CEREBRAL POTENTIALS-EVOKED BY RECTAL DISTENSION IN HUMANS

The afferent pathways from the rectum can be stimulated and studied af ter mechanical distention of the rectum. We studied the rectum-brain a xis in 24 healthy young adults. The rectum was stimulated with a recta l balloon using inflation volumes of 10 ml and 30 ml air at a stimulat ion frequency of 0.167 Hz. Additional studies were carried out with 20 ml distention volumes, random stimulation frequency, and stimulation rates of 0.08 Hz and 0.017 Hz. We found two different cortical EPs. An early onset EP was present in 21 of the 24 subjects. P1 latency short ened significantly with increasing distention volumes, but peak amplit udes did not change significantly with larger distention volumes. A la te onset EP was present in all subjects with NI latency of 210+/-15 ms ec, PI latency of 316+/-24 msec, and NII latency of 444+/-34 msec. The different EPs could be due to stimulation of two different visceral a fferent pathways which are present in the same individual, due to stim ulation of two different fiber populations or due to simultaneous stim ulation of afferents in surrounding structures. EP recording after rec tal stimulation might be useful in future studies of patients with abn ormal rectal sensation.