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The effect of long-term unilateral deafness on the activation pattern in the auditory cortices of French-native speakers: influence of deafness side.

Hanss J, Veuillet E, Adjout K, Besle J, Collet L, Thai-Van H - BMC Neurosci (2009)

Bottom Line: This was observed not only for AEP amplitudes but also for AEP time course.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Université de Lyon, Lyon, F-69003, France. julien.hanss@hotmail.fr

ABSTRACT

Background: 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.

Results: 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.

Conclusion: 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.

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Related in: MedlinePlus

Mean (± SEM) pure-tone bone conduction hearing thresholds (dB HL) obtained in the damaged ear of the eighteen unilaterally deaf subjects. Profound deafness was found both in the LD-r and the RD-l group.
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Figure 1: Mean (± SEM) pure-tone bone conduction hearing thresholds (dB HL) obtained in the damaged ear of the eighteen unilaterally deaf subjects. Profound deafness was found both in the LD-r and the RD-l group.

Mentions: Thirty-four, (18 unilaterally deaf and 16 normal hearing) right-handed, French-native speakers aged from 27 to 59 years participated in the study. No subject reported any history of neurological impairment or language disorder. All patients had a profound unilateral deafness with bone conduction hearing thresholds on the deaf side worst than 65 dB HL for all frequencies tested between 250 and 8000 Hz (see Figure 1). Normal or subnormal air conduction hearing thresholds (< 25 dB HL) were obtained in their contralateral healthy ear. The control subjects had normal or subnormal air conduction hearing thresholds (< 25 dB HL) in both ears. All subjects were tested on one ear and split into four groups depending on the side of stimulation: normal-hearing subjects tested on the left ear (NH-l, n = 8; mean age ± standard error 42.62 ± 3.04 years; sex ratio= 4 M/4 F), subjects with right-sided deafness tested on the left ear (RD-l, n = 10; 40.3 ± 2.42 years; 8 M/2 F), normal hearing subjects tested on the right ear (NH-r, n = 8; mean age 39.37 ± 2.3 years; 5 M/3 F) and subjects with left-sided deafness tested on the right ear (LD-r, n = 8; 46.37 ± 3.7 years; 4 M/4 F). The groups did not differ significantly for mean age (ANOVA, p = 0.349). The groups of unilaterally deaf subjects did not differ for the mean duration of hearing loss (± standard error, SEM) at the time of testing, which was, respectively, 6.61 ± 3.7 years and 5.51 ± 3.3 years in the LD-r group and the RD-l group. Almost all hearing-impaired individuals (17 out of 18 patients) shared the same aetiology of deafness: i.e., sensorineural hearing loss. The deafness was indeed due to a sudden sensorineural hearing loss for 6 out of 8 patients in the LD-r group and for 8 out of 10 patients in the RD-l group. In addition, three other patients, two in the RD-l group and one in the LD-r group, had developed a sensorineural hearing loss due to an impairment of the inner ear consecutive to a chronic infection of the middle ear (cholesteatoma); in these three subjects, the inner ear damage was either due to the disease (spread of cholesteatoma towards the inner ear) or to the surgical technique. There was only one case of retrocochlear deafness in the LD-r group: this subject developed a sudden unilateral hearing loss after cochlear nerve resection during acoustic neuroma removal.


The effect of long-term unilateral deafness on the activation pattern in the auditory cortices of French-native speakers: influence of deafness side.

Hanss J, Veuillet E, Adjout K, Besle J, Collet L, Thai-Van H - BMC Neurosci (2009)

Mean (± SEM) pure-tone bone conduction hearing thresholds (dB HL) obtained in the damaged ear of the eighteen unilaterally deaf subjects. Profound deafness was found both in the LD-r and the RD-l group.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2662863&req=5

Figure 1: Mean (± SEM) pure-tone bone conduction hearing thresholds (dB HL) obtained in the damaged ear of the eighteen unilaterally deaf subjects. Profound deafness was found both in the LD-r and the RD-l group.
Mentions: Thirty-four, (18 unilaterally deaf and 16 normal hearing) right-handed, French-native speakers aged from 27 to 59 years participated in the study. No subject reported any history of neurological impairment or language disorder. All patients had a profound unilateral deafness with bone conduction hearing thresholds on the deaf side worst than 65 dB HL for all frequencies tested between 250 and 8000 Hz (see Figure 1). Normal or subnormal air conduction hearing thresholds (< 25 dB HL) were obtained in their contralateral healthy ear. The control subjects had normal or subnormal air conduction hearing thresholds (< 25 dB HL) in both ears. All subjects were tested on one ear and split into four groups depending on the side of stimulation: normal-hearing subjects tested on the left ear (NH-l, n = 8; mean age ± standard error 42.62 ± 3.04 years; sex ratio= 4 M/4 F), subjects with right-sided deafness tested on the left ear (RD-l, n = 10; 40.3 ± 2.42 years; 8 M/2 F), normal hearing subjects tested on the right ear (NH-r, n = 8; mean age 39.37 ± 2.3 years; 5 M/3 F) and subjects with left-sided deafness tested on the right ear (LD-r, n = 8; 46.37 ± 3.7 years; 4 M/4 F). The groups did not differ significantly for mean age (ANOVA, p = 0.349). The groups of unilaterally deaf subjects did not differ for the mean duration of hearing loss (± standard error, SEM) at the time of testing, which was, respectively, 6.61 ± 3.7 years and 5.51 ± 3.3 years in the LD-r group and the RD-l group. Almost all hearing-impaired individuals (17 out of 18 patients) shared the same aetiology of deafness: i.e., sensorineural hearing loss. The deafness was indeed due to a sudden sensorineural hearing loss for 6 out of 8 patients in the LD-r group and for 8 out of 10 patients in the RD-l group. In addition, three other patients, two in the RD-l group and one in the LD-r group, had developed a sensorineural hearing loss due to an impairment of the inner ear consecutive to a chronic infection of the middle ear (cholesteatoma); in these three subjects, the inner ear damage was either due to the disease (spread of cholesteatoma towards the inner ear) or to the surgical technique. There was only one case of retrocochlear deafness in the LD-r group: this subject developed a sudden unilateral hearing loss after cochlear nerve resection during acoustic neuroma removal.

Bottom Line: This was observed not only for AEP amplitudes but also for AEP time course.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Université de Lyon, Lyon, F-69003, France. julien.hanss@hotmail.fr

ABSTRACT

Background: 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.

Results: 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.

Conclusion: 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.

Show MeSH
Related in: MedlinePlus