In-vivo measurement of sound-induced motions in the gerbil cochlea

We developed methods to measure sound-induced motions in a live mammalian cochlea using a laser Doppler velocimeter (LDV). We measured the basilar membrane (BM) in the Mongolian gerbil at a distance of roughly 1.5 mm from the extreme base and found a best frequency (BF) of roughly 35 kHz. We chose the base to gain access through the round window membrane (RWM) to minimize the need for invasive surgery. Post-mortem measurements showed a 20dB drop in sensitivity as well as a half-octave drop in BF. The post-mortem phase led the in vivo phase below the BF and lagged the in vivo phase above the BF. These features of the post-mortem response agree with those seen by Overstreet [10] in the base of the gerbil cochlea. To look for evidence of radial modes in the BM, we measured points along the radius of the BM both in vivo and post-mortem. In the in vivo case, we found slightly sharper tuning in the center of the BM than on the edge but similar phase excursions. In the post-mortem case, we found similar bandwidths and phase excursions along the radius of the BM. Since in vivo measurements along the radius of the BM were only collected in one animal, we cannot yet conclude that there are multiple radial modes in the gerbil BM. In addition, our in vivo preparation was relatively insensitive as evidenced by compound action potential (CAP) thresholds greater than 80dB SPL in the region of interest.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2010

Author dc:creator

• Farrahi, Shirin

Advisor dc:contributor.advisor

• Dennis M. Freeman.

• Electrical Engineering and Computer Science.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/58177

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/58177