Effects of a Frontal Lesion on the Cortical Potentials Associated with Voluntary Movement in the Awake Monkey

An accidental, punctate lesion to a medial portion of the frontal lobe, including supplementary motor cortex and anterior commissure, produced a change in the cortical potentials preceding voluntary movement in a cynomolgus monkey. At the time of the lesion, the animal was highly trained in a repetitive voluntary movement task, and baseline mapping of specific movement-related potentials (MRPs) was complete. Prelesion MRPs were characterized by a well-defined N2 response, which began approximately 100 msec before the onset of movement. This response was centered over the contralateral precentral gyrus and believed to reflect the phasic portion of the corticospinal discharge. After the lesion, the animal fully recovered the ability to perform the movement task. However, the amplitude of N2 on the side ipsilateral to the lesion was significantly reduced. This decrease was not associated with any deficit in movement execution. EMG measurements did not exhibit any diminished or abnormal patterns of activity. These data suggest that portions of the frontal lobe not directly involved in the genesis of MRPs may still provide a supportive role in organizing the sequence and pattern of neuroelectric activity associated with movement. Furthermore, the findings document the sensitivity of MRPs for detecting subtle changes in the pattern of efferent electrical activity associated with a lesion within the brain, even in the absence of overt movement disorders.