Habituation of the auditory evoked field component N100m and its dependence on stimulus duration.

OBJECTIVES

In the current study we investigated the habituation of the neuromagnetic auditory evoked field (AEF) component N100m and its dependence on stimulus duration.

METHODS

Fifteen subjects were stimulated monaurally in 3 blocks of 210 trials with 1000 Hz tones of different duration (50, 100, 200 ms) and in a single block of 70 trials with 1200 Hz tones. The order of blocks was counterbalanced within the total experiment. Tones were separated by a stimulus onset asynchrony of 2000 ms. AEF were recorded over both hemispheres by means of a 31 channel system (Philips) on two different days. The AEF were compared within and between the blocks and between the hemispheres. Additionally, the effects of block order were analyzed.

RESULTS

In the course of the experiment a pronounced decrease of N100m mean global field power (MGFP) and an increase of its latency were observed. While the order of blocks clearly affected the degree of habituation, stimulus duration did not have any influence on it. Within the blocks, habituation also had an impact on dipole location in inferior-superior direction. The application of the 1200 Hz stimulus led to a slight response recovery. The change in tone pitch affected the dipole orientation, as an indicator for the tonotopic organization of the auditory cortex.