title: Fast and slow effects of medial olivocochlear efferent activity in humans.
abstract: BACKGROUND
  The medial olivocochlear (MOC) pathway modulates basilar membrane motion and auditory nerve activity on both a fast (10-100 ms) and a slow (10-100 s) time scale in guinea pigs. The slow MOC modulation of cochlear activity is postulated to aide in protection against acoustic trauma. However in humans, the existence and functional roles of slow MOC effects remain unexplored.
  
  
  RESULTS
  By employing contralateral noise at moderate to high levels (68 and 83 dB SPL) as an MOC reflex elicitor, and spontaneous otoacoustic emissions (SOAEs) as a non-invasive probe of the cochlea, we demonstrated MOC modulation of human cochlear output both on a fast and a slow time scale, analogous to the fast and slow MOC efferent effects observed on basilar membrane vibration and auditory nerve activity in guinea pigs. The magnitude of slow effects was minimal compared with that of fast effects. Consistent with basilar membrane and auditory nerve activity data, SOAE level was reduced by both fast and slow MOC effects, whereas SOAE frequency was elevated by fast and reduced by slow MOC effects. The magnitudes of fast and slow effects on SOAE level were positively correlated.
  
  
  CONCLUSIONS
  Contralateral noise up to 83 dB SPL elicited minimal yet significant changes in both SOAE level and frequency on a slow time scale, consistent with a high threshold or small magnitude of slow MOC effects in humans.
authors.affiliation: Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, Northwestern University, Evanston, Illinois, United States of America. weizhao2008@u.northwestern.edu
authors.forename: Wei
authors.initials: W
authors.lastname: Zhao
authors.forename: Sumitrajit
authors.initials: S
authors.lastname: Dhar
mesh_terms: D000328:Adult; D003051:Cochlea / Q000502:physiology*; D004525:Efferent Pathways / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009622:Noise; D009847:Olivary Nucleus / Q000502:physiology*; D017084:Otoacoustic Emissions, Spontaneous / Q000502:physiology; D055815:Young Adult