Unilateral Auditory Deprivation Research Articles

Hearing aid fitting and unilateral auditory deprivation: behavioral and electrophysiologic assessment

The phenomenon of Late-Onset Unilateral Auditory Deprivation was first reported in 1984. However, a high number of unilateral hearing aid fittings are still carried out in cases of bilateral hearing loss, justified by non-auditory factors such as cost, vanity, misinformation and public health policies. ObjectiveTo carry out behavioral and electrophysiological assessment of the auditory performance of adults using unilateral amplification compared with individuals exposed to bilateral symmetric auditory stimulation. MethodThirty five adults, all with symmetric bilateral sensorineural hearing loss, regular users of unilateral hearing aid, bilateral hearing aids and not users of hearing aids, were assessed on behavioral and electrophysiological tests. ResultsVariance analysis revealed that in the unilaterally fitted group, P300 latency was significantly greater in ears with auditory deprivation compared with those fitted with the hearing aid (p < 0.05). This same group also had poorer performance on the Sentence Recognition Test in Noise held in free field. ConclusionThese results corroborate findings in the literature showing that unilateral auditory deprivation can lead to physiological and perceptual changes.

Cortical auditory evoked responses from an implanted ear after 50 years of profound unilateral deafness

A male with unilateral deafness in the right ear since 8 years of age developed a sudden hearing loss in the left ear at age 63. A hearing aid was fitted in the left ear with limited benefit. The right ear received a cochlear implant (CI) 20 months later. Cortical auditory evoked potentials (CAEPs) and speech recognition scores (SRS) were measured in free-field three, six and nine months after implantation with the hearing aid alone, CI alone and bimodal condition (hearing aid and CI together). Three months after implantation the cortical responses for the two ears were similar, despite more than 50 years of unilateral auditory deprivation. CAEPs measured over time show evidence of binaural interaction and improvements in SRS. Copyright © 2007 John Wiley & Sons, Ltd.

Cortical auditory evoked responses from an implanted ear after 50 years of profound unilateral deafness

A male with unilateral deafness in the right ear since 8 years of age developed a sudden hearing loss in the left ear at age 63. A hearing aid was fitted in the left ear with limited benefit. The right ear received a cochlear implant (CI) 20 months later. Cortical auditory evoked potentials (CAEPs) and speech recognition scores (SRS) were measured in free-field three, six and nine months after implantation with the hearing aid alone, CI alone and bimodal condition (hearing aid and CI together). Three months after implantation the cortical responses for the two ears were similar, despite more than 50 years of unilateral auditory deprivation. CAEPs measured over time show evidence of binaural interaction and improvements in SRS. Copyright © 2007 John Wiley & Sons, Ltd.

Modulation of inhibitory and excitatory synaptic transmission in rat inferior colliculus after unilateral cochleectomy: An in situ and immunofluorescence study

We investigated whether inhibitory synaptic transmission mediated through glycinergic receptor, GABA A receptors, glutamic acid decarboxylase, the enzyme synthesizing GABA, and excitatory synaptic transmission through α-amino-3-hydroxi-5-methylisoxazole-4-propionic acid receptors and N-methyl- d-aspartate receptors are affected in the inferior colliculus by unilateral surgical cochleectomy. In situ hybridization and immunohistofluorescence studies were performed in normal and lesioned adult rats at various times following the lesion (1–150 days). Unilateral auditory deprivation decreased glycine receptor α1 and glutamic acid decarboxylase 67 expression in the contralateral central nucleus of the inferior colliculus. This decrease began one day after cochleectomy, and continued until day 8; thereafter expression was consistently low until day 150. The glycine receptor α1 subunit decrease did not occur if a second contralateral cochleectomy was performed either on day 8 or 150 after the first cochleectomy. Bilateral cochleectomy caused also a bilateral inferior colliculus diminution of glutamic acid decarboxylase 67 mRNA at post-lesion day 8 but there were no changes in glycine receptor α1 compared with controls. In contrast, the abundance of other α2–3, and β glycine receptor, gephyrin, the anchoring protein of glycine receptor, the α1, β2 and γ2 subunits of GABA A receptors, GluR2, R3 subunits of α-amino-3-hydroxi-5-methylisoxazole-4-propionic acid receptors, and NR1 and NR2A transcripts of N-methyl- d-aspartate receptors was unaffected during the first week following the lesion. Thus, unilateral cochlear removal resulted in a selective and long-term decrease in the amount of the glycine receptor α1 subunit and of glutamic acid decarboxylase 67 in the contralateral central nucleus of the inferior colliculus. These changes most probably result from the induced asymmetry of excitatory auditory inputs into the central nucleus of the inferior colliculus and may be one of the mechanisms involved in the tinnitus frequently encountered in patients suffering from a sudden hearing loss.

Early unilateral auditory deprivation increases 2-deoxyglucose uptake in contralateral auditory cortex of juvenile Mongolian gerbils

The effects of early onset, unilateral conductive hearing loss on tone-induced 2-deoxyglucose (2-DG) uptake in the auditory cortex of juvenile Mongolian gerbils ( Meriones unguiculatus) were studied. Atresia of the left ear canal was induced at postnatal day 9 (P9) to achieve reversible auditory deprivation prior to onset of hearing (around P12). Atresia either persisted (ATR, n=4) or the canal was opened 15 min before the 2-DG experiments (RE, n=4) at P27. Control animals were either non-deprived (CON, n=4), or their left ears were plugged acutely (PAX, n=4). In PAX, 2-DG uptake in primary auditory cortex (AI) and anterior auditory field (AAF) was lower in right than in left AI and AAF. In contrast, in ATR and RE, uptake was significantly higher on the right side contralateral to the atresia. Hence, atresia during early development leads to plastic changes resulting in an interhemispheric imbalance of functional metabolism in favor of the auditory cortex contralateral to the manipulated ear. Distances between tone-induced 2-DG labeling in AI and AAF were increased in PAX, but smaller in ATR in the right compared to the left hemisphere, suggesting effects of atresia also on spatial relations in cortical tonotopic maps.

Regional cerebral palmitate incorporation after unilateral auditory deprivation in immature and adult Fischer-344 rats

Regional cerebral incorporation of intravenously injected [U- 14C]palmitate was measured from 1 day to 13 weeks after left cochlear destruction in 11-day- and 3 month-old, awake Fischer-344 rats. In 11-day-old animals, statistically significant left-right differences in incorporation were absent 1 day after cochlear destruction and were found only in parts of the cochlear nucleus and inferior colliculus after 1 week. After 6 to 13 weeks, consistent with functional neuroanatomy of central auditory regions, incorporation was reduced by 6 to 9% in the left cochlear nucleus and left lateral superior olivary nucleus, compared with corresponding right-side regions. The right medial superior olivary nucleus, medial nucleus of the trapezoid body, lateral lemniscus nucleus, inferior colliculus, medial geniculate body, and auditory cortex had 5 to 9% less incorporation than did corresponding left-side regions. Fewer significant differences after chronic auditory deprivation occurred in 3-month-old rats than in 11-day-old rats following cochlear destruction. Reduced incorporation corresponded to reported changes in cell morphology, which also were greater in immature than mature rats following auditory deprivation. The results suggest that the palmitate method can be used to identify long-term regional changes in the turnover of brain lipids after sensory deprivation.

Plasticity of binaural interaction. I. Effect of early auditory deprivation

Plasticity of binaural interaction. I. Effect of early auditory deprivation