The effect of experimental concussion on somatosensory evoked potentials

Cortical somatosensory evoked potentials (SEPs) were recorded following experimental acceleration concussion in the rat. Immediately after head injury there was a general reduction in the amplitude of the SEP, and all its components were either temporarily abolished or increased in latency. The early components of the SEP recovered much more rapidly than did the amplitude and latencies of the later potentials. The purpose of the study was to investigate the relative effects of concussion on the lemniscal system (whose activity is reflected by the discrete early components of the SEP) and the reticular activating system (whose activity is reflected by the diffuse high amplitude late component of the SEP). Contrary to a widely accepted theory, there was a delay in transmission of somatosensory information through the lemniscal pathways as well as through the reticular system following head injury. Such an observation is consistent with recent studies of SEPs recorded from humans comatose after head trauma. As the changes in the morphology of the waveform of the SEP following concussion can be simulated by simply recording evoked potentials at high rates of stimulation, this suggests that the delays are caused by a failure or malfunction of synaptic transmission, but the level at which this is occurring remains to be determined.