Movement disorders : official journal of the Movement Disorder Society
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Repetitive transcranial magnetic stimulation (rTMS) delivered at 5 Hz frequency and suprathreshold (RMT) intensity produces a progressive facilitation of motor-evoked potential (MEP) amplitude that outlasts the end of stimulation. This phenomenon is related to a short-term enhancement of cortical excitatory interneurones. In this study, we investigated whether 5 Hz-rTMS elicits similar MEP facilitation during stimulation and similar facilitatory after-effects in patients with upper limb dystonia and healthy subjects. ⋯ MEP amplitudes during and after 1 Hz-rTMS remained unchanged. Ulnar nerve stimulation did not change the test MEP amplitude. We conclude that in patients with upper limb dystonia there is an abnormal recovery from MEP facilitation after suprathreshold 5 Hz-rTMS suggesting an abnormal pattern of short-term cortical plasticity.
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Patients with Parkinson's disease (PD) have difficulty performing tasks relying on inhibitory control and working memory, functions of the prefrontal cortex. Eye movement paradigms can be used to investigate basic sensorimotor functions and higher order cognitive aspects of motor control. This study investigated inhibitory control and spatial working memory in the saccadic system of 13 individuals with mild-moderate PD and 13 age-matched controls. ⋯ Results for the PD group indicated an increased percentage of response selection errors during an oddball task, reduced suppression of inappropriate reflexive saccades during memory-guided tasks (but not during fixation or saccade-engagement tasks), and an increased percentage of express and anticipatory saccades. Spatial working memory was preserved in the PD group during single and two-step memory-guided tasks. These findings are consistent with dysfunction within fronto-striatal and prefrontal-collicular pathways influencing suppression and selection of eye movements.