The saccade-related local field potentials of the superior colliculus: a functional marker for localizing the periventricular and periaqueductal gray.

This study was intended to investigate the neural signals related to oculomotor and visual activity during horizontal saccades in humans and to explore the potential of using such signals as a functional marker for localizing the periventricular and periaqueductal gray. We recorded the local field potentials (LFPs) via implanted electrodes in the rostrolateral part of the periventricular and periaqueductal gray in four patients (six electrodes) who underwent deep brain stimulation for treatment of neuropathic pain. The functional composition of the saccade-related LFPs under different visual conditions was characterized using time-frequency analysis, and it was correlated with the anatomic placement of the electrodes on the postoperative magnetic resonance images. The magnitude of oculomotor signals varied predictably with the proximity of the recording electrode to the superior colliculus; the oculomotor activity was represented specifically in the alpha (8-13 Hz) and theta (4-8 Hz) bands for saccades and in the alpha band for fixation, whereas the visual activity was represented in the delta band (1-3 Hz) of the LFPs. The compound LFP signals of the superior colliculus embrace the synchronized population activity of multimodalities, which can be differentiated in the frequency domain. This is the first time LFP signals of the human superior colliculus have been characterized. Such signals may be used as a functional marker for electrode placement in the periventricular and periaqueductal gray for modulation of pain.