Spasticity is a disorder characterized by increase in velocity-related muscle tone as a part of upper motor neuron syndrome. Although the mechanisms underlying stroke-related spasticity have not been fully understood, the current view is that spasticity is related to an imbalance between descending excitatory and inhibitory systems that regulate spinal stretch reflex and associated with abnormal intraspinal processes. The reticulospinal pathway (RSP) is at the center of this mechanism called cortical disinhibition. The dorsal RSP, which has an inhibitory effect on the spinal stretch reflex, originates from the medullary reticular formation and is under cortical control. In contrast to dorsal RSP, medial RSP which is not under the control of motor cortex originates from pontine reticular formation,and has an excitatory effect on spinal stretch reflex. The main motor cortex region controlling unilateral dorsal RSP is the premotor cortex. Unilateral RSP indirectly synapses with motor neurons via interneurons in the ventromedial intermediate zone in both halves of the spinal cord, and directly synapses with motor neurons of proximal extremity muscles. That is, a single limb is represented in both premotor cortices. This suggests theoretically that if the corticoreticular pathway controlling dorsal RSP is modulated by dorsal premotor cortex stimulation, there may be a change in the regulation of the intraspinal network regulating the stretch reflex. Furthermore, in stroke patients with severe motor impairment, the relationship between high cortical centers and the primary motor cortex is more in the form of facilitation rather than interhemispheric inhibition between the primary motor cortices. In other words, stimulation of one side premotor cortex may affect motor impairment and spasticity by affecting primary and high motor cortical centers of both hemispheres and both halves of the spinal cord. Therefore, the hypothesis in this study is that the application of repetitive transcranial magnetic stimulation (rTMS) over the contralesional dorsal premotor cortex in chronic stroke patients changes the severity of spasticity. Based on this hypothesis, our aim is to investigate the effect of rTMS over the contralesional dorsal premotor cortex on the severity of spasticity in patients with chronic stroke with moderate to severe upper extremity spasticity.
The reticulospinal pathway (RSP) is at the center of spasticity mechanism. The RSP indirectly synapses with motor neurons via interneurons in the ventromedial intermediate zone in both halves of the spinal cord, and directly synapses with motor neurons of proximal extremity muscles. The main motor cortex region controlling unilateral RSP is the premotor cortex. That is, a single limb is represented in both premotor cortices. This suggests theoretically that if the corticoreticular pathway controlling RSP is modulated by dorsal premotor cortex stimulation, there may be a change in the regulation of the intraspinal network regulating the stretch reflex. Therefore, the hypothesis in this study is that the application of repetitive transcranial magnetic stimulation (rTMS) over the contralesional dorsal premotor cortex in chronic stroke patients changes the severity of spasticity.