DIFFERENCES BETWEEN CONGENITALLY BLIND AND NORMALLY SIGHTED SUBJECTS IN THE P1 COMPONENT OF MIDDLE LATENCY AUDITORY EVOKED POTENTIALS1
R. Nagarathna, H. R. Nagendra, Shirley Telles and K. V. Naveen.
Vivekananda Kendra Yoga Research Foundation
R. Srinivas, K. S. Nirmala
Department of Neurology, Ramaiah Medical College, &Teaching Hospital
Summary: Auditory evoked potentials (0 to 100 msec. range) were recorded two times for 9 congenitally blind children (age= 14.1 yr. ± 1.4 yr.) and 9 age-matched children with normal vision. The groups peak latency and amplitude of the P1 wave were compared. The peak latency was significantly lower for the congenitally blind than for the normally sighted on a two-factor analysis of variance. Since the P1 wave is thought to correspond to either the ascending, reticular activating system or the primary auditory cortex, these results suggest that information processing at these neural levels may occur more efficiently in the blind.
Congenitally blind subjects were reported by Strelow and Brabyn (1982) to show sensitivity in auditory perception, enabling them to use echoes to perceive spatial positions of objects. This interesting result has a neurophysiological basis. The long latency event related potential waves (NI, P2, and P3) showed shorter latencies and larger amplitudes in early blind humans than those with normal vision (Niemeyer & Starlinger, 1981). The Na and Pa components of middle latency auditory evoked potentials were not significantly different in congenitally blind subjects and those with normal vision (Naveen, Srinivas, Nirmala, Nagendra, & Telles, 1997); however, the Nb component (average peak latency 44.3 msec.) had a significantly shorter latency in congenitally blind persons. This suggested that auditory information processing at the level of the posteromedial part of the primary auditory cortex, the known generator of the Nb wave (Liegeois-Chauvel, Musolino, Badier, Marquis, & Chauvel, 1994) was more efficient in the blind.
The present report presents the analysis of the P1 wave in the congenitally blind and subjects with normal vision described above (Naveen, et al. 1997).