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Inhibition of the contralesional dorsal premotor cortex to enhance motor function of the affected hand after stroke with 1 Hz rTMS
Since several years novel electrophysiological treatment strategies such as transcranial magnetic stimulation (rTMS) are under exploration in motor rehabilitation after stroke. Nowak D A et al., 2009. After stroke, enhanced activity and excitability within motor areas of the contralesional hemisphere for movements of the affected hand is a frequent finding. Murase N et al., 2004. Functional MRI studies showed a negative correlation between the degree of task-related activation in several regions of the contralesional hemisphere and the outcome in subacute stroke patients. Nowak D A, Grefkes C, Fink G R, 2008; Ward N S et al., 2003. Within the concept of interhemispheric competition enhanced inhibition from contralesional M1 is supposed to hamper motor processing and recovery of motor function within the ipsilesional motor network. Nowak D A et al., 2009. Murase N et al., 2004. Several independent proof-of principle studies have shown that inhibition of contralesional M1 by means of 1 Hz rTMS significantly reduces enhanced neural activity within motor areas of the contralesional hemisphere and at the same time improves motor function of the affected hand after stroke. Murase N et al., 2004. In humans neural connectivity between dorsal premotor cortex (PMd) and the primary motor cortex (M1) within one hemisphere is dense and most relevant for the control of hand movements. Chouinard PA, Paus T, 2006. Inhibition of PMd by 1 Hz rTMS causes a long-lasting reduction of excitability in ipsilateral M1. Assuming the concept of interhemispheric competition after stroke it appears reasonable to ask if 1 Hz rTMS over contralesional PMd produces a comparable enhancement of motor function of the affected hand after stroke as observed for 1 Hz rTMS over contralesional M1. In our study we tested if, compared to healthy control subjects, 1 Hz rTMS over the contralesional PMd influences cortico-spinal excitability (motor evoked potentials,
MEP size), long- lasting cortical inhibition of contralesional M1 (cortical silent period, CSP duration), interhemsipheric inhibition from the contralesional M1 towards the ipsilesional M1 (ipsilateral silent period, ISP duration), and motor function of the affected hand after stroke (Jebsen Taylor test, JTT).
Material and Methods:
We studied 15 healthy subjects with right hand preference and 14 patients with right hand preference with sensimotor impairment of one hand after first left or right middle artery (MCA) stroke. Patients and healthy controls received inhibitory (1Hz) rTMS over the left (healthy subjects) or contralesional PMd (patients) with 15 minutes stimulation, 900 pulses and 110% of the resting motor threshold. For stimulation we used a 70 –mm figure-of-eight coil and a Magstim Super Rapid stimulator (Magstim Company, Dyfed, UK). To test for changes in cortico-spinal excitability motor evoked potentials (MEP), cortical silent period (CSP) were obtained from the unaffectetd/ right hand. The ipsilateral silent period (ISP) was assessed from the affected left hand. For behavioral testing, each participant performed the Jebsen Taylor Test of hand function for both hands. All tests were performed prior to and after the intervention.
Results and Interpretation:
1 Hz rTMS over the dorsal premotor cortex caused a significant reduction in cortico-spinal excitability of the contralesional/left primary motor cortex and increased long-lasting intracortical inhibition of the contralesional/left primary motor cortex, both in patients and healthy controls. Interhemispheric inhibition from the left/ contralesional to the right/ipsilesional primary motor cortex was not significantly influenced by premotor rTMS both in healthy subjects and stroke patients. The function for the affected hand in stroke patients improved in the JTT whereas healthy subjects showed no changes in motor function.