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Targeting the Pedunculopontine Nucleus: A New Neurophysiological Method Based on Somatosensory Evoked Potentials to Calculate the Distance of the Deep Brain Stimulation Lead From the Obex

Insola, Angelo MD*; Valeriani, Massimiliano MD, PhD§,¶; Mazzone, Paolo MD

doi: 10.1227/NEU.0b013e318249c726
Technique Assessment

BACKGROUND: Pedunculopontine tegmental nucleus (PPTg) deep brain stimulation (DBS) has been used in patients with Parkinson disease.

OBJECTIVE: To verify the position of the DBS lead within the pons during PPTg targeting.

METHODS: In 10 Parkinson disease patients undergoing electrode implantation in the PPTg, somatosensory evoked potentials were recorded after median nerve stimulation from the 4 DBS electrode contacts and from 2 scalp leads placed in the frontal and parietal regions.

RESULTS: The DBS electrode recorded a P16 potential (latency at contact 0, 16.33 ± 0.76 ms). There was a P16 latency shift of 0.18 ± 0.07 ms from contact 0 (lower) to contact 3 (upper). The scalp electrodes recorded the P14 far-field response (latency, 15.44 ± 0.63 ms) and the cortical N20 potential (latency, 21.58 ± 1.42 ms). The P16 potentials recorded by the intracranial electrode contacts are generated by the volley traveling along the medial lemniscus, whereas the scalp P14 potential represents a far-field response generated at the Obex level. Considering that the distance between the electrode contacts 0 and 3 is 6 mm, the distance of the electrode contact 0 from the Obex (ΔObex) was calculated by the equation: ΔObex = 6 × Δlatency P14- PPTg0/Δlatency PPTg0-PPTg3. The Obex-to-brainstem electrode distance obtained by the neurophysiological method confirmed that the electrode was located within the pons in all patients. Moreover, this distance was very similar to that issued from the individual brain magnetic resonance imaging.

CONCLUSION: Somatosensory evoked potentials may be a helpful tool for calculating the macroelectrode position within the pons during PPTg targeting.

ABBREVIATIONS: DBS, deep brain stimulation

DCN, dorsal column nuclei

IOMER, intraoperative microelectrode recording

PPTg, pedunculopontine tegmental nucleus

*Unità Operativa di Neurofisiopatologia, CTO, Rome, Italy

Unità Operativa di Neurochirurgia Funzionale e Stereotassica, CTO, Rome, Italy

§Divisione di Neurologia, Ospedale Pediatrico Bambino Gesù, IRCCS, Rome, Italy

Center for Sensory-Motor Interaction, Aalborg University, Aalborg, Denmark

Correspondence: Massimiliano Valeriani, MD, PhD, Divisione di Neurologia, Ospedale Pediatrico Bambino Gesù, IRCCS, Piazza Sant'Onofrio4, 00165 Rome, Italy. E-mail: and Angelo Insola, MD, Unità Operativa di Neurofisiopatologia, CTO, Via S. Nemesio 21, 00145 Rome, Italy. E-mail:

Received February 18, 2011

Accepted December 21, 2011

Copyright © by the Congress of Neurological Surgeons