Delay and temporal integration in medial olivocochlear bundle activation in humans

Citation
S. Maison et al., Delay and temporal integration in medial olivocochlear bundle activation in humans, EAR HEAR, 22(1), 2001, pp. 65-74
Citations number
61
Categorie Soggetti
Otolaryngology
Journal title
EAR AND HEARING
ISSN journal
01960202 → ACNP
Volume
22
Issue
1
Year of publication
2001
Pages
65 - 74
Database
ISI
SICI code
0196-0202(200102)22:1<65:DATIIM>2.0.ZU;2-N
Abstract
Objective: Contralateral suppression of the transient-evoked otoacoustic em issions (TEOAEs) provides a means of studying auditory efferent function, b ut the temporal dynamics of the reflex are not fully understood. The most f undamental parameter is the time-course of activation of contralateral supp ression. The stimulus parameters are likely to be important; this may inclu de temporal dynamics of the suppressor itself. This investigation thus was devoted to the further study of 1) delay of contralateral suppression of TE OAEs-effect of delay of the ipsilateral probe-and 2) temporal variation of the suppressor-effect of amplitude modulation of the contralateral noise st imulus. Design: Measurements were made in three samples of normal-hearing subjects (N-total = 71), employing well-established methods of TEOAE assessment. Results: Statistically significant contralateral suppression occurred some 60 msec after onset of the contralateral noise; thereafter, the effect was essentially constant (i.e., to >180 msec). The results for click delays les s than 60 msec, nevertheless, were systematic and readily fitted by a slopi ng straight line (dB suppression versus time) reminiscent of the concept of threshold power integration. The onset of suppression may thus be characte rized by a time constant. The delay of suppression also was found to be red uced by contralateral amplitude-modulated noise. Conclusions: These findings reinforce a growing consensus in the literature that, despite initiation perhaps some milliseconds after onset of the cont ralateral stimulus, there is a substantial delay, i.e., in the tens of mill iseconds, before maximal suppression is achieved. The exact time constant o f this effect appears to depend upon the combination of probe and suppresso r levels, including the temporality of the suppressor. These factors are li kely to delimit the role/influence of this reflex in real-world function, f avoring perhaps more-or-less sustained suppression that is activated in a t ime-varying sound environment.