Maturation Of Central Auditory Pathways Research Articles

Cortical auditory evoked potentials (P1 latency) in children with cochlear implants in relation to clinical language tests

Objective – To study the correlation between P1 latency and the results of clinical language tests (Reynell III and TROG-2), the latter were used as they are recommended for follow-up assessments of children with cochlear implants (Cis) by the Swedish National Quality Register for children with hearing impairment. Design – A clinical cohort study. Study sample – Cross-sectional and consecutive sampling of 49 children with CIs coming for clinical follow-up assessment from March 2017 – December 2019. Results – For all children tested, there was a significant negative correlation (Spearman’s rho= −0.403, p = 0.011) between hearing age and P1 latency. A significant correlation between P1 latency and the Reynell III result (Spearman’s rho = −0.810, p = 0.015) was found. In the TROG-2 group, there was no significant correlation between their P1 latency and their language test results (Spearman’s rho −0.239, p = 0.196). Conclusion – This method seems to be feasible and easily accepted. The study was conducted in a heterogeneous group of children that we meet daily in our clinic. The results indicated that P1 latency has a negative correlation with language development among our youngest patients fitted with CIs and might be a clinical tool to assess the maturation of central auditory pathways.

Neurodevelopmental Aspects and Cortical Auditory Maturation in Children with Cochlear Implants.

Background and objectives: The cochlear implant is not only meant to restore auditory function, but it also has a series of benefits on the psychomotor development and on the maturation of central auditory pathways. In this study, with the help of neuropsychological tests and cortical auditory potentials (CAEPs), we intend to identify a series of instruments that allow us to monitor children with a cochlear implant, and later on, to admit them into an individualized rehabilitation program. Materials and methods: This is a longitudinal study containing 17 subjects (6 boys and 11 girls) diagnosed with congenital sensorineural hearing loss. The average age for cochlear implantation in our cohort is 22 months old. Each child was tested before the cochlear implantation, tested again 3 months after the implant, and then 6 months after the implant. To test the general development, we used the Denver Developmental Screening Test (DDST II). CAEPs were recorded to assess the maturation of central auditory pathways. Results: The results showed there was progress in both general development and language development, with a significant statistical difference between the overall DQ (developmental quotient) and language DQ before the cochlear implantation and three and six months later, respectively. Similarly, CAEP measurements revealed a decrease of positive-going component (P1) latency after cochlear implantation. Conclusion: CAEPs and neuropsychological tests prove to be useful instruments for monitoring the progress in patients with cochlear implants during the rehabilitation process.

Central auditory development in children with hearing impairment: Clinical relevance of the P1 CAEP biomarker in children with multiple disabilities

Objective: We review the development and plasticity of the central auditory pathways in infants and children with hearing loss who are fitted with cochlear implants (CIs). Secondly, we describe case studies demonstrating the clinical utility of the P1 central auditory evoked potential (CAEP) for evaluating cortical auditory maturation in the rapidly increasing number of cochlear-implanted children who have multiple disabilities. Study design: Children who receive CIs provide a platform to examine the trajectories of deprivation-induced and experience-dependent plasticity in the central auditory system. We review the evidence for, and time-limits of, sensitive periods for cortical auditory maturation framing an optimal period for cochlear implantation. Finally, we evaluate the use of the P1 biomarker as an objective assessment tool in the special case of children with multiple disabilities. Results: The P1 response was useful in assessing central auditory maturation in patients with CHARGE association, ANSD, and Pallister-Killian syndrome concomitant with hearing loss. Conclusion: The presence of coexisting disabilities in addition to hearing loss poses unique challenges regarding both pre-intervention evaluation and post-intervention rehabilitation for children with multiple disabilities. When combined with a standard audiological test battery, the P1 CAEP biomarker has a useful role in objectively evaluating the maturation of central auditory pathways to determine the effectiveness of various intervention strategies in hearing-impaired children with multiple disabilities.

A Clinical Study of Cortical Auditory Evoked Potentials in Cochlear Implantees

Normal maturation of central auditory pathways is a precondition for the optimal development of speech and language skills in children. The temporal cortex gets acoustically tagged due to auditory stimulation and important changes occur in the higher auditory centers due to hearing loss of any type and degree. Cochlear implantation increases auditory sensitivity by direct electrical activation of auditory nerve fibers, enabling phonemic awareness, discrimination and identification ultimately yielding speech understanding. Early implantation stimulates a brain that has not been re-organized and will therefore be more receptive to auditory input and greater auditory capacity. Cortical potentials have enabled us to objectively study this phenomenon. To assess the outcomes of Cochlear implants on the auditory cortex by analyzing cortical auditory evoked potentials (CAEPs) in the habilitation period. This prospective clinical study was performed in 30 pre-lingual candidates with varied etiology of deafness who underwent cochlear implantation at our institute over the last 1year. The study group had two cohorts (group-1: 0-8years and group-2: 8-15years) which included candidates with normal inner ear and no syndromes or handicaps. All implantees in the study group underwent CAEP testing at 6months and 1year post-implantation and comparison of the CAEP wave parameters (P1 amplitude, P1 latency and P1 morphology) were done between the two cohorts. In children Implanted early (group-1) there was an early onset rapid increase in P1 amplitude along with a decrease in P1 latency during the follow-up period. Significant change in the CAEP wave morphology was also notable in group-1 unlike in group-2. Candidates who experienced less than 3years of auditory deprivation before implantation showed P1 latencies, which fell into the range of normal children within 6months of habilitation. Children with more than 6years of auditory deprivation, however, generally did not develop normal P1 latencies or morphology even after 1year of habilitation. The overall outcome with CAEP was much better in group-1 as compared to group-2 and the observations were is in comparison with the existing world literature. The advent of CAEP has objectively proved beyond doubt that there is a critical age for stimulating the auditory brain via cochlear implantation. There is considerable evidence for a developmental sensitive period, during which the auditory cortex is highly plastic. If sensory input is deprived to the auditory system during this sensitive period, then the central auditory system is susceptible to large scale reorganization. Restoring input to the auditory system by Cochlear Implant at an early age can provide the stimulation necessary to preserve the auditory pathways. However, if auditory input is not restored until after this developmental period, then the cross-modal reorganized pathways may exhibits abnormal functional characteristics as observed in recorded P1 amplitude, latencies and morphologies of CAEPs.

Central auditory development: Evidence from CAEP measurements in children fit with cochlear implants

In normal-hearing children the latency of the P1 component of the cortical evoked response to sound varies as a function of age and, thus, can be used as a biomarker for maturation of central auditory pathways. We assessed P1 latency in 245 congenitally deaf children fit with cochlear implants following various periods of auditory deprivation. If children experience less than 3.5 years of auditory deprivation before implantation, P1 latencies fall into the range of normal following 3–6 months of electrical stimulation. Children who experience greater than 7 years of deprivation, however, generally do not develop normal P1 latencies even after years of stimulation. Moreover, the waveforms for these patients can be markedly abnormal. Cortical reorganization stimulated by deprivation is likely to be a significant factor in both variation in the latency and morphology of the cortical evoked response to sound for children fit with a cochlear implant and variation in the development of oral speech and language function. Learning outcomes: The reader will be introduced to research using cortical evoked responses (CAEPs), positron emission tomography (PET) scans and in-depth recording from the auditory cortex of congenitally deaf cats that converges on the existence of a sensitive period for the development of central auditory pathways in children. The reader will also be provided with two case studies that illustrate the use of the P1 response as biomarker for development of central auditory pathways. Finally, suggestions for future research will be provided.

P1 Latency as a Biomarker for Central Auditory Development in Children with Hearing Impairment

We used the latency of the P1 cortical auditory-evoked potential (CAEP) as a biomarker for the development of central auditory pathways in three children who received intervention through hearing aids and/or cochlear implants. Our goal was to examine the clinical feasibility of using the latency of the P1 CAEP as an objective tool to evaluate whether acoustic amplification for hearing-impaired children has provided sufficient stimulation for normal development of central auditory pathways. If clinicians have such a marker, then they can more confidently make a decision about whether to provide a child with a cochlear implant following an appropriate hearing-aid trial. Using the same marker, clinicians will also be able to monitor the maturation of central auditory pathways once electrical stimulation is initiated.

Development of GABA, glycine, and their receptors in the auditory brainstem of gerbil: a light and electron microscopic study.

Inhibitory synaptic transmission is known to play an important role during the maturation of central auditory pathways. While there is a lot of information on the modulatory role of glycine (Gly) on the postsynaptic target nuclei in the developing auditory brain stem, such a role for gamma-aminobutyric acid (GABA) in the lateral superior olive (LSO) of neonatal gerbil has been only recently reported (Kotak and Sanes [1997] Soc Neurosci Abst 23:1549; Kotak et al. [1998] J Neurosci 18:4646-4655). Here we present further immunohistochemical findings and the first ultrastructural evidence documenting a significant decrease in the postsynaptic localization of the beta2,3 subunit of the GABA(A) receptor from postnatal day (P)4 to P14 in the LSO of gerbil and the shift in the location of most of the staining from dendritic to astroglial over the same time course. There was a concomitant increase in staining for the Gly receptor (GlyR) anchoring protein, gephyrin. At the same time, GABA and Gly did not show a significant change in their staining pattern, suggesting that the transmitter levels are not particularly indicative of the inhibitory function in the neonatal gerbil LSO, but their receptors on the postsynaptic cells are. The observations of the present study suggest that the early GABAergic inhibition may be important in establishing appropriate synaptic contacts in the LSO of gerbil.

Developmental changes in P1 and N1 central auditory responses elicited by consonant-vowel syllables

Normal maturation and functioning of the central auditory system affects the development of speech perception and oral language capabilities. This study examined maturation of central auditory pathways as reflected by age-related changes in the P1/N1 components of the auditory evoked potential (AEP). A synthesized consonant-vowel syllable (ba) was used to elicit cortical AEPs in 86 normal children ranging in age from 6 to 15 years and ten normal adults. Distinct age-related changes were observed in the morphology of the AEP waveform. The adult response consists of a prominent negativity (N1) at about 100 ms, preceded by a smaller P1 component at about 50 ms. In contrast, the child response is characterized by a large P1 response at about 100 ms. This wave decreases significantly in latency and amplitude up to about 20 years of age. In children, P1 is followed by a broad negativity at about 200 ms which we term N1b. Many subjects (especially older children) also show an earlier negativity (N1a). Both N1a and N1b latencies decrease significantly with age. Amplitudes of N1a and N1b do not show significant age-related changes. All children have the N1b; however, the frequency of occurrence of N1a increases with age. Data indicate that the child P1 develops systematically into the adult response; however, the relationship of N1a and N1b to the adult N1 is unclear. These results indicate that maturational changes in the central auditory system are complex and extend well into the second decade of life.