Role of the Contralesional vs. Ipsilesional Hemisphere in Stroke Recovery

Abstract

Following a stroke, the resulting lesion creates contralateral motor impairment and an interhemispheric imbalance involving hyperexcitability of the contralesional hemisphere. Neuronal reorganization may occur on both the ipsilesional and contralesional hemispheres during recovery to regain motor functionality and therefore bilateral activation for the hemiparetic side is often observed. Although ipsilesional hemispheric reorganization is traditionally thought to be most important for successful recovery, definitive conclusions into the role and importance of the contralesional motor cortex remain under debate. Through examining recent research in functional neuroimaging investigating motor cortex changes post-stroke, as well as brain-computer interface (BCI) and transcranial magnetic stimulation (TMS) therapies, this review attempts to clarify the contributions of each hemisphere toward recovery. Several functional magnetic resonance imaging studies suggest that continuation of contralesional hemisphere hyperexcitability correlates with lesser recovery, however a subset of well-recovered patients demonstrate contralesional motor activity and show decreased functional capability when the contralesional hemisphere is inhibited. BCI therapy may beneficially activate either the contralesional or ipsilesional hemisphere, depending on the study design, for chronic stroke patients who are otherwise at a functional plateau. Repetitive TMS used to excite the ipsilesional motor cortex or inhibit the contralesional hemisphere has shown promise in enhancing stroke patients' recovery.

Functional near-infrared-spectroscopy-based measurement of changes in cortical activity in macaques during post-infarct recovery of manual dexterity

“…Our current results, in which activation was enhanced more in the ipsilesional PMv of the monkey with less damage (Monkey 1) and in the contralesional PMv of the monkey with more damage (Monkey 2), are also consistent with data from stroke patients and brain-damaged animals. Previous studies have indicated that functional reorganization of the motor cortex may occur in both the ipsilesional and contralesional hemispheres during functional recovery after stroke, and that the contralesional motor cortex may play a greater role in recovery when damage is more severe, because neuronal reorganization for functional recovery within www.nature.com/scientificreports www.nature.com/scientificreports/ the ipsilesional side may be difficult to accomplish under these circumstances [3][4][5][6]11,13,15,16,28 . In our previous PET study using M1-lesioned monkeys, enhanced activation was found in the ipsilesional PMv 21 ; by 2 months after lesioning, the success rate of precision grip in the M1-lesioned monkeys had recovered to within the 95% confidence level for performance before the injection.…”

Morphometric MRI findings challenge the concept of the “unaffected” hemisphere in Rasmussen encephalitis

“…Rudebeck and colleagues recently discovered a progressive cortical gray matter (GM) decline in the unaffected hemisphere that was even more pronounced than in the affected hemisphere of patients with chronic, early stage RE . This is surprising as the contralesional hemisphere is thought to be unaffected by the pathologic process and might compensate for losses of the ipsilesional hemisphere . However, the scant number of imaging studies with RE patients has investigated either the acute‐stage (≤2 years after disease onset, according to previous studies) or the chronic, early stage (>2 years after disease onset) of RE in childhood, and therefore, little is known about the later trajectory of the disease.…”

“…the pathologic process and might compensate for losses of the ipsilesional hemisphere. 7 However, the scant number of imaging studies with RE patients has investigated either the acute-stage (≤2 years after disease onset, according to previous studies 8,9 ) or the chronic, early stage (>2 years after disease onset) of RE in childhood, and therefore, little is known about the later trajectory of the disease. It was our objective to assess the GM volume differences and changes in patients with chronic, late-stage RE, using an optimized VBM protocol in both cross-sectional and longitudinal study designs.…”

White Matter Degeneration after Ischemic Stroke: A Longitudinal Diffusion Tensor Imaging Study

“…We did observe contralesional changes in diffusivity in V1, M1, the PMC, and the superior temporal gyrus. Contralesional DTI changes in the motor cortex after stroke have been observed in human and animal studies 23,24 and correlate with functional motor outcome. 25 All patients in this study with a deficit on the motor leg item at baseline recovered by 1 month after stroke, and therefore these changes may reflect neurological recovery.…”