Article
Cortical plasticity in unilateral congenital deafness
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Published: | August 25, 2010 |
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Outline
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Previous studies from our lab have shown that sensitivity to interaural time differences (ITD) presented through binaural cochlear implants (CIs) is rudimentary preserved in absence of auditory experience [1], even though the sensitivity to this cue is reduced and cortical aural representation affected by deafness (ibid., [2]). Rare cases in the white cat colony are born with normal unilateral hearing and complete deafness on the other ear. These cases provide an exceptional opportunity for investigation of effects of congenital unilateral (lifelong) experience on sensitivity to electrically-presented binaural cues (through binaural CIs). Approximately 120 unit recordings per animal were obtained from the cortices ipsi- as well as contralateral to the deaf ear. In adult unilaterally-deaf animals, when compared to hearing cats, the same number of responsive units were found (~90%), whereas in binaurally-deaf animals significantly less recording sites (~57%) did respond to CI stimulation. There was, however, less sensitivity to ITD in unilaterally deaf animals than in binaurally deaf animals. Those units that were sensitive to binaural cues in unilaterally-deaf showed no physiological preference to certain binaural parameters, which was different from both binaurally deaf and hearing animals. In consequence, the binaural sensitivity disappeared nearly completely in monaurally deaf animals, despite the fact that non-specific deficits found in binaural deafness were compensated by unilateral hearing.
This demonstrates the extensive and beneficial auditory reorganization in unilaterally deaf that allows to process sensory input by both brain hemispheres; however, at the same time, congenital unilateral deafness has detrimental effects on binaural feature sensitivity and degrades the sensitivity to the deaf ear.
Supported by DFG (Kr 3370/1-1 and 1-2) & MedEl Comp.
References
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- Tillein J, Hubka P, Syed E, Hartmann R, Engel AK, Kral A. Cortical representation of interaural time difference in congenital deafness. Cereb Cortex. 2010;20(2):492-506. DOI: 10.1093/cercor/bhp222
- 2.
- Kral A, Tillein J, Hubka P, Schiemann D, Heid S, Hartmann R, Engel AK. Spatiotemporal patterns of cortical activity with bilateral cochlear implants in congenital deafness. J Neurosci. 2009;29(3):811-27. DOI: 10.1523/JNEUROSCI.2424-08.2009