Corticoreticulospinal control of the tonic vibration reflex in the cat

The cortico-reticulospinal system has been investigated using vibration to produce a tonic reflex in an intact cat. Stimulation of the motor cortex potentiated the effects of medial medullary inhibition but not the facilitation evoked from the lateral medulla.The cortico-bulboreticular pathways were found to project bilaterally to the medulla. Medullary stimulation produced bilateral facilitation or inhibition of the tonic vibration reflex (TVR). Although the cortico-bulboreticular pathway projected bilaterally the effect evoked from the motor cortex was clearly contralateral in its end result. The cortico-reticulospinal system usually inhibits the tonic vibration reflex of both triceps surae and tibialis anterior, but on occasions inhibition of triceps surae was accompanied by a phasic contraction of the tibialis anterior. Stimulation of the contralateral caudate nucleus failed to influence the TVR directly or the response evoked by medullary stimulation. Stimulation of the contralateral red nucleus evoked a facilitation of the TVR which continued several seconds after red nucleus stimulation ceased.It was concluded that those medullary neurones which inhibit tone in flexor and extensor hind limb muscles of the cat are controlled directly by the motor cortex and are uninfluenced by caudate nucleus or red nucleus. The facilitatory neurones in the lateral medulla appear to be independent of cortical control.