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Think about the last time you walked down the street or grabbed a glass of water or spoke to a friend. How cool was that? It seems silly—reaching for a glass of water? Easy peasy—I’ve been doing that since age two, no applause needed.
We think it is simple enough, but in reality, our brains are working extremely hard to execute this movement, which includes calculating where exactly that glass of water is, how thirsty we are, how to lift our arms, move at a safe speed, open our hand to the correct diameter, and how to produce just enough grip to hold the glass steady without breaking it. How lucky many of us are to be able to do that smoothly and seemingly without thought.
For those who have experienced a brain injury, however, those movements become extremely difficult. Upwards of 75% of people who have suffered a stroke suffer long-term debilitating movement impairments. In fact, stroke is the leading cause of long-term disability in the United States.
Someone experiences a stroke when a blood vessel in the brain gets blocked or bursts. Essentially, it’s a heart attack in the brain. Blood vessels carry important nutrients, like oxygen and glucose (sugar), to neurons in the brain. So when a vessel gets blocked or ruptures, neurons in the area lose their source of blood, and they starve and die.
Depending on where in the brain the stroke occurred, the cells it affected may have been involved in different functions, such as helping a person read, move his or her left hand, see color, or decide which bread to buy. And so when those cells start to die, deficits in those areas start to develop. No stroke is the same, and so one person who has survived a stroke may not be able to walk, another person may not be able to talk in complete sentences or move her or his right arm, and another may not be able to see his or her left field of vision or understand music. While a stroke can happen anywhere in the brain, most people struggle with movement after a stroke because the blood vessel that serves areas of the brain controlling movement is extra vulnerable to blockage and bursting.
Since 1950, stroke survival rates have increased by 70%, mainly due to a greater understanding of how to prevent high blood pressure, advancements in the use of imaging to diagnose a stroke, and the FDA approval of a drug, tPA, that dissolves clots if it’s used within the first few hours after a stroke. A major focus of research now lies in how brains heal after a stroke, and how this healing sets the stage for a patient’s recovery.
Immediately after a stroke, the first step the brain takes to heal itself is to swell up. Similar to when you scrape your knee, your brain undergoes an inflammatory response as the immune system brings in the big guns to clear up the mess resulting from the blockage or rupture and contain the damage done. During this time, processing in the brain may slow down or even stop in the areas affected by the stroke. For this reason, a person’s arm or leg may be paralyzed right after a stroke, even though they may eventually regain some function.
The second step in the healing process involves neuroplasticity, which occurs in the days, weeks, and months following a stroke. Neuroplasticity means the brain is plastic, or able to change. So, rather than forever lose the function of the damaged area of the brain (e.g. the ability to talk, walk, decide), other areas of the brain take over to compensate. This process, however, often results in an insufficient recovery of function, as the new areas aren’t as equipped to carry out the function as well as the original, damaged areas.
You may have heard that the left side of your brain controls the right side of your body, because neurons in the motor areas of your brain cross over as they travel to the spinal cord. So, when a stroke damages the main motor area on one side of the brain, motor areas on the other side, as well as another motor area called the brainstem, can take over control for that side of the body. However, because these areas are not normally equipped to control complex movements on that side (the brainstem, for instance, usually controls things like posture), a person’s ability to move usually doesn’t fully recover. For example, a person who has suffered a stroke may not be able to move their joints independently and/or their limbs may become very stiff.
A major focus of research now lies in understanding how the brain changes after a stroke, how these changes lead to impairments, and how we can target those brain changes to help reverse those impairments. While we know the brain is changing, we still largely do not understand how it’s changing.
One approach is to recruit stroke patients for a study and analyze their brain activity while they move. When a volunteer wears an EEG cap, which looks like a swim cap with wires sticking out of it, researchers can measure brain activity in different areas of the brain—more activity in a certain area before or during movement signals that that area is used at that time, mainly to plan or execute the movement. Research at Northwestern University has shown that motor areas on the undamaged side of the brain (opposite to the stroke) work harder during movement. What this shows is that these undamaged areas are compensating for the other motor areas that were damaged by the stroke.
However, as expected, these movements that someone who has had a stroke performs using these compensating motor areas are impaired. Additional research has shown that using drugs that turn down activity in these compensating motor areas (e.g. the brainstem) actually improves someone’s ability to move after a stroke. This demonstrates that the areas that are trying to compensate for the damaged area of the brain may actually be causing more problems. This finding opens a door to a future therapeutic strategy.
Every second of every day, our brains are working hard to allow us to move, talk, see, laugh, and think, among so many other things, with ease. We often don’t consider how miraculous this is until a stroke makes these abilities extremely difficult or impossible to accomplish. While the brain has ways to heal itself after injury, sometimes it heals in non-optimal ways that lead to lifelong impairments. It’s extremely important to research strokes to uncover how to reverse and even prevent impairments. It’s a blessing to be able to read an article or walk down the street (or both at the same time!). Scientists are working to make it so people who have had a stroke can do these things again.
Jackie is a Ph.D. student in neuroscience at Northwestern University and is an Associate Editor of the Illinois Science Council Blog