Changes in evoked potentials after experimental cervical spinal cord injury in the monkey

Abstract

Rhesus monkeys were subjected to acute cervical spinal cord trauma after chronic implantation of both cortical and deep electrodes. The method of injury was acute flexion-compression in the mid-cervical region. After stimulation of the sciatic nerve with a stimulus just above threshold at 10-sec intervals for 1 msec, evoked potentials were recorded from the contralateral sensory cortex, ventral posterior lateral nucleus of the thalamus, internal capsule, and the brain stem reticular formation. The evoked potential was still present immediately after injury, but starting at approximately 20–90 sec after the injury it began to disappear rapidly. Thereafter, the primary evoked response could not be demonstrated until it began to reappear about 24 hr after the injury; however, no averaged evoked response was ever obtained from the brain stem reticular formation, even after 6 days. The loss of the evoked response is thought to coincide with the onset of primary hemorrhage and edema, demonstrated in the cord. A synchronous 16-cycle spindle activity, which seems to be time-locked to the stimulus and not present in any control recording, began to appear about 30 min after the injury and became more prominent in ensuing days. This 16-cycle activity, characteristic of fast sleep spindles, coupled with the loss of the evoked response in the brain stem reticular formation may account for the transient loss of consciousness that occurs in the monkeys after the cervical injury, and for the persistent alteration of the conscious level we have noted.