Stroke on both sides of brain
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Stroke Impact on Both Sides of the Brain: Insights from Recent Research
Introduction to Bilateral Stroke Effects
Strokes can have profound effects on both the affected and unaffected hemispheres of the brain. Understanding these impacts is crucial for developing effective rehabilitation strategies. This article synthesizes recent research on how strokes influence both sides of the brain, focusing on motor function, cortical reorganization, and cognitive outcomes.
Motor Function and Disinhibition in Both Hemispheres
Motor Disinhibition Post-Stroke
Research indicates that motor disinhibition occurs in both the affected and unaffected hemispheres shortly after a stroke. In a study involving patients with moderate to severe hemiparesis, significant reductions in intracortical inhibition (ICI) were observed in both hemispheres during the acute stage of recovery. Interestingly, patients who showed significant motor recovery exhibited a return to normal ICI in the unaffected hemisphere, while those with poor recovery continued to show disinhibition on both sides.
Bilateral Motor Training and Brain Activation
Bilateral upper limb training has been shown to enhance the interaction and balance between the motor hemispheres. A study using functional near-infrared spectroscopy (fNIRS) found that unilateral training significantly increased the coupling effect between the contralateral and ipsilateral motor cortices, promoting better brain reorganization and motor recovery.
Cortical Reorganization and Rehabilitation
Treatment-Induced Cortical Reorganization
Constraint-induced movement therapy (CIMT) has been demonstrated to induce significant cortical reorganization in stroke patients. Before treatment, the cortical representation area of the affected hand was smaller compared to the contralateral side. Post-treatment, this area enlarged, and motor performance improved significantly. Follow-up examinations showed that the cortical areas in both hemispheres became almost identical, indicating a return to normal excitability balance.
Interhemispheric Rivalry and Recovery
The concept of interhemispheric rivalry suggests that the non-lesioned hemisphere may inhibit the affected hemisphere, potentially impairing recovery. A case study reported that a patient with a right-sided hemiparesis due to a left-hemispheric stroke showed rapid improvement after a subsequent right-hemispheric stroke, supporting the idea that reducing interhemispheric inhibition can facilitate recovery.
Cognitive Decline and Brain Atrophy
Longitudinal Brain Changes and Cognitive Decline
Cognitive impairment is a common consequence of stroke, often associated with cortical and subcortical atrophy. Studies have shown that atrophy rates are higher in the ipsilesional hemisphere, particularly in the right hemisphere. Greater atrophy in the medial temporal lobe after left-sided strokes and larger stroke volumes after right-sided strokes are linked to cognitive decline over time.
Functional Differences Based on Stroke Laterality
Ipsilesional Hand Function
The ipsilesional hand, often considered the "good" side, can also exhibit deficits post-stroke. Research has shown that both hands of stroke patients, regardless of the lesion side, display segmented movements with multiple starts and stops, unlike the smooth movements of healthy controls. This suggests a global impairment in motor planning and execution. Additionally, individuals with left brain damage tend to perform better in dexterity tests compared to those with right brain damage, although maximum strength remains similar across groups.
Brain Activity During Micturition
Differences in brain activity during micturition have been observed between left- and right-sided strokes. Patients with right-sided strokes show markedly diminished brain activity in regions involved in lower urinary tract control, highlighting the functional disparities based on stroke laterality.
Conclusion
Strokes impact both hemispheres of the brain, affecting motor function, cortical reorganization, and cognitive outcomes. Rehabilitation strategies that consider these bilateral effects, such as bilateral training and addressing interhemispheric rivalry, can enhance recovery. Understanding the nuanced differences based on stroke laterality is essential for tailoring interventions to individual patients' needs.
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