Introduction Studies of sensory deprivation in non-human mammals have demonstrated important features of brain maturation that may be relevant to auditory development in profoundly deaf children. Without sensory input, subcortical and cortical neurons fail to develop normal adult response properties. In the guinea-pig, for example, an appropriate mapping of auditory space on neurons in the external nucleus of the inferior colliculus does not develop without audi- tory experience. 1 In the kitten, the development of normal cortical ocular dominance columns requires patterned visual stimulation. 2 Studies of sensory deprivation have also demonstrated that once stimu- lation is restored, considerable recovery of function may occur. For example, when kittens reared in complete darkness from birth are returned to a normal visual environment, there is an initial period of behavioral blindness. If the period of dark-rearing is restricted to the first 6 months of life, visual acuity then gradually increases to normal or near-normal levels with a rate of change similar to that observed for kittens raised in a normal visual environment. 3 Thus, the visual system of dark-reared kittens retains considerable plasticity despite delays imposed by the period of sensory deprivation. For profoundly deaf children, auditory depriva- tion adversely affects the development of language and communication skills. The extent to which these abilities are disrupted or delayed depends on a number of factors, including the age of onset and duration of deafness. 4 For these individuals, at least some aspects of auditory sensation can be restored by electrical stimulation of auditory nerve fibers through a cochlear implant. By examining these chil- dren, it may be possible to determine whether matu- ration progresses in those areas of the brain that are deprived of their sensory input. It may also be possible to determine the extent to which the human auditory system retains its plasticity, thus allowing the re-introduction of sensory stimulation to restore the maturational sequence. Maturation of auditory cortical function may be assessed behaviorally, but these measures place demands on non-auditory functions such as attention and memory. 5,6 Consequently, behavioral measures also reflect immaturities in neural systems that govern these functions. On the other hand, electrophysiolog- ical recordings such as evoked responses can provide a direct and objective measure of maturational changes in auditory nervous system activity. 7 Activity in the evoked response represents synchronous neural activation produced by stimulus onset. 8 Maturational changes that result in increased conduction velocity and faster synaptic transmission are reflected in age- related decreases in evoked response latency. 9 As a measure of auditory system maturation, the latency of a robust component in the cortical audi- tory evoked response, the positive peak P 1 , was assessed in normal-hearing and implanted children and adults. Time courses of the cortical maturation Auditory and Vestibular Systems, Lateral Line 1 1 1 1 1 p © Rapid Science Publishers Vol 8 No 1 20 December 1996 61 DEAF children fitted with a cochlear implant provide a unique opportunity to examine the effects of auditory deprivation on the maturation of the human auditory system. We compared cortical evoked potentials recorded in implanted and normal-hearing children and found that age-dependent latency changes for the P 1 compo- nent, fitted to a decaying exponential curve, showed the same rate of maturation. For implanted children, however, maturational delays for P 1 latency approxi- mated the period of auditory deprivation prior to implantation. This indicates the auditory system does not mature without stimulation. Nonetheless, the audi- tory system retains its plasticity during the period of deafness since the re-introduction of stimulation by the cochlear implant resumes the normal maturational sequence. Key words: Auditory maturation; Cortical evoked poten- tials; Deprivation; Human; Plasticity Auditory system plasticity in children after long periods of complete deafness Curtis W. Ponton, CA M anuel Don, Jos J. Eggermont, 1 M ichael D. Waring, Betty Kwong and Ann Masuda Electrophysiology Department, House Ear Institute, 2100 West 3rd Street, 5th Floor, Los Angeles, CA 90057, USA; 1 Department of Psychology, University of Calgary, Calgary, Canada CA Corresponding Author NeuroReport 8, 61–65 (1996)