Hemispatial and directional performance biases in motor neglect

Motivationally responsive motor deficits may occur in isolation or as part of more general neglect syndromes. We describe three patients with two discrete syndromes of isolated motor neglect, differentiated primarily by their performance in motor tasks enacted within or toward the contralesional hemispace. The lesions in our patients likely disrupted attentional interactions with two separable sensorimotor processing subsystems. Physiologic data support the existence of a parietal-lateral premotor circuit that processes information encoded in spatial coordinates referenced to the extrapersonal environment and of a basal ganglionic-mesial premotor circuit that processes information mostly encoded in egocentric skeletomotor coordinates. The correlation of ischemic lesions resulting in hemispatial and directional biases in motor neglect with disruption of known physiologic subsystems may provide the basis for rational cognitive rehabilitation of these higher-order motor deficits. These observations are supported by recent PET studies that document the presence of specific attentional-motoric interactions within discrete processing components of a distributed sensorimotor attentional network.