INTRACRANIAL RECORDING FROM THE BRAIN-STEM AND THE TRIGEMINAL NERVE FOLLOWING UPPER LIP STIMULATION

Short latency evoked potentials following stimulation of the upper lip were recorded intracranially during neurosurgical procedures in 14 pa tients. In 10 patients, a suboccipital craniectomy provided direct acc ess to the trigeminal root and the pens at the root entry zone. Direct recordings from the trigeminal root were characterized by a large tri phasic potential at 2.4-2.7 msec. The latency of this potential increa sed as a result of moving the recording electrode proximally towards t he brain-stem. The same potential could be recorded from the brain-ste m surface at a latency suggesting an intra-axial presynaptic origin. A second component, N4.7, was recorded from over the most rostral aspec t of the brain-stem in 3 patients and from the tentorium free edge in 4 patients. This potential of smaller amplitude did not show significa nt difference in latency or polarity at various electrode locations, s uggesting a deep diencephalic origin remote from the recording electro de.