Modulation of Auditory Evoked Magnetic Fields Elicited by Successive Frequency-Modulated (FM) Sweeps.

Hidehiko Okamoto,Ryusuke Kakigi

doi:10.3389/fnhum.2017.00036

Abstract

In our daily life, we are successively exposed to frequency-modulated (FM) sounds that play an important role in speech and species-specific communication. Previous studies demonstrated that repetitive exposure to identical pure tones resulted in decreased neural activity. However, the effects of repetitively presented FM sounds on neural activity in the human auditory cortex remain unclear. In the present study, we used magnetoencephalography to investigate auditory evoked N1m responses elicited by four successive temporally repeated and superimposed FM sweeps in three sequences: (1) four FM sweeps were identical, (2) four FM sweeps had the same FM direction and rate, but different carrier frequencies, (3) four FM sweeps differed with respect to the FM rate and/or direction and their carrier frequencies. In contrast to our expectations, the results obtained demonstrated that N1m responses were maximal when the four FM sweeps were identical and minimal when they were distinct. These results suggest that the neural processing of repetitive FM sweeps in the human auditory cortex may differ from that of repetitive pure tones.

Highlights

In daily life, we are continually exposed to repetitive sound signals, such as the ticking of a clock, that are irrelevant for listeners
Even though adaptive phenomena may be observed over long timescales such as the evolution of a species, we focused on the neural adaptation that occurs within the timescales of hundreds of Neural Modulation of FM sweeps ms to seconds in the present study
The results obtained demonstrated that the N1m source strengths elicited by test stimuli (TS) were significantly influenced by the sequence of the FM sweep presentation

Summary

Introduction

We are continually exposed to repetitive sound signals, such as the ticking of a clock, that are irrelevant for listeners. These sound signals are ignored and neural resources are conserved for unexpected changes in the acoustic environment (Bregman, 1990). The decrements elicited in neural activity by repetitive auditory signals appear to play an important role in this process. Most of the previous studies that investigated stimulusspecific adaptation used simple pure tones as sound stimuli; neural decrements induced by repetitive complex sound signals remain elusive

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