Fast and Slow Components of Auditory Brainstem Response

Frequency Series and Effect of Rise Time

Abstract

Auditory brainstem response (ABR) consists of fast and slow components. In this study, relationship between the two components and stimulus frequency was examined.
ABR recordings were made in 13 normal hearing adults using tone pips of 0.5, 1, 2, 4 and 8kHz with the intensity level of 40dB nHL. Two ways of rise-decay time settings for the tone pips were applied; 4ms at all frequencies and 2 cycles of every chosen frequency (2-0-2 pip).
The slow component and wave V of the fast component showed almost the same latency change: a prolongation of latency with decreasing stimulus frequency.
When the rise-decay time of the tone pips were set into 4ms throughout the frequencies, the amplitude of the slow component decreased with increasing stimulus frequency. On the other hand, there was no such a change in slow component amplitude when 2-0-2 pips were used. The amplitude ratio of wave V to slow component decreased with decreasing stimulus frequency, and remained relatively constant at each frequency regardless of rise-decay time of the stimuli.
These amplitude changes of the slow component can be explained by the effective areas of stimuli for evoking the responses.
Being fixed the rise-decay time to 4ms, the effective stimulus intensity for evoking the response decreases with increasing stimulus frequency because it is only initial half or one cycle of the tone pips which contributes for evoking the response.
Those results suggest that the ever mentioned audiometric difficulty for low frequency regions in ABR is mainly related to the fast component being of low amplitude in the frequency range below 1kHz, and the slow component with relatively large amplitude in low frequency region seems to be highly recommendable for audiometric purposes.