| Spontaneous middle ear muscle activity (MEMA), recorded by extratympaic manometry, and EEG, recorded from an array of eight scalp electrodes, were recorded in five human subjects over three consecutive nights of sleep. Phasic, REM sleep MEMA was identified, using an automated peak detection algorithm. The computer-identified onset of MEMA events served as time-markers for automated, offline collection and subsequent averaging of EEG epochs that were time-locked to the occurrence of MEMA. A reliable, averaged, event-related potential (ERP), which began before MEMA onset, was observed regardless of the presence or absence of concurrent eye movements. The scalp distribution of the MEMA-related ERP revealed an area of maximal activity at the vertex and a progressive amplitude diminution with increasing distance from the vertex. The averaged MEMA-related ERP resembled the auditory evoked potential in waveshape, amplitude, duration, and scalp distribution. The MEMA-related ERP may be a human analog of the phasic, "ponto-geniculo-auditory" discharges recorded in cat auditory structures in accompaniment with episodic contractions of the middle ear muscles during REM sleep. The functional significance of the MEMA-related ERP, based upon its scalp distribution, similarities with the human auditory evoked response, and parallels with phasic auditory and acoustomotor activity in animals, was discussed. The MEMA-related ERP may reflect in part neural activity concerned with phasic, brainstem-generated activation of auditory structures during REM sleep. The possibility that the MEMA-related brain activity might represent information processing associated with auditory imagery in dreams was also considered. |
