Habituation: effects of regular and stochastic stimulation

The different effects of regular and stochastic stimulation on the flexor reflex of patients with the spinal cord totally divided and of normal subjects and on the blink reflex of normal subjects were studied.When the cutaneous stimulus was above but less than twice threshold, with regular stimulation habituation occurred; with stochastic stimulation, habitutaion either did not occur or it was minimal. Stochastic stimulation was at random stimulus intervals or with random stimulus intensities.When stimulus intensity was around threshold, habituation occurred with both kinds of stimulation, the response to stimulation soon ceasing to occur. When stimulus intensity was greater than twice threshold, habituation did not occur with both kinds of stimulation.When regular stimulation was given after the response had ceased to occur, extinction of the response beyond zero occurred.When a dishabituating stimulus was repeatedly applied in a regular manner, habituation to the dishabituating stimulus occurred.With regular and stochastic stimulation given as conditioning and test series, it was seen that stochastic stimulation caused, in addition to the short-term excitatory effect, the same long-term cumulative depressing effect on excitability as did regular stimulation.