Evidence for modulation rate specific adaptation in the frequency following response?

Abstract

We used an adaptation paradigm to investigate whether the frequency following response (FFR) would show evidence for neurons tuned to modulation rate in humans, as has been previously shown in the inferior colliculus of the macaque using fMRI [Baumann et al. Nat. Neurosci. 14, 423–425 (2011)]. The FFR to a 100-ms, 75-dB SPL, target complex tone with an envelope rate of 213 Hz was measured for ten subjects. The target was preceded by a 200-ms, 75-dB SPL, adaptor complex with an envelope rate of 90, 213, or 504 Hz. All complexes contained alternating-phase harmonics from approximately 3.9 to 5.4 kHz. A “vertical” montage (+ Fz, - C7, ground = mid-forehead) was used, for which the FFR is assumed to reflect phase-locked neural activity from generators in the rostral brainstem. The results showed significant adaptation effects in the spectral magnitude of the 213-Hz envelope-related component of the FFR. However, the identical-rate adaptor did not generally produce more adaptation than the different-rate adaptors. Hence, the present results do not provide evidence for neurons tuned to modulation rate in the human brainstem. [Work supported by Wellcome Trust Grant 088263.]