Article
Physiological mapping of the human periventricular/periaqueductal gray matter using intraoperative microelectrode recordings and postoperative directional deep brain stimulation
Physiologische Exploration des periventrikulären und periaquäduktalen Graus mittels intraoperativer Mikroelektrodenableitungen und postoperativer direktionaler Tiefenhirnstimulation
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Published: | June 26, 2020 |
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Outline
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Objective: The periventricular and periaqueductal gray matter (PVG/PAG) is a common target in deep brain stimulation (DBS) surgery for intractable pain. Oculomotor side effects such as oscillopsia and gaze deviation are commonly reported in patients undergoing PVG/PAG-DBS. While the effects of electrical stimulation are relatively well described, the human midline mesodiencephalic transition zone is hitherto largely unexplored at a cellular level in man. Here, we describe both intraoperative and postoperative mapping results in the PVG/PAG region of a 51-year old patient suffering from intractable lower back and leg pain due to multiple failed back surgeries.
Methods: Microelectrode-recordings (MER) during awake stereotactic surgery provided unique close-up views of gaze-related neuronal activities. Directed electrical stimulation delivered through the implanted segmented DBS leads was then used during the postoperative phase to systematically explore stimulation-induced effects within the PVG/PAG region.
Results: Neuronal activity in the CM/Pf complex consisted of tonic regular single spike discharges intermingled with typical high-frequency burst discharges. At the ventral thalamic base, we noted the presence of neurons with tonic regular discharges at high frequency (70-100Hz). A decrease of background activity then indicated the transition to a fiber-rich area. On the right side, 4mm above the target level, the background became more active again. Here, we found several oculomotor responsive neurons over a course of 2mm on the central and posterolateral tracks, respectively. These neurons were silent at rest, and did not discharge upon upward or horizontal eye movements. All neurons became selectively active during downward movements of the eyes. During downward smooth pursuit, their discharge rate varied approximately with eye velocity. 3D-reconstruction revealed that the left lead tip was positioned within the PVG. The right lead tip, however, showed a depth deviation and was located slightly posterior within PAG.
Conclusion: Our case demonstrates that clinical assessment of ocular motility can be used intraoperatively to identify (pre-)motor centers for gaze in the human median rostral midbrain. Furthermore, the use of directional leads may prove especially helpful to further explore the intricate anatomical landscape of hitherto incompletely characterized brainstem DBS targets such as the PAG or the pedunculopontine nucleus.