Stroke and Neuroplasticity

Author: Mirella Magalhães Tenório Brito & Nicodemos Teles de Pontes Filho, MDPosted on: Sunday 02 October 2005

Stroke is the most common neurological disease that affects the nervous system and it is also the principal cause of mental and physical disabilities. It happens due to an interruption in the blood stream to the brain, this interruption can happen like an obstruction of the artery that supplies the brain - the so-called ischemic stroke, or by the rupture of a vessel-the Hemorrhagic stroke.

The most important causes related to stroke are: high blood pressure, diabetes mellitus, heart diseases, fat, sedentariness and smoking.

The consequences depend on: the location, the affected brain area’s size, and the time passed from its occurrence until the patient assistance (the quicker the recovery starts, the better is the prognosis). The most common sequels are hemiplegia and visual, speaking and memory alterations.

The Brain’s Blood Supply

The blood reaches the brain through the vertebral artery and the internal carotid artery. Both arteries communicate each other through the Circle of Willis. This is an arterial anastomosis that provides blood supply to the brain’s hemispheres, and the anterior cerebral arteries, the posterior cerebral arteries, the anterior artery communicants, the posterior arteries communicants and the internal carotid form it. These arteries have very thin walls, which makes them more vulnerable to hemorrhages. The cerebral artery most affected by a stroke is the middle cerebral artery.

Lesions and Neural Plasticity

The brain damage caused by a stroke may result in the loss of cerebral function. However, the brain can use a process called “neuroplasticity” to adjust itself functionally, by reorganizing the cortical maps, which contributes to the stroke recovery. The changes in the cortex organization include an increase in the number and density of dendrites, synapses and neurotrophic factors (these are essentials for the survival of nervous cells). After damage has been afflicted to the motor cortex, changes of activation in other motor areas are observed. These changes can occur in homologue areas of the non-affected hemisphere (which can substitute for the lost functions) or in the intact cortex adjacent to the damage. Thanks to these cortical reorganizations, which begins from one to two days after the stroke, and can be extended for months, the patients can recover, at least in part the lost abilities.

The recovery of functions of the limbs, which is promoted by plasticity, is more difficult to occur, due to a phenomenon known as “learned non use“. With the loss of a brain area’s function, the body part that was linked to this area is also affected and its mobility power is lost too. As the patient cannot move his most affected limb, he compensates this using the other limb. Thus, after a certain period, when the damage effects aren’t present anymore and brain readaptations happen, the movements could be recovered, but the patient has already learned that the limb is no longer functional.

Treating Inactivity

In the period following the stroke, a decrease in the extension of the cortical representation areas is noticed for the affected muscles: because they are not in use (aren't working regularly), its correspondent area in the brain is not stimulated. In a effort to decrease or to recover from the “learned nonuse” effects, one of the practices that have been used is the Constraint-Induced Movement Therapy (CI-therapy) or forced use, which increases the plastics changes that are favorable to the patient’s recovery.

This technique consists in the forced use of the affected arm by the limited use of the non-affected arm. During a 10 to 15 days period, the patient’s non-affected arm is immobilized. Consequently, the affected arm, stimulating the damaged cortex, can only do many activities like dressing, eating, writing, cooking, etc.. In this period, the patient has a six daily hours of physiotherapy training, doing repetitive tasks with the affected arm. Due to this increased use of the affected arm, the brain area connected to it is stimulated once again and occurs an intense cortical reorganization. This reorganization increases the representation area of this limb in the cortex and the motor function ability is improved. So the CI-therapy can be considered remarkably effective against the” learned” nonuse.

Conclusions We finish by concluding that neuroplasticity is essential to the stroke patient’s recovery, and that one of the methods used to stimulate it is the CI-therapy, which have been achieving important results in the motor cortex reorganization and in getting over the learned non-use.

References Cramer, S. C., Moore, C. I., Finklestein, S. P., Rosen, B. R. (2000). A Pilot Study of Somatotopic Mapping after cortical infarct. Stroke 31:668-671

Liepert, J., Bauder, H., Miltner, W. H. R., Taub, E., Weiller, C. (2000). Treatment-Induced Cortical Reorganization After Stroke in Humans. Stroke 31: 1210-1216

Liepert, J., Miltner, W.H.R., Bauder, H., Sommer, M., Dettmers, C., Taub, E., Weiller, C. (1998). Motor cortex plasticity during constraint-induced movement therapy in stroke patients. Neurosci Lett. 250:5–8.

Taub ,E., Uswatte, G., Pidikiti, R.D. (1999). Constraint-induced movement therapy. a new family of techniques with broad application to physical rehabilitation-a clinical review. J Rehab Res Dev. 36: 237–251.