Low and high-frequency somatosensory evoked potentials recorded from the human pedunculopontine nucleus

To investigate the generators of the somatosensory evoked potential (SEP) components recorded from the Pedunculopontine Tegmental nucleus (PPTg).

Twenty-two patients, suffering from Parkinson's disease (PD), underwent electrode implantation in the PPTg area for deep brain stimulation (DBS). SEPs were recorded from the DBS electrode contacts to median nerve stimulation.

SEPs recorded from the PPTg electrode contacts could be classified in 3 types, according to their waveforms. (1) The biphasic potential showed a positive peak (P16) whose latency (16.05 ± 0.61 ms) shifted of 0.18 ± 0.07 ms from the lower to the upper contact of the electrode. (2) The triphasic potential showed an initial positive peak (P15) whose latency (15.4 ± 0.2 ms) did not change across the DBS electrode contacts. (3) In the last SEP configuration (mixed biphasic and triphasic waveform), the positive peak was bifid including both the P15 and P16 potentials.

While the P16 potential is probably generated by the somatosensory volley travelling along the medial lemniscus, the P15 response represents a far-field potential probably generated at the cuneate nucleus level.

Our results show the physiological meaning of the somatosensory responses recorded from the PPTg nucleus area.