Scalp recorded somatosensory evoked potentials to posterior tibial nerve stimulation in humans.

The somatosensory evoked potentials (SEPs) produced by stimulation of the right and left posterior tibial nerves individually and also by their simultaneous stimulation were recorded in 84 adult normal subjects up to 150 msec after the stimulus by electrodes placed on the cranial vertex and by rows of electrodes over the sagittal and coronal lines using references on the ear or in the nasopharynx. The statistical distribution of the latencies of their different peaks was established. The effect of simultaneous stimulation of right and left posterior tibial nerves on the early SEP components was described. Some details of the anatomy of the rolandic sulcus were inferred from the amplitude distribution of these potentials.

Elimination of EMG interference during recording of somatosensory evoked potentials elicited by posterior tibial nerve stimulation in patients with cervical spinal cord injury.

Recording SEPs to PTN stimulation in some patients with acute injuries of the cervical spine can be difficult due to the presence of involuntary activity of the neck and jaw muscles. The electrical potentials derived from this myogenic activity have a distribution along the sagittal line of the head which is uniform in amplitude while the amplitude of the SEPs recorded from points along this sagittal line is maximal over a point close to the vertex and less in front and behind this point. This fact has been utilized to devise a 'bipolar' derivation with one electrode on the vertex and two electrodes, one in front and one behind it on the sagittal line tied together as a reference. This effectively eliminates potentials of muscle origin from the SEP record. Other 'bipolar' combinations are not as effective in obtaining evoked potentials free of this muscle interference.