The effect of darkness on knee-jerk reflexes

In considering the processes that regulate motor functions in darkness, the following factors should be taken into account: the fear of losing spatial orientation, daily processes in the circadian system, stimulating influence of the light, and a mechanism that induces anxiety, probably of rudimentary origin, serving as a sentinel center monitoring the probable aggressiveness of the environment, which increases in the dark. The results of published studies suggest that the anxiety response to darkness induces emotional stress, and, consequently, an increase in the background supraspinal excitatory influence mediated by the corticospinal tract and leading to decreased α-motoneuron thresholds.