Vibratory stimulation. Part II. Vibratory stimulation as an evaluation tool

Phasic neural mechanisms are heavily involved in volitional movements, where as tonic mechanisms support postural adjustments. Yet, the two systems are so intimately related that any disturbance in one will exert profound effects on the other. Whether one system or the other is involved preferentially in different neural disorders is not known; hence, tests are needed to evaluate phasic and tonic functions independently. In this article, the classical applications of the tendon jerk reflex and H-response for assessing phasic mechanisms are first reviewed. Following this review, the tonic stretch reflex and tonic vibration reflex (TVR) are analyzed and compared. The effects of experimentally ablating or stimulating precise brain regions are described as a means of revealing the role of supraspinal mechanisms in the TVR. Finally, the responses to vibratory stimulation in specific motor disorders are examined and discussed as to their usefulness in prognosis and diagnosis.