A stroke happens when the blood supply to a particular area of the brain is interrupted, thus depriving neurons of oxygen. There are two ways this can occur: in a hemorrhagic stroke, a blood vessel bursts, spilling blood into the space around the brain cells, causing damage. In an ischemic stroke, blood ﬂow is interrupted but the blood vessel is undamaged. The deprived neurons suffer damage through deprivation of oxygen and nutrients, and this is reﬂected in whatever function the damaged brain region controlled.
Symptoms appear suddenly and often include numbness or weakness, usually affecting only one side of the body; some muscle paralysis on the same side; confusion; aphasia (trouble speaking or understanding speech); trouble seeing in one or both eyes; difﬁculty walking; loss of balance or coordination; and dizziness. The cell damage doesn’t kill the neurons immediately, however; treatment within several hours can often save them. In addition to the initial damage caused by the death of neurons, some of the brain damage that results from stroke appears to be a result of a toxic reaction to the primary damage. This reaction is poorly understood, but researchers are currently studying the mechanics of it and looking for ways to prevent this secondary injury, perhaps by developing drugs to protect the neurons from this damage.
Several other areas of research show promise for prevention of both strokes and the secondary damage that occurs after them. Vasodilators, substances that dilate blood vessels, thereby increasing the blood ﬂow to the brain, show some promise for improving the ﬂow of oxygen and nutrients to the affected area. Another interesting and unexpected area of promising research involves the study of hibernation processes. During hibernation, there is a very substantial decrease of blood ﬂow to the brain, so much so that it would result in brain death for a non-hibernating animal (or, by extension, a human). Much of the damage in stroke victims is caused by a far less dramatic decrease in blood ﬂow, so if researchers can work out how animals can hibernate without incurring serious brain damage, it may be possible to duplicate the processes involved to prevent neurological damage in stroke victims.
Another related phenomenon that may provide clues is hypothermia. People who have experienced hypothermia (dangerously reduced body temperature) have often gone without sufﬁcient oxygen for extended periods without serious brain damage. Understanding how this occurs may lead to new ways to handle the reduced blood ﬂow in strokes. Of course, the ideal treatment for stroke would be to discover a way to allow the brain to repair itself, since ordinarily, seriously damaged neurons are simply lost forever. Some evidence suggests that transcranial magnetic stimulation (TMS) may be that treatment.
In TMS, a rapidly changing magnetic ﬁeld is applied to the brain. A magnet by itself will have no effect on the brain at all. A pulsed magnetic ﬁeld, however, will induce any charged particles in its path (like the potassium and sodium ions in and around neurons, for example) to ﬂow, thus inducing an electric current. This has been experimented with as a treatment for depression, as well, as it is much more precise and easy to control than the electrical current used in electroconvulsive therapy (ECT). Results have been promising, especially since traditional ECT requires anesthesia and TMS does not. Some research with stroke victims suggests that TMS might possibly increase the brain’s ﬂexibility of function, thus speeding up recovery of functions after a stroke. Research on this treatment is still tentative, but quite promising.
Diagnosis of strokes is often accomplished through brief neurological examinations and blood tests, though CT and MRI scans and ultrasound have revolutionized the process. There are multiple known risk factors for stroke, including genetics (strokes seem to run in families), hypertension (high blood pressure), heart disease, diabetes, heavy alcohol consumption, high blood cholesterol levels, illicit drug use, and smoking. Additionally, pregnancy, childbirth, and menopause all elevate risk of stroke as well. None of these risk factors will inevitably lead to stroke, but prevention efforts have largely centered on getting people to reduce the risk by changing what they can from this list. Predicting who will have a stroke cannot be done with any certainty, but it may become possible, through the treatments described above, to greatly reduce the damage it causes in many cases (see also Brain Imaging Techniques).
- Delvaux, V., Alagona, G., and Gerard, P. “Post-Stroke Reorganization of Hand Motor Area: A 1-Year Prospective Follow-Up with Focal Transcranial Magnetic Stimulation.” Clinical Neurophysiology, 114(7) (2003): 1217–1225;
- Mills, K. R. Magnetic Stimulation of the Human Nervous System. New York: Oxford University Press, 2000.
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