The post-auricular response. A single motor unit study.

In order to investigate the functional significance of the 'post-auricular response' (PAR), a study was performed on single motor unit (MU) responses recorded by a microelectrode inserted into the retroauricular muscle body. The great variability of the latency of single MUs and the presence of later responses rule out a direct motoneurone activation. Our findings suggest a synchronizing action of acoustic stimuli on the firing of some MUs already present at rest or activated by the train of clicks, with a latency greater than 70 msec. The amplitude of the PAR recorded by surface electrodes and by averaging techniques is connected to the number of MUs synchronized by acoustic stimulation.