Cortico-motor excitability of the lower limb motor representation: a comparative study in Parkinson's disease and healthy controls

Objective: To compare indices of cortico-motor excitability derived from transcranial magnetic stimulation (TMS) of the lower limb motor representation in patients with Parkinson's diseases (PD) and healthy controls.Methods: The cortico-motor excitability of the lower limb motor area was studied both at rest (motor threshold, amplitude of motor evoked potentials (MEPs)) and during active contraction of the quadriceps (Quad) muscle (MEPs facilitation and silent period) in 10 PD patients (11 legs) and 11 healthy controls using single pulse TMS.Results: At rest, the motor threshold was found to be significantly lower and the amplitude of MEPs larger in patients than in controls. During active knee contraction, patients produced lower levels of MEP facilitation with respect to baseline values and the silent period was lengthened in comparison to controls.Conclusions: The present results provide further evidence from the lower limb motor area that enhanced cortico-spinal excitability is an important feature in the pathophysiology of PD.