Handgrip-Related Activation in the Primary Motor Cortex Relates to Underlying Neuronal Metabolism After Stroke

Abstract

Background. Abnormal task-related activation in primary motor cortices (M1) has been consistently found in functional imaging studies of subcortical stroke. Whether the abnormal activations are associated with neuronal alterations in the same or homologous area is not known. Objective. Our goal was to establish the relationships between M1 measures of motor-task-related activation and a neuronal marker, N-acetylaspartate (NAA), in patients with severe to mild hemiparesis. Methods. A total of 18 survivors of an ischemic subcortical stroke (confirmed on T2-weighted images) at more than six months post-onset and 16 age- and sex-matched right-handed healthy controls underwent functional MRI during a handgrip task (impaired hand in patients, dominant hand in controls) and proton magnetic resonance spectroscopy (1H-MRS) imaging. Spatial extent and magnitude of blood oxygen level–dependent response (or activation) and NAA levels were measured in each M1. Relationships between activation and NAA were determined. Results. Compared with controls, patients had a greater extent of contralesional (ipsilateral to impaired hand, P < .001) activation and a higher magnitude of activation and lower NAA in both ipsilesional (P = .008 and P < .001, respectively) and contralesional (P < .0001, P < .05) M1. There were significant negative correlations between extent of activation and NAA in each M1 (P = .02) and a trend between contralesional activation and ipsilesional NAA (P = .08) in patients but not in controls. Conclusions. Our results suggest that after stroke greater neuronal recruitment could be a compensatory response to lower neuronal metabolism. Thus, dual-modality imaging may be a powerful tool for providing complementary probes of post-stroke brain reorganization.