Effects of subthalamic stimulation on sensory-evoked potentials in the reticular formation and cortex

Abstract

Stimulation of the subthalamic region of the diencephalon was used to study the dynamic nature of descending influences, previously shown to be important in determining the responsiveness of the brain-stem reticular formation to various sensory inputs. All results were obtained in acute experiments using bipolar stimulating and recording electrodes. Experiments involved interaction of subthalamic stimulation with sciatic, click or flash stimulation. Though there were some cases of increases in sensory-evoked potentials, in general, subthalamic stimulation led to blocking of the evoked potentials. Tetanization, bursts and single subthalamic stimuli were effective, in that order. Sciatic-evoked potentials were reduced or abolished, and click- and flash-evoked potentials were also decreased significantly though the blocking interactions were not as great as for sciatic-evoked potentials. Subthalamic interaction effects were widespread in the brain-stem reticular formation and cortex. Sciaticevoked potentials in the midbrain were affected more than in the medullary reticular formation, and those in association cortex were more severely reduced than in the sensorimotor cortex. Progressive, vertical penetrations indicated that the blocking interaction effects were not restricted to any well-defined fiber tract or small region of the subthalamus or midbrain reticular formation. In general, significant blocking interaction was obtained at intervals from 50 to 400 msec, though it was best at the shorter intervals.