Post-stimulation effects of high-frequency stimulation on sensory discharge from muscle.

Previously the application of stimuli of 600 Hz at adjustable strength applied to a muscle's nerve has been proposed as a means of reducing the muscle's contraction in spastic conditions, or when combined with a second tetanic stimulation, of limiting contraction to smaller, physiologically more relevant motor units in the paralyzed state. The side-effects on muscle spindles of such stimuli as seen in the cat's gastrocnemius are reported. During stimulation axonal impulses followed faithfully for periods running into minutes. After stimulation, a pause in ongoing firing with a duration dependent on stimulus-train length and a two-phased recovery occurred. Responses to dynamic stretch of the muscle were affected as well. The contractions of intrafusal fibers activated in several ways was seen to strongly offset the depression. In a clinical application, nevertheless, short-lived depression of all proprioceptive modalities following stimulation should be expected, with corresponding disturbance on sensory perception and reflex effects.