The cells that keep your brain functioning are nothing like the ones on your skin, shedding and renewing itself with each turn of the moon. Once a brain cell or a neuron dies, your body cannot replace it with another. Instead, it turns into a scar. A ghost of a cell when you look at it through a microscope. Unfortunately, there are many things that can damage or kill off this finite resource.
Stroke is one of them. This disease comes in two flavors where one can suffocate your neurons. Like a man choking on a piece of fruit, this kind of stroke is defined by a blockage-- depriving your cells of much needed oxygen. The other type of stroke comes from a ruptured blood vessel, the cells drowning all the toxins that should have stayed inside the piping. The last two decades have seen an increase in the absolute incidence of stroke, in the years of life lost to disability, and in the mortality rates of this disease.
But is that the end for someone who has suffered a stroke? Do we just pack up and resign ourselves to the reality of scarred tissue and disability?
The short answer is no. Rehabilitation after stroke is the standard of care to help people regain function. But how does one regain function when neurons cannot regenerate?
The magic (read: science) lies in something called neuroplasticity.
See, brain cells or neurons look a bit like trees. They have branches that extend outwards, like arms reaching for the heavens to receive sunlight. They have a long trunk that ends in a bundle of roots. And as with a tree, a single neuron can create a maze of branches and its roots can reach deep into the soil. Through these branches and roots, a neuron can connect to another-- whispering messages that fly faster than the blink of an eye.
Neuroplasticity is the ability of your neurons, often spurned by a certain stimulus, to reorganize its structure and reach out its many branches to form new connections. Neurons can grow like plants hungry for the sunlight, crawling as far as they can reach. And when connections are strengthened and exercised, this can compensate for the death of other neurons.
But our neurons are not in a constant state of “plasticity”. There are specific drivers of plasticity such as a person’s age. These are specific times called “critical periods” in a normal child’s development where the brain is more plastic and more eager to learn things about the world--- and learn them very quickly. Other drivers of plasticity include traumatic brain injuries, and stroke.[4,7]
Now, if the brain is plastic after a stroke and neurons can reorganize, why is stroke still a leading cause of disability worldwide?
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Truth be told, the mechanisms of neuroplasticity are still shrouded by mystery. Scientists and researchers can make educated guesses on how it works in people by looking at how it works in mice. They can watch the branches of the neurons grow, and record the details (the when, and the where, and the what makes it go faster) of these findings. But at the end of the day, we are not mice--- the mechanism and period of maximal neuroplasticity remains unknown in humans.
But wherever there is an unknown, research continues.
In stroke patients, it has been established that rehabilitation helps regain function. That is, the affected body part will be molded, under the guidance of physical therapists, to help a person function better. What researchers are discussing now are the devilish details--- when should we start this rehabilitation? What kind of exercises would benefit the patients? How long should these exercises be?
AVERT (A Very Early Rehabilitation Trial for Stroke) was a trial that sought to answer some of those questions. It enrolled more than 2000 patients across more than 50 stroke units in 5 different countries. “Very early” specifically meant starting exercises within 24 hours of the stroke event. Sadly, the researchers have found that patients who underwent rehabilitation within a day of the stroke did not fare better than those who waited for a few days.
Instead, they found that when they started mattered less than the schedule of the sessions themselves. Patients who had shorter (not more than 10 minutes a session) but more frequent sessions fared better after 3 months. Each additional session increased the odds of a good outcome by as much as 13% with some patients having more than 10 sessions of 10 minutes each daily-- depending on how much they can handle.
Other trials have compared the different kinds of exercises that target the different body parts that are affected by stroke. For stroke that affects the legs, they weren’t able to find any particular rehabilitation exercise that did better than others. But when it came to stroke that affected the arms, patients who underwent modified constraint-induced movement therapy (mCIMT) seemed to have better initial results than those who didn’t. This is a kind of therapy that forces a patient to use and exercise their less abled arm-- when this remains unexercised, it could atrophy, become spastic, and be even harder to use in the future. Although, the researchers did recommend a bigger study to be more confident in the results.
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Stroke doesn’t only affect limbs. It can also affect the way someone speaks. This inability to speak or understand words properly after a stroke is termed “aphasia”. Sadly, some research has shown that one hour daily exercises on speech was not more effective than undergoing no treatment for aphasia. Thus, researches like this pose even more questions on the limits of neuroplasticity in stroke. Is the mechanism by which motor neurons branch out different from those related to speech?
The brain and its cells are infinitely interesting-- able to contemplate its own existence and to ask questions about its own workings. Though the answers do not reveal themselves to us readily, there is wonder in how our brains reorganize themselves around an injury to help us function better.
- Illis, L. Central nervous system regeneration does not occur. Spinal Cord 50, 259–263 (2012). https://doi.org/10.1038/sc.2011.132
- Khaku AS, Tadi P. Cerebrovascular Disease. [Updated 2021 Aug 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK430927/
- Krishnamurthi RV, Feigin VL, Forouzanfar MH, et al. Global and regional burden of first-ever ischaemic and haemorrhagic stroke during 1990-2010: findings from the Global Burden of Disease Study 2010. Lancet Glob Health. 2013;1(5):e259-e281. doi:10.1016/S2214-109X(13)70089-5
- Coleman ER, Moudgal R, Lang K, et al. Early Rehabilitation After Stroke: a Narrative Review. Curr Atheroscler Rep. 2017;19(12):59. Published 2017 Nov 7. doi:10.1007/s11883-017-0686-6
- Puderbaugh M, Emmady PD. Neuroplasticity. In: StatPearls. Treasure Island (FL): StatPearls Publishing; July 22, 2021.
- Voss P, Thomas ME, Cisneros-Franco JM, de Villers-Sidani É. Dynamic brains and the changing rules OF NEUROPLASTICITY: Implications for learning and recovery. Frontiers in Psychology. 2017;8. doi:10.3389/fpsyg.2017.01657
- Sophie Su YR, Veeravagu A, Grant G. Neuroplasticity after Traumatic Brain Injury. In: Laskowitz D, Grant G, editors. Translational Research in Traumatic Brain Injury. Boca Raton (FL): CRC Press/Taylor and Francis Group; 2016. Chapter 8. Available from: https://www.ncbi.nlm.nih.gov/books/NBK326735/
- Group ATC. Efficacy and safety of very early mobilisation within 24 h of stroke onset (AVERT): a randomised controlled trial. 2015;386(9988):46–55. https://doi.org/10.1016/S0140-6736(15)60690-0.
- Bernhardt J, Churilov L, Ellery F, Collier J, Chamberlain J, Langhorne P, et al. Prespecified dose-response analysis for a very early rehabilitation trial (AVERT) 2016;86(23):2138–45. https://doi.org/10.1212/WNL.0000000000002459.
- Kwakkel G, Winters C, van Wegen EE, et al. Effects of Unilateral Upper Limb Training in Two Distinct Prognostic Groups Early After Stroke: The EXPLICIT-Stroke Randomized Clinical Trial. Neurorehabil Neural Repair. 2016;30(9):804-816. doi:10.1177/1545968315624784
- Nouwens F, de Lau LML, Visch-Brink EG, van de Sandt-Koenderman WME, Lingsma HF, Goosen S, et al. Efficacy of early cognitive-linguistic treatment for aphasia due to stroke: a randomised controlled trial (Rotterdam Aphasia Therapy Study-3) Eur Stroke J. 2017;2(2):126–36. https://doi.org/10.1177/2396987317698327.