A Sensitive Period for the Development of the Central Auditory System in Children with Cochlear Implants: Implications for Age of Implantation

Abstract

Our data suggest that in the absence of normal stimulation there is a sensitive period of about 3.5 yr during which the human central auditory system remains maximally plastic. Plasticity remains in some, but not all children until approximately age 7. After age 7, plasticity is greatly reduced. These data may be relevant to the issue of when best to place a cochlear implant in a congenitally deaf child.

Altered Cortical Activity in Prelingually Deafened Cochlear Implant Users Following Long Periods of Auditory Deprivation

“…The group of Sharma (Sharma et al 2002;Dorman et al 2007) who reports a lack of N1 used a different stimulus, a 90-ms speech segment acoustically delivered to the CI processor, than studies reporting an N1 (Gordon et al 2008;Jiwani et al 2013; current study) who used a short train of pulses presented through a single electrode or a pair of electrodes. However, Ponton and Eggermont (2001) reporting a lack of N1 also used a short pulse train.…”

“…Pulse trains were generated using the Cochlear Custom Sound EP 3.1 software and presented at a rate of 0.9 Hz at the individual's maximum comfortable loudness level (C-level). These settings of stimulation rate and level are very similar to settings in the CI literature (Ponton and Eggermont 2001;Sharma et al 2002;Gordon et al 2008;Jiwani et al 2013). For all participants, phase widths of the biphasic pulses were set at 25 μs and interphase gaps at 8 μs.…”

“…Since the emergence of the N1 peak coincides with the development of complex auditory skills in children, it is suggested that these pathways play an important role in the processing of sounds in complex conditions such as speech in noise (Ponton et al 2000;Eggermont and Ponton 2003). In prelingually deaf children, who have been fitted with a cochlear implant early in life, the maturation of the predominant positive P1 peak follows the normal pattern as seen in normal hearing children (Sharma et al 2002;Dorman et al 2007). In such children, a normal N1 may develop after the long use of the CI (Jiwani et al 2013).…”

“…In such children, a normal N1 may develop after the long use of the CI (Jiwani et al 2013). After long durations of deafness (96 years), there are signs that the maturation of the more superficial layers of the auditory cortex becomes impaired, resulting in the absent development of the N1 and the predominance of the positive peak in these prelingually deaf and late implanted children (age at implantation 96.5 years) (Sharma et al 2002;Dorman et al 2007). Also, shorter periods of deafness (~3 years) during early childhood (3.5-6.5 years of age) may block N1 development (Ponton and Eggermont 2001).…”

“…Studies in prelingually deaf children who received a cochlear implant after several years of auditory deprivation and beyond the supposed sensitive period of 3.5 years revealed that the N1 peak did not develop and only an aberrant P1 peak was present (Ponton and Eggermont 2001;Sharma et al 2002;Dorman et al 2007;Kral and Sharma 2012). This lack of N1 might reflect corticocortical deficits within the superficial supragranular layers caused by long-term auditory deprivation.…”