Our brain is extraordinarily plastic. Not in the Tupperware and Barbie doll kind of way -- in the neuroscience field plasticity means the amazing ability of our brains to change and to adapt to pretty much everything that happens to us. There were times when scientists believed that once you’re out of the sweet childhood years your brain is like a dried clay pot, stuck in one form only. Yet tons of research has proved them wrong -- the brain turned out to be much more like play-doh. These changes can occur on very different scales: From a single neuron changing its connection to a whole cortical area shrinking or getting larger. There is plenty of factors altering the way your brain is wired including injury and stroke, as well as less tragic ones such as meditation, exercise or having piano lessons every day. As with everything in life, plasticity has two sides -- A side where your brain can reorganise itself during the after-stroke rehabilitation and the (dark) side where you are plagued by phantom pain after losing a limb. So let’s see how and what and why it all happens.
Let’s start with the small scale and talk about synaptic plasticity (for those who are not really certain on what exactly a synapse means: check out my Brain101). This type of plasticity, often referred to as long-term potentiation (LTP) and long-term depression (LTD) is central to our understanding of learning and memory. It -- very simplistically -- works like this: Connections between neurons get stronger or weaker (=potentiated or depressed) based on their activity. When neuron A repeatedly drives the activity of neuron B the connection between them grows stronger.
Naturally, this normally happens on more than one synapse -- whole new networks can arise if they were active in this precise constellation enough times (and this how we think memories are formed, by the way). So kiss your SO while listening to Lou Vega often enough and soon just hearing “Mambo number five” will put you in a romantic mood. Donald Hebb, Canadian neuropsychologist, coined the phrase “What fires together, wires together” to describe this process. At first, these connections are fragile, but if you activate them enough times, eventually they’ll become hard-wired (and just as inseparable as Britney and Justin in ‘99). The counterpart to it, LTD, is triggered by another pattern of stimulation and is thought to weaken the connections you don’t need -- forgetting your ex’s name or refining new dancing steps. Synaptic plasticity is the concept behind what the cognitive-behavioural therapists want their patients to do: To change the rigid thought patterns and, step by step, establish new pathways by practicing, practicing and practicing. These pathways progress from being country roads to fully developed highways (transporting healthy behaviour) while the dysfunctional circuits slowly fall into oblivion.
Plasticity on a bigger scale manifests itself in different ways. A growing body of research shows that the more you use a specific muscle the more territory the brain dedicates to it. For instance, there is a study showing that while our finger movement areas are generally of a relatively similar size it doesn’t necessarily need to stay this way. After five days of practicing a piano exercise certain substantial changes in the participants’ motor cortex were found. The motor areas responsible for the fingers have expanded and took over parts of the neighbouring areas just like weeds spreading over your garden. The researchers thought big and went one step further: They also showed that the mere act of thinking about practicing this exercise had a similar effect! Mental practice seems to be as efficient in reorganising the brain structure as the physical one. Another example (which neuroscience students have probably heard more often than the Bible Belt children heard about Jesus) is the London taxi drivers. Experienced cabbies who have to memorise the map of the capital including tens of thousands of streets and dozens of landmarks has been shown to have a bigger posterior hippocampus, the brain structure processing spatial memory and orientation. The control group, the bus drivers, whose routes are predetermined and well-established, on the other hand, were stuck with their original hippocampus size. To counter the inevitable comments regarding “correlation does not equal causation” (meaning what if bigger hippocampi and thus better navigation skills led the cabbies to choose this job?) the researchers showed that the volume increase of the posterior hippocampus was positively correlated with the time spent as a driver. The longer you drive the more you brain adapts to it.
Are you already convinced how damn plastic our brain is? Well, bear with me because there is more. If you’ve ever dismissed meditation as hippie nonsense consider this: Long-term meditational practice is actually associated with plenty beneficial changes to your brain. Just see it as training -- just like the piano lessons. Studies have shown that sitting still and being mindful will bring you increased cortical thickness (meaning more gray matter meaning more neurons dedicated to process stuff) in areas associated with attention, memory and emotional regulation. Moreover, meditation made amygdala, our center for fearful and aversive reactions, shrink in size and weakened its connections to the prefrontal cortex, the place where the higher executive functions sit. Basically it allows you to respond to stress more thoughtfully and suppress the primal emotions a bit (again: for more info on these structures check my Brain101). Last but not least, the default mode network, responsible for our sense of self and day-dreaming, was also rendered less active, allowing people to ruminate less (and prevent your thoughts from jumping from the yesterday’s party to the inevitability of death or something). And while I’m sneakily promoting healthy lifestyle here’s another thing changing your brain for the better: Exercise. Already as little as three hours of brisk walking a week leads to increased neurogenesis (=birth of new nerve cells) which, in turn, prevents age-related brain shrinkage. Studies have shown that especially frontal regions and hippocampus benefit from it -- meaning that their volume has increased after a prolonged exercise period. So memory and reasoning are back at it again, benefiting from healthy lifestyle choices.
Just as your spouse is supposed to be, your brain is with you in good times and in bad, in sickness and in health. So after you suffer a brain injury or a stroke, neuroplasticity is there for you. Rehabilitative training after a stroke or an injury has been repeatedly shown to reorganise the affected region. Say a stroke hits the area moving your left arm. Using a technique called constraint-induced moving therapy (where you are basically forced to use your “bad” arm while your “good” arm is being constrained) leads to an increase in the gray matter volume in the motor cortex, makes the regions adjacent to the affected one partially take over its functions and even make the contralateral hemisphere to participate in the recovery. Brain reorganises itself in order to adjust to the new circumstances and to make the best out of it. However, it is not always that nice. Sometimes the brain can be quite a bitch and cause you some trouble; I’m talking phantom limbs here. You have probably heard of people who still feel their amputated legs or arms. This too is done by our fidgety plastic brain, although it is still not 100% clear how exactly it happens. The most common theory is that the area of the somatosensory cortex neighbouring the one responsible for the missing limb seizes the opportunity and just takes over the vacant space. For instance, the face area is located right next to the arm area. So after the arm is no longer there this face area takes over its neighbour and double-perceives all the face sensations: both as coming from your cheek and from the non-existent thumb.
It becomes clear that we are not completely stuck with the cards the nature dealt us: It is still possible to update some of them (and this will not even be considered cheating). The brain reflects our environment, our decisions, emotions and life style and it is never too late to change it a bit, really.
Piano and plasticity 1, 2
Meditation and DMN
Meditation and amygdala
Meditation and increased cortical thickness
Brain and exercise 1, 2
Constraint-induced movement therapy
A great meditation resource suited for beginners which I'm using
Pictures by Toma