Pain-related somatosensory evoked potentials

lThe authors reviewed basic and clinical reports of pain-related somatosens ory evoked potentials (SSEP) after high-intensity electrical stimulation [p ain SSEP(E)] and painful laser stimulation [pain SSEP(L)]. The conduction v elocity of peripheral nerves for both pain SSEP(E) and pain SSEP(L) is appr oximately 10 to 15 m/second, in a range of A6 fibers. The generator sources are considered to be the secondary somatosensory cortex and insula, and th e limbic system, including the cingulate cortex, amygdala, or hippocampus o f the bilateral hemispheres. The latencies and amplitudes are clearly affec ted by vigilance, attention-distraction, and various kinds of stimulation a pplied simultaneously with pain. Abnormalities of pain SSEP(L) reflect an i mpairment of pain-temperature sensation, probably relating to dysfunction o f A delta fibers of the peripheral nerve and spinothalamic tract. In contra st, conventional SSEP after nonpainful electrical stimulation reflects an i mpairment of tactile, vibratory, and deep sensation, probably relating to d ysfunction of A alpha or A beta fibers of the peripheral nerve and dorsal c olumn. Therefore, combining the study of pain SSEP(L) and conventional SSEP is useful to detect physiologic abnormalities, and sometimes subclinical a bnormalities, of patients with peripheral and central nervous system lesion s.