Despite significant advances in our understanding of many of the peripheral effects of activating the medial olivocochlera (MOC) efferent fibers to outer hair cells (OHCs), and of the molecular mechanisms underlying those effects, the functional significance of this pathway in human audition remains controversial. In both awake humans and anesthetized animals, the MOC fibers respond to sound, either ipsilaterally or contralaterally delivered, and thus constitute the effector limb of a binaural sound-evoked reflex pathway. However, we don~t know if the basic organizational plan of the reflexes seen in animals applies to human. When activated by sound, MOC fibers alter the state of the OHCs and thereby affect the generation of a variety of otacoustic emissions (OAEs). This phenomenon provides a non-invasive way to examine the activation levels of the MOC pathway. Our approach is to use OAEs to assay MOC activation levels in normal human subjects, and to compare the levels of activation in a variety of listening contexts. We have developed OAE-based methods that allow measurement of MOC activation from any source, including ipsilateral activation which has been difficult to measure in the past. To understand the functional organization of the human MOC system, we will, in humans (Aim 1a) determine the relative strength of the ipsilateral, contralateral and binaural MOC reflexes, (Aim 1b) determine the frequency resolution of the MOC reflexes and (Aim 1c) determine MOC reflex strength across frequency in terms of the underlying changes in cochlear sensitivity. To address the functional significance of the MOC pathway, we will (Aim 2a) measure MOC activation levels in psychophysical tasks in which we predict that MOC activation should aid performance (discrimination of transient signals in noise) and those in which no benefit is anticipated, and (Aim 2b) measure MOC activation levels during selective attention to auditory vs. Visual stimuli or to one component of a complex auditory stimulus. The results of our experiments will provide the first comprehensive assessment of the fractional organization of the human MOC system and should provide significant insight into the functional significance of the MOC system in humans.

Project Start
2000-06-01
Project End
2001-05-31
Budget Start
1998-10-01
Budget End
1999-09-30
Support Year
25
Fiscal Year
2000
Total Cost
$330,060
Indirect Cost
Name
Massachusetts Eye and Ear Infirmary
Department
Type
DUNS #
073825945
City
Boston
State
MA
Country
United States
Zip Code
02114
Gutschalk, Alexander; Oxenham, Andrew J; Micheyl, Christophe et al. (2007) Human cortical activity during streaming without spectral cues suggests a general neural substrate for auditory stream segregation. J Neurosci 27:13074-81
Micheyl, Christophe; Carlyon, Robert P; Gutschalk, Alexander et al. (2007) The role of auditory cortex in the formation of auditory streams. Hear Res 229:116-31
Wilson, E Courtenay; Melcher, Jennifer R; Micheyl, Christophe et al. (2007) Cortical FMRI activation to sequences of tones alternating in frequency: relationship to perceived rate and streaming. J Neurophysiol 97:2230-8
Fullerton, Barbara C; Pandya, Deepak N (2007) Architectonic analysis of the auditory-related areas of the superior temporal region in human brain. J Comp Neurol 504:470-98
Sigalovsky, Irina S; Melcher, Jennifer R (2006) Effects of sound level on fMRI activation in human brainstem, thalamic and cortical centers. Hear Res 215:67-76
Sigalovsky, Irina S; Fischl, Bruce; Melcher, Jennifer R (2006) Mapping an intrinsic MR property of gray matter in auditory cortex of living humans: a possible marker for primary cortex and hemispheric differences. Neuroimage 32:1524-37
Hawley, Monica L; Melcher, Jennifer R; Fullerton, Barbara C (2005) Effects of sound bandwidth on fMRI activation in human auditory brainstem nuclei. Hear Res 204:101-10
Harms, Michael P; Guinan Jr, John J; Sigalovsky, Irina S et al. (2005) Short-term sound temporal envelope characteristics determine multisecond time patterns of activity in human auditory cortex as shown by fMRI. J Neurophysiol 93:210-22
Talavage, Thomas M; Edmister, Whitney B (2004) Nonlinearity of FMRI responses in human auditory cortex. Hum Brain Mapp 22:216-28
Penagos, Hector; Melcher, Jennifer R; Oxenham, Andrew J (2004) A neural representation of pitch salience in nonprimary human auditory cortex revealed with functional magnetic resonance imaging. J Neurosci 24:6810-5

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