Recovery from directional hypokinesia and bradykinesia in unilateral neglect

Abstract

Patients with acute right hemisphere (RH) damage and left unilateral neglect may exhibit slowness in both the initiation and execution of goal-directed movements toward the contralesional side (respectively, directional hypokinesia and directional bradykinesia). We retested 13 patients with RH damage, who on initial testing 1 year earlier had shown these impairments on a visually cued sequential movement task. Initiation and execution times were measured separately for leftward and rightward movement sequences, performed in either hemispace and across the body midline. Patients with anterior/subcortical lesions exhibited directional hypokinesia and bradykinesia on initial testing, but no longer showed either after 12 months. It is suggested that the recovery exhibited by these patients was determined conjointly by residual functioning of flexible anterior/subcortical structures involved in response production, in addition to the resolution of transient secondary dysfunction (i.e., diaschisis) of posterior (parietal) areas responsible for attentional orienting and target selection. In contrast, patients with posterior (parietal) lesions continued to exhibit directional hypokinesia after 12 months, probably as a result of permanent damage to a region whose dedicated or specialised functions cannot readily be compensated by other brain areas. These results support the notion that spatial attention and goal-directed movement are subserved by a distributed network involving separate but interconnected brain regions. Distinct functional losses may be predicted, in both the acute and chronic stages postinjury, on the basis of temporary or permanent dysfunction of discrete components of this network.