Low temperature stimulation augments early wave component of somatosensory evoked response in humans and Macaca...

An early wave component of the scalp-recorded SER increases in amplitude when cold and electrical stimulation are combined. This change is accompanied by subjective reports of perceptual change in the intensity, domain or painfulness of the electrical stimulus in humans. Further results suggest that observation of the augmentation is dependent on normal functioning of both large and small peripheral fiber populations. This augmentation is also observed in Macaca mulatta monkeys. Under the same conditions, the spinal segmental SER is observed to obtain a new wave. This wave is time-locked to the electrical stimulus and has a latency longer than the earliest, but shorter than the latest traditional slow waves. The interaction of the cold and electrical stimuli to produce the cortical augmentation suggests the existence of a facilitatory mechanism. The level at which this operates and the mechanism through which it functions are discussed. The relationship of this augmentation to arousal phenomena is also examined.