To investigate the long-term cortical changes in auditory evoked potential (AEP) asymmetries associated with profound unilateral deafness.
Electroencephalographic (EEG) recordings from 68 channels were used to measure auditory cortex responses to monaural stimulation from 7 unilaterally deaf patients and 7 audiogram-matched controls. Source localization of the AEP N100 response was carried out and regional source waveform amplitude and latency asymmetries were analysed for activity in the N100 latency range and for the middle latency response (MLR) range.
Asymmetry indices (contralateral-ipsilateral)/(contralateral+ipsilateral) showed that matched control subjects, like normally hearing participants, produced activity in the N100 latency range that was more contralaterally dominant for left compared to right ear stimulation. Contrary to expectation, source waveforms and asymmetry indices in the MLR and N100 latency range were similar for unilaterally deaf patients, their matched controls and a group of normally hearing participants.
Regional source waveform analysis revealed no evidence of systematic cortical changes in hemispheric asymmetries associated with long-term unilateral deafness. It is possible that a reorganization of cortical asymmetries to a 'normal' pattern had taken place in the years between deafness and testing.
Electrophysiological measures of auditory hemispheric asymmetries do not suggest long-term cortical reorganisation as a result of profound unilateral deafness.
"~biocog/content/widmann/eeglab-plugins/). For the analysis of the middle-latency components, data were filtered from 20 to 80 Hz (cf., Hine et al., 2008); for the analysis of the late event-related components we used a filter range of 0.1–40 Hz. Artifact rejection was based on independent component analysis (ICA). "
[Show abstract][Hide abstract] ABSTRACT: Change deafness describes the failure to perceive even intense changes within complex auditory input, if the listener does not attend to the changing sound. Remarkably, previous psychophysical data provide evidence that this effect occurs independently of successful stimulus encoding, indicating that undetected changes are processed to some extent in auditory cortex. Here we investigated cortical representations of detected and undetected auditory changes using electroencephalographic (EEG) recordings and a change deafness paradigm. We applied a one-shot change detection task, in which participants listened successively to three complex auditory scenes, each of them consisting of six simultaneously presented auditory streams. Listeners had to decide whether all scenes were identical or whether the pitch of one stream was changed between the last two presentations. Our data show significantly increased middle-latency Nb responses for both detected and undetected changes as compared to no-change trials. In contrast, only successfully detected changes were associated with a later mismatch response in auditory cortex, followed by increased N2, P3a and P3b responses, originating from hierarchically higher non-sensory brain regions. These results strengthen the view that undetected changes are successfully encoded at sensory level in auditory cortex, but fail to trigger later change-related cortical responses that lead to conscious perception of change.
"Such differences between right and left ear stimulation have been previously reported with pure tones in normal hearing subjects. Recent AEP data (auditory N100) from Hine et al.  revealed, in normal hearing subjects stimulated with 1 kHz tone and white noise, a more contralaterally dominant activity for left compared to right ear stimulation. Whereas monaural stimulation with 1 kHz tones yielded a significantly stronger mean N100m dipole moment over the contralateral hemisphere in response to left-ear stimulation, the mean N100m dipole moment was stronger over the ispilateral hemisphere for right-ear stimulation (MEG data from Vasama and Makela ). "
[Show abstract][Hide abstract] ABSTRACT: In normal-hearing subjects, monaural stimulation produces a normal pattern of asynchrony and asymmetry over the auditory cortices in favour of the contralateral temporal lobe. While late onset unilateral deafness has been reported to change this pattern, the exact influence of the side of deafness on central auditory plasticity still remains unclear. The present study aimed at assessing whether left-sided and right-sided deafness had differential effects on the characteristics of neurophysiological responses over auditory areas. Eighteen unilaterally deaf and 16 normal hearing right-handed subjects participated. All unilaterally deaf subjects had post-lingual deafness. Long latency auditory evoked potentials (late-AEPs) were elicited by two types of stimuli, non-speech (1 kHz tone-burst) and speech-sounds (voiceless syllable/pa/) delivered to the intact ear at 50 dB SL. The latencies and amplitudes of the early exogenous components (N100 and P150) were measured using temporal scalp electrodes.
Subjects with left-sided deafness showed major neurophysiological changes, in the form of a more symmetrical activation pattern over auditory areas in response to non-speech sound and even a significant reversal of the activation pattern in favour of the cortex ipsilateral to the stimulation in response to speech sound. This was observed not only for AEP amplitudes but also for AEP time course. In contrast, no significant changes were reported for late-AEP responses in subjects with right-sided deafness.
The results show that cortical reorganization induced by unilateral deafness mainly occurs in subjects with left-sided deafness. This suggests that anatomical and functional plastic changes are more likely to occur in the right than in the left auditory cortex. The possible perceptual correlates of such neurophysiological changes are discussed.
"First, while implanted children only received monaural stimulation, the NH subjects received binaural stimulation. While it is possible that monaural stimulation of the NH subjects could have revealed unilateral hemispheric activity, evidence inferred from previous studies revealing bilateral activity to monaural stimulation would suggest this is not the case (Hine et al., 2008; Ponton et al., 2001). "
[Show abstract][Hide abstract] ABSTRACT: Congenital deafness leads to atypical organization of the auditory nervous system. However, the extent to which auditory pathways reorganize during deafness is not well understood. We recorded cortical auditory evoked potentials in normal hearing children and in congenitally deaf children fitted with cochlear implants. High-density EEG and source modeling revealed principal activity from auditory cortex in normal hearing and early implanted children. However, children implanted after a critical period of seven years revealed activity from parietotemporal cortex in response to auditory stimulation, demonstrating reorganized cortical pathways. Reorganization of central auditory pathways is limited by the age at which implantation occurs, and may help explain the benefits and limitations of implantation in congenitally deaf children.
Brain research 09/2008; 1239:56-65. DOI:10.1016/j.brainres.2008.08.026 · 2.84 Impact Factor
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