Neurophysiological effects of -X impact acceleration.

In 19 experiments, eight unanesthetized Rhesus monkeys, with torsos restrained in a seated position, and with head and neck free to move, were subjected to peak sled accelerations in the -X direction ranging from 42 m/s2 to 963 m/s2. Recordings of cortical somatosensory evoked potentials were made using recording electrodes chronically implanted over the somatosensory cortex. Electrical pulse stimuli were delivered at a rate of 5 Hz through spinal electrodes located at L1-L2. Evoked potentials were recorded prior to impact, through the impact event, and subsequent to impact, then subjected to quantitative analysis procedures which included normalized cross-correlation and exponential regression. The results of this analysis suggest a neurophysiological effect which holds promise as an indicator of a pre-injurious central nervous system condition. This effect is a transient increase of 2% to 5% in the latency of the primary surface positive peak of the cortical evoked potential. There appears to be a threshold for these increases in latency at peak sled accelerations in the region of 600 m/s2. This is consistent with previous findings and provides the basis for applying these techniques to human volunteer experiments.