Can the brain heal itself after a stroke?

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📓 The short answer

After a stroke, the brain can reorganize its neural pathways to recover lost functions through neuroplasticity. The best way to promote healing is consistent practice of the affected functions, like deliberately using the weaker side of the body for everyday tasks.

📚 The long answer

When someone has a stroke, an artery in the brain clogs or bursts. Blood flow stops. And for every minute a stroke goes untreated, 1.9 million neurons die.

This can strip away someone's ability to move, speak, remember — sometimes all three. But when the damage is done, can the brain heal itself after a stroke?

Yes, the brain has an extraordinary ability to heal itself after a stroke. But unlike healing a broken bone by rebuilding bone tissue, the brain is not simply creating new neurons (although this happens to some extent). The primary way a brain heals itself is through neuroplasticity.

What is neuroplasticity?

The brain contains billions of neurons, each of which can connect to up to 10,000 other neurons, forming a network of trillions of neural connections. These connections link specialized areas of the brain, enabling perception, movement, and memory.

Neuroplasticity is the brain's ability to reorganize these neural pathways based on what we learn and experience. While neuroplasticity is always happening, it kicks into a higher gear at certain moments in our lives, like when we're infants and toddlers or after a brain injury.

During the first weeks and months after a stroke, enhanced neuroplasticity allows the brain to form new neural pathways and even transfer functions from damaged sections to healthy areas.

Thanks to neuroplasticity, stroke damage doesn't always result in permanent loss of function. But how exactly does it work?

How does neuroplasticity heal the brain after a stroke?

Neuroplasticity works at two scales: at the level of individual neurons, and at the level of entire brain regions. Here's how both play out.

Mechanism #1: Axonal sprouting and dendritic branching

Each neuron has dendrites (which receive messages from other neurons) and an axon (which sends them). During neuroplasticity, these parts experience structural changes to rewire the brain.

With axonal sprouting, the neurons close to damaged areas extend their axons or sprout new axons to try to take over the functions of the damaged neurons.

Similarly, dendritic branching allows dendrites to grow new branches to form replacement connections. The brain isn't simply creating new neurons from scratch; it's calling on existing neurons to adapt.

Mechanism #2: Cortical reorganization

At a larger scale, the brain can reassign unaffected areas to take over the functions of damaged areas. Neighboring areas of the brain — or even the opposite hemisphere — may take over the jobs of damaged areas.

This happens in non-stroke patients too, like when someone loses a sense. For more on this topic, I recommend reading Livewired: The Inside Story of the Ever-Changing Brain by David Eagleman, which friend of the newsletter Rodrigo tipped me off to last year.

Mechanism #3: Synaptic plasticity

Neuroplasticity also involves strengthening or weakening the connections between neurons based on how often they're used. Put simply, the more we do something, the easier your brain makes it feel.

The clearest example comes from learning: The first time you try playing guitar, it'll feel awkward and difficult. But by the hundredth time you play, it feels natural.

What can a patient do to recover from a stroke?

The best evidence we have to treat post-stroke patients is to actively encourage the brain to rewire itself. The caveat here is that we need to compel the brain to rewire itself positively rather than negatively.

• Positive neuroplasticity happens when a patient consistently repeats challenging tasks to build new neural pathways.
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• Maladaptive neuroplasticity is when the brain rewires itself in an unhelpful way, reinforcing bad habits or compensatory movements that make recovery harder in the long run. In other words, the brain prunes away pathways it sees as unimportant if we're not doing them.

Here are some common post-stroke rehabilitation strategies that encourage positive neuroplasticity.

Constraint-induced movement therapy

This technique forces the patient to use the affected limb by restricting the movement of the unaffected limb. The patient will engage motor cortex areas that were affected by the stroke and encourage cortical reorganization.

Constraint-induced movement therapy (CIMT) can significantly improve the motor function of post-stroke patients, even months after the stroke. In a 2006 study, patients who did a two-week CIMT program improved their arm function +34% more than the control group.

Task-oriented training

This rehabilitation involves intentional, repetitive practice of real-world tasks to encourage positive neuroplasticity. For example, if a stroke resulted in limited movement on the right side of the body, a patient should intentionally practice doing things with their right side, like brushing their teeth or picking up a cup. Over time, this will lead to regaining function on the right side.

Speech therapy

A stroke can affect the muscles we use to speak, as well as the cognitive functions behind finding words and understanding language.

Speech therapy involves targeted exercises to regain motor function, like tongue movements, and language processing practices, like word games. A 2016 study found that stroke patients who received high-intensity speech therapy showed around 70% better language recovery than those who didn't.

Non-invasive brain stimulation

Beyond targeted practice, non-invasive brain stimulation is a promising technique that's been shown to improve outcomes for stroke patients.

Transcranial magnetic stimulation (TMS) and transcranial direct-current stimulation (tDCS) are outpatient procedures primarily being used to treat major depressive disorder and obsessive-compulsive disorder, but they are also showing promise in stroke patient rehabilitation.

These techniques involve using magnetic fields to stimulate neurons (TMS) or low electrical currents to increase or decrease the neural excitability (tDCS). They've been shown to facilitate neuroplasticity by triggering neurons to fire more in affected motor cortex areas or decreasing activity in the unaffected areas, which can interfere with recovery.

While it's not as widely used as other post-stroke therapies, these non-invasive brain stimulation techniques are increasingly being incorporated into rehabilitation programs. One 2012 study found that patients who received TMS had about a 65% chance of better motor recovery than control patients.

--- Thanks for reading this week's newsletter! If you have any thoughts, questions, or favorite GIFs, my inbox is always open. Just hit reply to send me a note! :) ​ All my best, Caitlin ​Click here to read five facts about Caitlin​

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​Sources for this week's newsletter​

🌐 Wikipedia article of the week

​Tiffany Problem​

"The Tiffany Problem, or Tiffany Effect, refers to the issue where a historical or realistic fact seems anachronistic or unrealistic to modern audiences of historical fiction, despite being accurate. This often occurs with names, terms, or practices that, although historically accurate, feel out of place because of modern associations....
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The name Tiffany derives from Theophania, a name for girls in medieval England and France. The old French form c. 1200 was Tifinie, and the spelling Tiffany first appears in English c. 1600. However, if a historical fiction writer were to name an English character Tiffany in an Early Modern European setting as early as 1600, the audience would likely perceive it as inaccurate, associating the name with contemporary times or the 1980s in particular when the name reached peak popularity."

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👀 Catch up on other curious questions

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