Front Syst Neurosci. 2015 Feb 25;9:12. doi: 10.3389/fnsys.2015.00012. eCollection 2015.
The biological role of the medial olivocochlear efferents in hearing: separating evolved function from exaptation.
Frontiers in systems neuroscience
David W Smith, Andreas Keil
Affiliations
Affiliations
- Program in Behavioral and Cognitive Neuroscience, Department of Psychology, University of Florida Gainesville, FL, USA ; Center for Smell and Taste, University of Florida Gainesville, FL, USA.
- Program in Behavioral and Cognitive Neuroscience, Department of Psychology, University of Florida Gainesville, FL, USA ; Center for the Study of Emotion and Attention, University of Florida Gainesville, FL, USA.
PMID: 25762901
PMCID: PMC4340171 DOI: 10.3389/fnsys.2015.00012
Abstract
Cochlear outer hair cells (OHCs) are remarkable, mechanically-active receptors that determine the exquisite sensitivity and frequency selectivity characteristic of the mammalian auditory system. While there are three to four times as many OHCs compared with inner hair cells, OHCs lack a significant afferent innervation and, instead, receive a rich efferent innervation from medial olivocochlear (MOC) efferent neurons. Activation of the MOC has been shown to exert a considerable suppressive effect over OHC activity. The precise function of these efferent tracts in auditory behavior, however, is the matter of considerable debate. The most frequent functions assigned to the MOC tracts are to protect the cochlea from traumatic damage associated with intense sound and to aid the detection of signals in noise. While considerable evidence shows that interruption of MOC activity exacerbates damage due to high-level sound exposure, the well characterized MOC physiology and evolutionary studies do not support such a role. Instead, a MOC protective effect is well explained as being a byproduct of the suppressive nature of MOC action on OHC mechanical behavior. A role in the enhancement of signals in noise backgrounds, on the other hand, is well supported by (1) an extensive physiological literature (2) examination of naturally occurring environmental acoustic conditions (3) recent data from multiple laboratories showing that the MOC plays a significant role in auditory selective attention by suppressing the response to unattended or ignored stimuli. This presentation will argue that, based on the extant literature combining the suppression of background noise through MOC-mediated rapid adaptation (RA) with the suppression of non-attended signals, in concert with the corticofugal pathways descending from the auditory cortex, the MOC system has one evolved function-to increase the signal-to-noise ratio, aiding in the detection of target signals. By contrast, the MOC system role in reducing noise damage and the effects of aging in the cochlea may well represent an exaptation, or evolutionary "spandrel".
Keywords: MOC; OHC; auditory attention; corticofugal pathways; medial olivocochlear efferents; outer hair cells; protection from acoustic trauma; signal-to-noise ratio
References
- Cereb Cortex. 2005 Oct;15(10):1609-20 - PubMed
- Proc Natl Acad Sci U S A. 1997 Sep 30;94(20):10750-5 - PubMed
- Int J Psychophysiol. 1994 Aug;17(3):281-9 - PubMed
- Curr Opin Otolaryngol Head Neck Surg. 2010 Oct;18(5):447-53 - PubMed
- Brain Res. 1970 Jun 30;21(1):135-7 - PubMed
- J Assoc Res Otolaryngol. 2003 Dec;4(4):445-65 - PubMed
- Hear Res. 1997 Jan;103(1-2):101-22 - PubMed
- J Neurophysiol. 1997 Dec;78(6):3095-106 - PubMed
- PLoS One. 2007 Sep 19;2(9):e909 - PubMed
- J Neurophysiol. 1987 Apr;57(4):1002-21 - PubMed
- J Neurosci. 2013 Mar 27;33(13):5542-52 - PubMed
- Mitochondrion. 2014 Jul;17:126-31 - PubMed
- J Neurosci. 2011 May 4;31(18):6759-63 - PubMed
- Psychophysiology. 2001 Jan;38(1):35-40 - PubMed
- J Acoust Soc Am. 1991 Jun;89(6):2837-42 - PubMed
- J Neurophysiol. 1988 Aug;60(2):549-68 - PubMed
- Nat Rev Neurosci. 2004 Apr;5(4):279-90 - PubMed
- Neuroscience. 2001;104(2):347-58 - PubMed
- Eur J Neurosci. 2014 Dec;40(12):3785-92 - PubMed
- Hear Res. 2007 Nov;233(1-2):117-23 - PubMed
- J Acoust Soc Am. 1996 Jun;99(6):3572-84 - PubMed
- Neuroscience. 2012 Oct 25;223:325-32 - PubMed
- Clin Exp Pharmacol Physiol. 2009 Jul;36(7):603-11 - PubMed
- Cereb Cortex. 2006 Jul;16(7):941-8 - PubMed
- J Neurosci. 2014 Mar 26;34(13):4599-607 - PubMed
- Neuron. 2009 Jan 29;61(2):168-85 - PubMed
- Science. 1980 Oct 3;210(4465):71-2 - PubMed
- Proc Natl Acad Sci U S A. 1996 Nov 26;93(24):13494-9 - PubMed
- . 1995 Jan 1;1(4):385-400 - PubMed
- Hear Res. 1988 Sep 15;35(2-3):165-89 - PubMed
- Electroencephalogr Clin Neurophysiol Suppl. 1987;40:146-54 - PubMed
- Brain Res. 1988 May 3;447(2):380-3 - PubMed
- Brain Res. 1994 Jan 7;633(1-2):353-6 - PubMed
- PLoS Comput Biol. 2009 Jul;5(7):e1000444 - PubMed
- J Neurosci. 2007 Apr 11;27(15):4146-53 - PubMed
- Hear Res. 2003 Aug;182(1-2):140-52 - PubMed
- J Neurophysiol. 1993 Dec;70(6):2519-32 - PubMed
- Int J Psychophysiol. 1992 May;12(3):233-5 - PubMed
- Front Psychol. 2012 Feb 13;3:30 - PubMed
Publication Types
Grant support