PS) probably indicating a reduced sensory input. In the aroused state a negative component of approximately 60 ms appeared localized to the superficial layers. The lack of a true phase reversal of the early components, their independently changing amplitudes and the homogeneous polarity of the later waves in the different cortical depths do not support the idea of simple dipole processes that could explain their generation.