The effect of aging on somatosensory evoked potentials following stimulation of the posterior tibial nerve in man.

Spinal- and scalp-recorded somatosensory evoked potentials following stimulation of the posterior tibial nerve were obtained in 20 normal young subjects, and 45 aged subjects who were classified into group A (61-74 years) and group B (75-88 years). The results may be summarized as follows: (1) Spinal potentials, N19 at the twelfth thoracic vertebra and N28 at the second cervical vertebra, were significantly prolonged in latency in aged subjects. The interpeak latency, N19-N28, which represents the conduction time through the spinal cord, was also prolonged in aged subjects. (2) The interpeak latencies, P28-N31 and P28-P35, which represent the conduction time from the medial lemniscus to the thalamus and to the sensory cortex, respectively, were prolonged in aged subjects, particularly in group B. (3) The interpeak latencies of cortical potentials following P35, which represent the intracortical transit times, did not show any significant difference between young and aged subjects. (4) Amplitudes of the spinal, and short- and middle-latency cortical potentials were smaller in the aged subjects than those of young subjects, particularly the far-field N31 potential at Cz' electrode. In contrast, the long-latency cortical potentials were larger in aged subjects, although not significantly so.