Far-field recorded frequency-following responses: evidence for the locus of brainstem sources.

Two experiments were performed to determine the brainstem origins of the scalp recorded auditory frequency-following response (FFR). The first was a study of FFR onset latency in which responses observed by direct recording from depth electrodes in brainstem auditory nuclei were compared with those obtained from the scalp. The mean onset latency of scalp recorded FFR (5.8 msec) closely approximated the 5.4 msec mean latency of response recorded from within the inferior colliculus (IC). In a second experiment, cooling of the IC greatly reduced or eliminated FFR both within this nucleus and at the scalp. FFR at the medial superior olive was unaffected during cooling. It was concluded that at moderate intensities of stimulation the primary source of scalp recorded FFR is the IC.