Enhanced Effective Connectivity Between Primary Motor Cortex and Intraparietal Sulcus in Well-Recovered Stroke Patients

Abstract

Background and Purpose-Ischemic strokes with motor deficits lead to widespread changes in neural activity and interregional coupling between primary and secondary motor areas. Compared with frontal circuits, the knowledge is still limited to what extent parietal cortices and their interactions with frontal motor areas undergo plastic changes and might contribute to residual motor functioning after stroke. Methods-Fifteen well-recovered patients were evaluated 3 months after stroke by means of functional magnetic resonance imaging while performing visually guided hand grips with their paretic hand. Dynamic causal modeling was used to investigate task-related effective connectivity between ipsilesional posterior parietal regions along the intraparietal sulcus and frontal key motor areas, such as the primary motor cortex, the ventral premotor cortex, and the supplementary motor area. Results-Compared with healthy controls of similar age and sex, we observed significantly enhanced reciprocal facilitatory connectivity between the primary motor cortex and the anterior intraparietal sulcus of the ipsilesional hemisphere. Beyond that and as a fingerprint of excellent recovery, the coupling pattern of the parietofrontal network was near-normal. An association between coupling parameters and clinical scores was not detected. Conclusions-The

Low‐Frequency Brain Oscillations Track Motor Recovery in Human Stroke

“…We analyzed time–frequency dynamics at 1 to 10Hz around onset of a whole‐hand grip (see Fig A) in a group of healthy participants (n = 19), age‐matched to the patient cohort. A selection of contralateral frontal (supplementary motor area [SMA], ventral premotor [PMv], primary motor cortex [M1]) and parietal (anterior intraparietal sulcus [aIPS]) motor areas were chosen based on peak of activation by the same grip task in a previous functional MRI experiment . Premovement activity was most strongly modulated at 3 to 5Hz, with a significant amplitude increase about 600 milliseconds prior to the grip onset for a duration of about 600 milliseconds.…”

“…Third, source activity between close targets is hard to unambiguously separate. Although advanced spatial reconstruction methods can separate activity from aIPS and M1, and this study benefits from previously identified individual motor coordinates in an overlapping patient and control population using the same motor task, we cannot claim spatial accuracy at those targets.…”

“…We found that movement‐related LFOs in the stroke‐lesioned hemisphere gradually increased with time after stroke, presumably as a result of biological repair mechanisms involving plasticity. Lesion‐induced plasticity in the human brain has been demonstrated in the form of a reorganization of task‐specific networks, for example, the parietofrontal dorsolateral and dorsomedial network . To date, integrity of the corticospinal tract, a lateralized activation pattern in motor cortical regions, M1–M1 interhemispheric connectivity, and the strength of the beta rebound, among others, are known factors determining the degree of recovery of motor function in human stroke patients.…”

The functional role of beta‐oscillations in the supplementary motor area during reaching and grasping after stroke: A question of structural damage to the corticospinal tract

“…Within this framework especially the ventral and dorsal premotor cortex, the SMA and the parietal areas might play a relevant role (Grefkes et al, ; Schulz, Park, et al, ). Parietal areas demonstrate stronger connectivity with the motor cortex during hand movements in chronic stroke patients (Pool et al, ; Schulz et al, ; Bönstrup et al ). Causal evidence for this assumption comes from TMS deactivation studies, where inhibition of PMd (contralesional and ipsilesional), as well as the parietal lobes and contralesional M1 led to decreased motor performance (e.g., Bestmann et al, ; Fridman et al, ; Johansen‐Berg et al, ).…”

“…To resolve time‐frequency dynamics in source space, we reconstructed activity at pre‐defined coordinates of interest (COI) using spatial filtering. Coordinates for M1, PMv, and SMA were derived from a previous functional Magnetic Resonance Imaging (fMRI) experiment involving a hand grip task in healthy elderly participants (Schulz et al, ). All lesions were flipped to the left side in order to allow a comparison of contralateral and ipsilateral activations across patients.…”