Objective: Primary Lateral Sclerosis (PLS) is a clinical syndrome of progressive spasticity. Patients with PLS have slow voluntary movements. In PLS, degeneration of corticospinal tracts disrupts the communication between the motor cortex and motor neurons. Normally, voluntary movements are preceded by EEG waveform changes that begin before the movement occurs. These waveforms are called movement related cortical potentials (MRCPs). The first part of the MRCP represents neural activity in the motor cortex. The goal of this study is to determine whether the motor cortex and pre-motor cortex operate normally to generate these intrinsic signals for voluntary movement in patients with PLS.