Abstract
The present study investigates the hemispheric contributions of neuronal reorganization following early single-sided hearing (unilateral deafness). The experiments were performed on ten cats from our colony of deaf white cats. Two were identified in early hearing screening as unilaterally congenitally deaf. The remaining eight were bilaterally congenitally deaf, unilaterally implanted at different ages with a cochlear implant. Implanted animals were chronically stimulated using a single-channel portable signal processor for two to five months. Microelectrode recordings were performed at the primary auditory cortex under stimulation at the hearing and deaf ear with bilateral cochlear implants. Local field potentials (LFPs) were compared at the cortex ipsilateral and contralateral to the hearing ear. The focus of the study was on the morphology and the onset latency of the LFPs. With respect to morphology of LFPs, pronounced hemisphere-specific effects were observed. Morphology of amplitude-normalized LFPs for stimulation of the deaf and the hearing ear was similar for responses recorded at the same hemisphere. However, when comparisons were performed between the hemispheres, the morphology was more dissimilar even though the same ear was stimulated. This demonstrates hemispheric specificity of some cortical adaptations irrespective of the ear stimulated. The results suggest a specific adaptation process at the hemisphere ipsilateral to the hearing ear, involving specific (down-regulated inhibitory) mechanisms not found in the contralateral hemisphere. Finally, onset latencies revealed that the sensitive period for the cortex ipsilateral to the hearing ear is shorter than that for the contralateral cortex. Unilateral hearing experience leads to a functionally-asymmetric brain with different neuronal reorganizations and different sensitive periods involved.
Highlights
In developmental manipulations of the symmetry of auditory input, as occurs with unilateral deafness (Reale et al, 1987; Vale et al, 2004; Langers et al, 2005; Burton et al, 2012; Kral et al, 2013) or asymmetric moderate hearing loss (King et al, 2001; Popescu and Polley, 2010), the hemispheres can be differentiated in respect of the anatomical relationship to the hearing ear
The present study investigates whether the function of the primary field A1 of the ipsilateral and the contralateral cortex differs in unilateral deafness
The present comparisons concentrated on Local field potentials (LFPs) morphology and onset latency
Summary
In developmental manipulations of the symmetry of auditory input, as occurs with unilateral deafness (Reale et al, 1987; Vale et al, 2004; Langers et al, 2005; Burton et al, 2012; Kral et al, 2013) or asymmetric moderate hearing loss (King et al, 2001; Popescu and Polley, 2010), the hemispheres can be differentiated in respect of the anatomical relationship to the (better) hearing ear. The ipsilateral cortex receives asymmetric input and likely participates in behavioral consequences of unilateral hearing. The present study investigates whether the function of the primary field A1 of the ipsilateral and the contralateral cortex differs in unilateral deafness. The primary auditory cortex contains mainly binaural neurons—neurons responsive to stimulation of only one ear are virtually absent (Zhang et al, 2004). Stimulation of one ear most frequently leads to excitation in the neurons of the contralateral cortex but may cause excitation or inhibition in the ipsilateral cortex (Imig and Adrián, 1977). Because of the stronger responses at the contralateral cortex, and because of the shorter latency of the responses at the contralateral cortex, the term “aural dominance” (Imig and Adrián, 1977) or aural preference (Kral et al, 2013) has been introduced. Contralateral “dominance” is the consequence of the cortical representation of the contralateral acoustic hemifield
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
