Somatosensory evoked response (SER) was studied in 70 patients with neurosurgical disorders and 20 nomal, healthy men, in order to find out whether SER is helpful as a diagnostic aid for neurological ...diseases. Electric stimulations were given to the tibial nerve to provoke monosynaptic reflex of the M. soleus. The strength ranges of electric stimulations were classified as follows： (1) The weak range; H-wave of the monosynaptic reflex can be seen alone. (2) The medium range; both of H- and M-wave are appeared. (3) The strong range; H-wave is decreased in amplitude, or M-wave can be seen alone. SERs were led from the scalp electrodes placed at the vertex (Cz), left (C^3 ) and right (C^4 ) parietal regions by means of the averaging computer (ATAC-501). In the normal subjects, the response appeared to have a least 8 distinct peaks, beginning with a small triphasic wave (ABC) with the latency of 37, 57 and 75 msec, respectively, followed by a negative peak (D) with that of 110 msec and subsequent positive-negative sequences (E, 195- F, 251; G, 300; and H, 400). Although there were some inter-individual variations, each component of the normal SERs could be classified in two groups of ABC as the primary response and D-H as the secondary response.
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