The brain’s capacity to learn

Learning a new skill - in my case, Javascript and web development - can be full of exciting moments of understanding but also of challenges and self-doubt. During the latter, sometimes I just need a refreshing perspective in order to return to a positive and productive mentality.

I like to get this fresh perspective by looking at the natural world. Specifically, this time I turned my curiosity to the brain and neurobiology.

I know a simple thing like listening to music can have powerful effects on my mood and motivation, which made me think about the short-term changes that must be occuring in my brain in response to the sounds I’m hearing. My brain is firing, that’s a good start. So, what about long term changes in the brain? What is the process of learning at the molecular level?

There is a term to describe the ability of our nervous system, which includes our brain, to change in response to stimuli - plasticity. In response to extrinsic or intrinsic stimuli the brain is capable of reorganising its structures, functions and connections.¹

These changes can take effect across different space scales and time scales. For example, plasticity can be observed at different regions of individual neurons or whole regions of brain when compensating for brain damage.^{1, 2, 3} Plasticity can also be observed quickly over seconds to minutes like in the case of changes in postsynaptic potentials that either enhance or depress the chances of an action potential firing (the release of dopamine while listening to music can act as a neuromodulator and affect these potentials^{4, 5, 6}). Or the brain can change in response to stimuli over minutes and hours by ways such as Long Term Potentiation (LTP) and Long Term Depression (LTD)^2,7 or even over longer time periods such as with homeostatic plasticity.⁸

Changes that strengthen or weaken transmission at the synapse between individual neurons, either over shorter or longer time scales, are known as synaptic plasticity. Synaptic plasticity is said to be the underlying cellular mechanism for learning and memory.⁹ However, due to the difficulties of looking inside the human brain while keeping it in full working condition(!), the total extent to which this applies to the human brain is not yet known.⁹

To learn something that might potentially last a life time, the brain has to be able to maintain its new functional and structural changes. This is a reason why LTP and LTD, forms of synaptic plasticity, are important. People often say “practice makes perfect”. Well, by repeating something over and over an activity-dependent plasticity can be observed (as opposed to reactive plasticity, like when the brain needs to reorganise due to injury). Strengthening and weakening of neuron connections (both are thought to be necessary for learning and for neuron signalling to change dynamically) can happen in a “Hebbian” style or ”non-Hebbian” style.¹⁰ Hebbian forms of LTP and LTD follow Hebb’s postulate, which can be simplified to: neurons that fire together, wire together, while neurons that fire out of sync, lose their link.¹¹ That is, after repeated stimulation or lack of stimulation the synapse strengthens or weakens, respectively. Non-Hebbian synaptic strengthening and weakening is basically the opposite - when the presynaptic neuron and the postsynaptic neuron fire together the synaptic transmission tends to weaken.

Figure 1. NMDA-receptor-dependent LTP is a type of Hebbian synaptic plasticity. NMDA receptor in green. LTP is the strengthening of the synapse (LTD is the weakening of the synapse). This strengthening can occur by an increase of neurotransmitters released into the synapse, an increase in number of receptors on the post-synaptic neuron and an increase in receptors’ downstream effects.

It has been hard to make causal links between specific changes in the brain and the resulting learnt abilities, but using monkey brain-computer interfaces, researchers demonstrated that new neural patterns did correlate with new behaviours in the animals.¹²

Synaptic plasticity may be one of the most well studied mechanisms of learning and memory, but it certainly isn’t the only one. Whereas functional plasticity (like LTP and LTD synaptic plasticity) is thought to be able to occur quickly, structural reorganisation and formation of new cellular components is thought to occur over longer timescales.¹³ There used to be limited evidence showing structural changes occuring in response to learning in human brains following functional change.¹⁴ It had been previously thought that the brain is most “plastic” during development and that no new neurons are created during adulthood. While the juvenile brain does indeed experience more cell growth and can more easily undergo neuroplastic change, the adult brain exhibits both too. Research suggests that learning in adults is associated with structural change that goes beyond synaptic plasticity,^{15,16, 17} even in a short period of time¹³ (adult brains might just need a little more effort and focus¹⁵). There are associations between learning and changes in brain function and structure at every level, but researchers have yet to bridge the gap between a lot of in vivo and in vitro experiments that study the exact effect that plasticity has on learning and memory. As with most areas of science, we really have just scraped the top of what there is to uncover (which, to me, is really exciting).

Ok, so neuroplasticy is a characteristic of our brains. Can we improve it though? There are some things we obviously can’t do anything about (yet!), like our age and genetics.^{18, 19} There is still a lot we can do to help,^{20, 21, 22} like looking after ourselves the good ol’ fashioned way - eating a healthy and balanced diet,^{23, 24, 25} sleeping well,^26,27 exercising²⁸ and practising meditation.^{20, 29} These activities can also help our overall health and brain chemistry in other ways, like fighting depression, which might also make it easier to take the first step to learning something new.

So, after all that, I’m feeling pretty positive about tackling a new skill and being able to learn Javascript and web development (I’ve at least been able to deploy a blog 🙃). Aside from the good that trying to learn something new can do for the brain and health, there are most likely other personal reasons for taking up a new skill, like if it’s something you’ve always wanted to do, or if it will help steer you in the direction of your passions. Just give it a go!

So, of course there will be times when we struggle while learning something new. At those times, however, I like to imagine I’m struggling because my brain is actively making new neural connections.

References