Neuroplasticity: Changing the Brain at Any Age
I have a friend who works in humanitarian aid and has raised her daughter in multiple countries. By the age of seven, her daughter was fluent in English, Spanish, Bosnian, Serbian, Albanian, and Tagalog. Why is it that kids "are like sponges" and seem to pick up foreign languages just by being exposed to them? The answer lies in neuroplasticity. Neuroplasticity is our brain's ability to develop new neuronal pathways and networks based on the input we provide it, that is to say, the experiences to which we expose ourselves.
We have known children to have this capability, especially within the first 7 years of their lives known as the "critical period". But what about adults? And older adults for that matter? It wasn't until relatively recently that we discovered the adult, and yes the older adult, brain has the capacity to change its neuronal structure (new neurons) and function (how they operate).
The Homunculus (now 3 times really fast)
Through the experimental graces of rats, monkeys, and even owls and raccoons, almost a decade of neuroscience research has taught us that specific brain regions are responsible for specific sensory processing (feeling) and motor responses (doing). For example, when you dip your toe into the cold ocean, the temperature receptors on the skin of your toe send signals up a neuronal highway to the very specific region in the brain responsible for sensations of that particular toe. Other nearby regions in the brain receive sensory information from other toes, or from the bottom of your foot, or your ankle, all the way up to the tippy top of your head. Likewise, if you wiggle that toe in the cold water (cause you LOVE cold water dipping like me!), there is a very specific part of your brain allocated to the movement of that toe that sends signals down a neuronal highway to wiggle that toe, or wiggle the other toes, or the foot, the ankle, or your entire body. Scientists discovered this over years of "mapping the brain". Stimulating one part of the brain, and noting which body part moved, which muscle contracted, allowed them to map the motor cortex. Or stimulating a part of the body, and noting which part of the brain activated, allowed them to map the somatosensory cortex. A pictorial summary of these maps, known as a homunculus, are below.
Neuroscientists Michael Merzenich, Jon Kaas, and Karl Lashley took this knowledge a step further and discovered that these maps are not set in stone or written in ink, but rather drawn in say...chalk. Meaning, that these maps can change! Lashley, while mapping the motor cortex of one particular monkey (let's call him Yek), discovered that Yek's sister, Nom, had a different motor map. When he compared Yek and Nom's motor maps to other monkeys of the same species, he found that all of their motor maps had significant variations. He also found that if he re-mapped Yek's motor cortex and compared that to a previous map of Yek's motor cortex, they were different! He concluded that these motor maps are adaptable and depend on how much a particular movement is performed. For example in humans, the motor map of the shoulder (located near the top of that homunculus) of a regular swimmer will be physically larger than that of someone who doesn't use their shoulder muscles as much, or will even be different in that same swimmer if they stop swimming. Can you imagine the size of Katie Ladecky's shoulder motor map???
Likewise, Merzenich and Kaas, while mapping the somatosensory cortex in monkeys noted that if you amputate one of the monkey's fingers, the somatosensory map of that finger will be taken over by the somatosensory maps of the remaining fingers. They also discovered that if you re-attached that finger, and encourage the monkey to use that finger in various activities, over time it will reclaim it's brain territory and establish it's somatosensory map once again! Tell me this isn't blowing your mind? Honestly, even as old news to a neuro-geek like myself, my mind continues to be re-blown as I write this.
Anyway...why am I, a physical therapist, concerned with all of this? Well, as a neurological physical therapist, this is the basis for helping people recover movement function after a brain injury, stroke, or vestibular condition. So, how do we do that?
How can I change my brain? Principles of neuroplasticity
Leveraging the findings of multiple studies in neuroplasticity, Kleim and Jones outlined ten principles of neuroplasticity that we, as physical therapists, use to help people rebuild their brain after injury. Click the arrows to learn more about each principle.
Use It or Lose It
Remember those monkey's that had one of their digits amputated? Unable to use that digit, the part of the brain responsible for the feeling and movement of that digit was lost and taken over by the other digits that were being used regularly. If you don't use a particular movement pattern or stop doing it you will lose it. So first thing in therapy, is simply to start doing the thing you want your body to do and to keep doing it.
Use It and Improve It
Doing the activity does not only maintain your ability to do it, but can also improve that ability. We see this in cases of people after they've had a stroke. Oftentimes, the affected side of their body may be weaker, less coordinated, or difficult to use to perform daily tasks, so they rely on their unaffected, or stronger side. This will only improve the stronger side. A physical therapist may introduce constraint-induced movement therapy (CIMT) to restrain the arm on the non-affected side so that the patient is compelled to use their affected limb as much as possible and improve its function.
Specificity
I once had a swim coach who said "if you want to swim faster, you need to swim faster". Uh, thanks coach? It is important to provide patients with exercises specific to the activity or movement pattern they want to improve. For example, if you want to improve your ability to go up/down stairs, you need an exercise like stepping up/down on a single step. Likewise, if I have a patient who gets dizzy bending over while gardening, then I will give them an exercise that encourages this specific movement.
Repetition Matters
How many reps do I need to do in order to see change? While we don't have specific numbers on how many repetitions are required to induce neuroplastic change, we do know it's A LOT...like thousands and tens of thousands a lot. When inducing neuroplastic changes, your exercise program will not be to do 10 reps of an exercise. It may be to do 30 reps of an exercise, throughout your day, or starting a regular walking program in order to get thousands of steps in each day. This is why your HOME PROGRAM IS CRITICAL. You will not see change in how your body moves, or reduction in your dizziness symptoms, or improvement in your balance by going to physical therapy 1-2 times per week. You need to be doing these exercises EVERY DAY. Sorry for the all caps...it's the only way I know how to express the importance of this in writing.
Intensity Matters
This is a hot topic in neuro-rehabilitation and specifically in learning how to walk after a neurological insult. We now know that therapy needs to be intense, meaning working your heart rate into 70-80% of your max heart rate. This increases blood flow to the brain bringing necessary oxygen and nutrients, and increases the production of Brain Derived Neurotropic Factor (BDNF), the molecule responsible for neuroplasticity. However, intensity should be prescribed and monitored by a qualified healthcare professional who is taking into consideration any cardiovascular, pulmonary, or musculoskeletal co-morbidities and ensuring the activity is safe.
Time Matters
Neuroplasticity is more likely to occur sooner than later after the neurological event. The sooner you can start rehabilitation, the better. This is the time that your brain is trying to heal itself, so therapy can leverage that and encourage it to heal properly and avoid adopting maladaptive or compensatory movement patterns (see the principle of interference).
Salience Matters
As a former adult educator, this principle makes so much sense to me. The activity you are trying to improve or rehabilitate, needs to be important to the person or patient. Duh! If we are working on balance, I want to know what specific activities you do and enjoy that require balance. I recently worked with a woman who was a black belt in martial arts and wanted to get back to doing specific movement combinations requiring lunging and turning and bending over. Rather than giving her an exercises where she is walking and turning, we created an entire program based on the specific combos she uses in her martial arts. It was really motivating and fun (for her and for me!).
Age Matters
While younger brains may be more adaptable to training than older brains, there is evidence to support neuroplastic changes in the latter. One obvious example, is older adults' recovery from stroke. After damaging the brain due to an arterial blockage (ischemic stroke) or an arterial bleed (hemorrhagic stroke), we see people make significant functional recovery in the areas of mobility, speech, and cognition.
Transference or Generalization
Neuroplastic changes, and therefore acquisition of a specific skill, in response to a specific training stimuli in the clinic can transfer to a related skill outside of the clinic. For example, many of my patients with concussion and other vestibular diagnoses report visually induced dizziness, or dizziness in visually stimulating environments, such as a grocery store, watching movies on a big screen, or being on a zoom call. While I don't make them do these things in clinic, I do simulate these environments through the use of complex backgrounds, YouTube videos, or virtual reality. Practicing this in a controlled environment with minimal to no dizziness, allows them to tolerate more real life activities like grocery shopping, moving going, and that dreaded Zoom call.
Interference
I like to call this principle, negative or maladaptive neuroplasticity. Just as we can retrain our brain to perform useful tasks and reduce symptoms of dizziness and imbalance, we can also train our brain to perform compensatory movements or actually induce symptoms of dizziness and imbalance. I see this often with people who are delayed in getting rehabilitation and have trained their brain to move their body in a way might have served them in the short term, but can possibly be harmful to them in the long term. I also see this with patients who are dizzy and imbalanced due Persistent Postural Perceptual Dizziness (3PD) or Persisting Post-Concussive Symptoms (PPCS). While it's possible to change the brain again and train out those maladaptive processes, it can take a longer time than for someone who seeks rehab early on.
“Nothing inspires more reverence and awe in me than an old man who knows how to change his mind.”
― Santiago Ramón Y Cajal ("Father of Neuroscience")
References
Kleim JA, Jones TA. Principles of experience-dependent neural plasticity: implications for rehabilitation after brain damage. J Speech Lang Hear Res. 2008 Feb;51(1):S225-39.