Shorter Latencies of Components of Middle Latency Auditory Evoked Potentials in Congenitally Blind Compared to Normal Sighted Subjects

Abstract

A previous study which reported shorter latencies of the Nb component of AEP-MLRs in congenitally blind compared to normal sighted subjects, formed the basis for the present study. The blind subjects had received a rehabilitation program from the age of 4 years onwards, which may have influenced auditory function. Hence the present study was designed to compare the AEP MLRs of normal sighted subjects with age-matched blind subjects who had not undergone early rehabilitation. Auditory evoked potentials (0 to 100ms. range) were recorded in 10 congenitally blind subjects (average age = 22.4 ± 4.9 yrs.) and an equal number of age-matched subjects with normal vision. There were two repetitions per subject. The peak latencies of both the Pa (maximum positive peak between Na and 35 ms.) and Nb (maximum negative peak between 38 and 52 ms.) waves was significantly shorter in congenitally blind compared to normal sighted subjects. Since the Pa and Nb waves are believed to be generated by the superior temporal cortex (Heschl's gyrus), it appears that processing at this neural level occurs more efficiently in tie blind. Also, in spite of the absence of an early rehabilitation program the present subjects showed the same auditory changes as those reported earlier.

Key Words:

• Middle latency auditory evoked potentials
• congenitally blind
• normal-sighted
• primary auditory area
• auditory inputs for rehabilitation