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

Abstract

Knowledge that descending subthalamic influences act to determine responsiveness of the reticular formation (RF) to various sensory inputs has been confirmed and extended. Subthalamic lesions not only led to reduction of sciatic-evoked potentials in the RF but also decreased click- and flash-evoked potentials. Because RF-conducted evoked potentials were reduced following subthalamic lesion, it appears that subthalamic facilitatory influences are effective by virtue of their action on the basic excitability of RF neurons themselves and not as a result of alterations strictly of sensory input mechanisms. The distribution of these facilitatory influences to the RF is widespread; evoked potentials in the anterior and posterior midbrain RF were severely affected and those in the medullary RF were also reduced, though not as consistently as in the midbrain. It also appears that subthalamic lesions are capable of altering the later components of the primary sensory, cortical response to sciatic stimulation. Amphetamine was not capable of restoring the depressed reticular evoked potentials. Sequential lesions of the subthalamus revealed that the facilitatory influences are diffusely organized and not limited to any specific region of the subthalamus. Subsequent ventral thalamic lesions demonstrated the existence of inhibitory influences passing through areas dorsal to the subthalamus.