Rapid development of cortical auditory evoked potentials after early cochlear implantation Anu Sharma, CA Michael F. Dorman 1 and Anthony J. Spahr 1 Callier Advanced Hearing Research Center, University of Texas at Dallas,1966 Inwood Road, Dallas, TX 75235; 1 Arizona Biomedical Institute, Arizona State University, Tempe, AZ 85287-1908, USA CA Corresponding Author Received 22 March 2002; accepted 10 May 2002 The aim of our research was to estimate the time course of devel- opment and plasticity of the human central auditory pathways fol- lowing cochlear implantation. We recorded cortical auditory- evoked potentials in 3-year-old congenitally deaf children after they were ¢tted with cochlear implants. Immediately after implan- tation cortical response latencies resembled those of normal-hear- ing newborns. Over the next few months, the cortical evoked responses showed rapid changes in morphology and latency that resulted in age-appropriate latencies by 8 months after implanta- tion. Overall, the development of cortical response latencies for the implanted children was more rapid than for their normal- hearing age-matched peers. Our results demonstrate a high degree of central auditory system plasticity during early human de- velopment. NeuroReport13:1365^1368  c 2002 Lippincott Williams & Wilkins. Key words: Cochlear implant; Cortical auditory-evoked potentials; Plasticity INTRODUCTION The effects of congenital deafness on the human auditory pathways are not well understood. The effects are of sufficient magnitude that adults who have been deaf since birth receive essentially no speech understanding from electrical stimulation of the cochlea provided by a cochlear implant [1,2]. However, many congenitally deaf children, after receiving a cochlear implant, are able to acquire oral language [3,4]. The different outcomes occur, presumably, because degenerative changes take time to develop [5] and because young nervous systems exhibit a high degree of neural plasticity [6,7]. These findings suggest that the best time to implant a congenitally deaf child would be before the degenerative effects of sensory deprivation substantially alter the plasticity of the central auditory system. In humans, however, the time course of central auditory system plasticity is largely unknown. We are investigating the time course of development and plasticity of the central auditory system in congenitally deaf children following cochlear implantation. Our response measure is the latency of the P1 cortical auditory- evoked potential. The P1 response is generated by auditory thalamic and cortical sources [8–10]. P1 latency reflects the accumu- lated sum of delays in synaptic propagation through the peripheral and central auditory pathways [11]. Because P1 latency varies as a function of chronological age [12], P1 latency can be used to infer the development of auditory pathways in children fitted with an implant. In a previous study [13], we compared P1 latencies from 18 congenitally deaf children who were fitted with a cochlear implant by age 3.5 and from 18 age-matched normal-hearing peers. We found that the P1 latencies of implanted children after 6 months of implant use were not significantly different from their age-matched normal- hearing peers, suggesting that the functional development of central pathways was age-appropriate by 6 months after early implantation. We have since replicated this finding in a larger group of cochlear-implanted children [14]. In that study we examined the P1 latencies of 97 pre-lingually deaf children fitted with implants at ages ranging from 1.5 years to 17 years against the 95% confidence intervals of P1 latencies derived from 124 normal-hearing children ranging in age from 0.1 to 17 years. The results showed that children implanted under 3.5 years of age had age-appropriate P1 latencies after 6 months of implantation, while children implanted after age 7 had delayed P1 responses, sometimes even after years of implant use. Taken together, the results of these two studies suggest that there is a sensitive period of about 3.5 years during early development when cochlear implantation occurs into a relatively non-degenerate and/or highly plastic central auditory system. This view is supported by animal studies of deaf rats and congenitally deaf white cats fitted with cochlear implants who demonstrate the existence of a sensitive period for the development of auditory pathways [15–17]. Our finding of normal P1 latencies in children who had experienced about 3 years of auditory 0959-4965  c Lippincott Williams & Wilkins Vol 13 No 10 19 July 2002 1365 AUDITORYAND VESTIBULAR SYSTEMS NEUROREPORT