Effect of different stimulus frequencies on short-latency somatosensory-evoked potentials in patients with focal brain lesions.
To investigate whether the abnormality of short-latency somatosensory evoked potentials(SSEPs)in patients with focal brain lesions is enhanced by different stimulus frequencies, the median nerve at the wrist in 10 normal subjects and 12 patients with cortical (frontal, central and parietal) lesions was stimulated electrically at 1.3-18.3 Hz. Normal subjects had decreased frontal P22-N30 and parietal P27 amplitudes at high (12.3 and 18.3 Hz) stimulus frequencies, whereas the N20 amplitude was relatively preserved. Dissociated loss of frontal P22-N30 occurred in patients with frontal lesions, but the preserved parietal components had characteristics similar to those of the non-affected side or of normal subjects at the various stimulus rates, which is evidence of an independent pathway for forming the frontal components. A N20 amplitude decrease occurred at high stimulus rates in the patients with central lesions, probably because of disturbed synaptic transmission. A paradoxical amplitude increase occurred at the high stimulus rates in patients with parietal lesions, which is indicative of inhibitory function loss in the sensory cortex or thalamo-cortical networks. In conclusion, change in the stimulus frequency is a useful method for detecting sensory process alteration in patients with focal cortical lesions.
Department of Neurosurgery, School of Medicine, University of Occupational and Environmental Health, Yahatanishi-ku, Kitakyushu 807-8555, Japan.
Tetsuya
T
Gennmoto
Eiichirou
E
Urasaki
Akira
A
Yokota
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001927:Brain Diseases / Q000175:diagnosis* / Q000503:physiopathology; D002540:Cerebral Cortex; D004558:Electric Stimulation; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology; D008875:Middle Aged; D011930:Reaction Time