Recovery cycles in the lemniscal system

Abstract

Recovery of the evoked response to controlled peripheral nerve stimulation was studied in the cat at the medial lemniscus, internal capsule, and somatosensory cortex with the following findings: 1. 1. In the unanesthetized, alert animal, recovery proceeds quickly with no evidence of facilitatory or inhibitory peaks at all recording locations. 2. 2. Barbiturate anesthesia prolongs the latter part of the relatively unresponsive period (RUP) in the lemniscus, increases the absolutely unresponsive period (AUP) and uncovers a period of increased responsiveness in the capsule, and increases both the AUP and RUP of the cortex with no evidence of subsequent periods of increased or decreased responsiveness. 3. 3. Mild hypothermia (31–32°C) in the absence of anesthesia prolonged the RUP in the lemniscus and both the AUP and RUP in the capsule and cortex. In the anesthetized animal, these changes were more marked and the period of heightened responsiveness in the capsule disappeared. While some evidence of increased responsiveness was seen in the cortex, recovery of this responsiveness was polonged. 4. 4. A stimulus placed near the end of the AUP of the capsule and cortical response, itself ineffective in producing a response, prolonged recovery of a subsequent test response.