Changes in cochlear mechanics during vocalization: evidence for a phasic medial efferent effect.
Level 5 - mechanism / opinion, no new human data
Animal physiological experiment
PubMed 9714576 · doi:10.1016/s0378-5955(98)00078-1
What was done
Researchers measured cochlear mechanics in 3 mustached bats (Pteronotus p. parnellii) chronically implanted with electrodes during communication vocalizations. Tone pips (1–2 ms) presented every 200 ms evoked cochlear microphonic (CM) potentials, from which the computer extracted decay time (DT) and cochlear resonance frequency (CRF) relative to vocalizations detected by a microphone. Measurements were also obtained following gentamicin administration to inhibit medial olivocochlear (MOC) efferents.
What was found
In all 3 bats, cochlear damping increased during vocalization. In a representative bat, mean DT decreased by 46% from 2.33 ± 0.25 ms during quiet periods to 1.26 ± 0.75 ms during vocalizations. DT suppression occasionally began immediately before vocalization onset; recovery to baseline ranged from milliseconds to 1–2 seconds. Changes in CRF occurred during vocalizations, but the magnitude and direction were unpredictable. After gentamicin administration, DT reduction during vocalization was still present but less pronounced.
Why it matters
This study provides evidence of dynamic, pre-vocal modulation of cochlear mechanics, suggesting central synkinetic efferent control protects or adjusts hearing during self-generated vocalizations.
Limits
Sample size was extremely small (n = 3 bats) in a specialized echolocating species whose extreme cochlear resonance may not generalize to other mammals. Resonant frequency shifts were inconsistent across measurements, and gentamicin did not completely eliminate damping changes, leaving the potential contribution of middle ear muscle reflexes unresolved.
Cited by
- supports The brain has an active mechanism that attenuates auditory transduction immediately before vocalization so individuals do not experience their own voice as overly loud.