Temporal integration shown in the late component of the human blink reflex

Abstract

The effect of closely spaced stimulus pairs (S1–S2), one at or above threshold for eliciting the second electromyographic burst of the cutaneous blink reflex (R2) and one below threshold intensity, on the latency, duration, and area of R2 was examined in four experiments. The size of the R2 elicited by a threshold S1 (but not by an S1 at three times threshold intensity) was augmented by threshold or near-threshold S2s that appeared after stimulus onset asynchronies of 4, 8, and 16 msec. More intense S2s had a greater effect on R2 size and led also to a slight shortening of R2 latency. Although R2 augmentation was accompanied by a modest increase in response duration, this increase in duration was by itself insufficient to account for the augmentation of response amplitude. Subreflexogenic S1s (at 0.1, 0.2, 0.4, and 0.8 times R2 threshold intensity) did not affect the R2 elicited by an S2 at threshold intensity or two times threshold intensity. Unlike the simple brainstem pathway which mediates R1, the more complex brainstem pathway which mediates R2 is capable of summing stimulus energy over time.