Cortical connectivity after subcortical stroke assessed with functional magnetic resonance imaging

Abstract

Objective: This study aimed at identifying the impact of subcortical stroke on the interaction of cortical motor areas within and across hemispheres during the generation of voluntary hand movements. Methods: Twelve subacute stroke patients with a subcortical ischemic lesion and 12 age-matched control subjects were scanned using 3-Tesla functional magnetic resonance imaging. Subjects performed visually paced hand movements with their left, right, or both hands. Changes of effective connectivity among a bilateral network of core motor regions comprising M1, lateral premotor cortex, and the supplementary motor area (SMA) were assessed using dynamic causal modeling. Results: The data showed significant disturbances in the effective connectivity of motor areas in the patients group: Independently from hand movements, the intrinsic neural coupling between ipsilesional SMA and M1, and the interhemispheric coupling of both SMAs was significantly reduced. Furthermore, movements of the stroke-affected hand showed additional inhibitory influences from contralesional to ipsilesional M1 that correlated with the degree of motor impairment. For bimanual movements, interhemispheric communication between ipsilesional SMA and contralesional M1 was significantly reduced, which also correlated with impaired bimanual performance. Interpretation: The motor deficit of patients with a single subcortical lesion is associated with pathological interhemispheric interactions among key motor areas. The data suggest that a dysfunction between ipsilesional and contralesional M1, and between ipsilesional SMA and contralesional M1 underlies hand motor disability after stroke. Assessing effective connectivity by means of functional magnetic resonance imaging and dynamic causal modeling might be used in the future for the evaluation of interventions promoting recovery of function.

The second face of blindness: Processing speed deficits in the intact visual field after pre- and post-chiasmatic lesions

“…Alterations in down-stream, higher cortical areas, not directly affected by the lesion, were already demonstrated by gene expression studies [42] and single-unit recordings in animal models [43,44], as well as MEG [45] and fMRI studies in humans [20,[46][47][48][49][50][51][52]. This is in line with findings from motor [53,54] and attentional systems [55] where lesion-induced network modifications have been increasingly recognized and appreciated. However, the behavioral correlates of network alterations are still poorly understood in all systems.…”

State-Dependent and Timing-Dependent Bidirectional Associative Plasticity in the Human SMA-M1 Network

“…We demonstrate state-dependent and timing-dependent, topographically specific bidirectional Hebbian-like associative plasticity in the SMA-M1 network. Recent studies showed a significant role of effective coupling of neuronal activity in the SMA-M1 network for motor outcome in patients after stroke (Grefkes et al, 2008(Grefkes et al, , 2010. In this context, the present study may signify therapeutic potential to support purposeful modification of coupling in the SMA-M1 network in neurological disorders in which dysfunction of this network contributes to the clinical impairment.…”

Asymmetric control mechanisms of bimanual coordination: An application of directed connectivity analysis to kinematic and functional MRI data

“…The dynamic causal modeling (DCM) is a hypothesis-driven approach, which was specifically designed to evaluate the intrinsic and task-dependent influences that a particular brain area exerts over the activity of another area (Friston, 2003;Stephan et al, 2004;Grefkes et al, 2008). The DCM treats the brain as a deterministic system, in which external input causes changes in neural activity that, in turn, lead to changes in the fMRI signal.…”