BiologyNeuroscience

Remember that time?

Since everyone in Years 11 and above will be, or at least should be, studying for exams around this time of year, it might be fun to think about the actual process of learning/memory itself. Before we start though,  it’s worth mentioning that with a topic like this it is far too easy to start considering the implications of consciousness, mind vs. brain and then a downward (or upward?) spiral into impressive existentialist thoughts. For the sake of my simplicity I’d like to keep this post to a strictly structural discussion.

Communication

Before getting into how memory works, we just need to cover how the brain works… Herein lies the first issue, understanding of the brain and its operation is forever changing, occasionally even in the wrong direction but this is what makes the subject so attractive, it is literally a grey area. It follows that our understanding of how memory works is also constantly changing, their have been countless models presented over the decades, some disproved and some still stand.  To really get into any detail though we need to get a vague idea of how information is transferred through the nervous system – on a small scale at the very least.

1280px-Neuron.svg

Above, we have a nerve cell with inputs (dendrites), processes (cell body and long axon) and outputs (terminals) which are in contact with other inputs but NOT physically connected – these gaps are known as synapses. On our dendrites we have receptors and when these are stimulated, by a neurotransmitter for instance, a small number of ions are allowed into the cell. Now increase the input, more frequent stimulation, we get more and more ions entering the cell and when this process reaches a threshold value, a comparatively huge number of ions are allowed into the cell body, down the axon and to the terminal. At the terminal, the release of neurotransmitter is stimulated and the process starts over all within fractions of a second. Again, this is a simplified model, there are a number of intricacies and details missed but by and large, this is how information is transferred through the nervous system.

We’ve looked at how one neuron ‘talks’ to another but to put this into perspective, we have (roughly) 100 billion neurons each connected to 10,000 others which puts us up to a grand total of (very roughly) a quadrillion synapses. For further perspective that’s more than 3000 times the number of stars in the Milky Way and it is this very galaxy of interacting neurons that gives rise to intelligence, consciousness and memory too.

Changes

As you’ve been reading this post you may have picked up little bits of information and if asked too tomorrow, you might be able to recall a few facts you just read – so it has to be stored somewhere, right? It’s at this point that we need to move away from any tidy thoughts about Hard drives or RAM, whilst there are certain centres associated with memory (Hippocampus), there are a number of processes that run in parallel elsewhere. You can feel this at work when you associate a certain memory with a feeling for example, when I recall yesterday afternoon I ‘think’ the smell of tea, the warmth of the sun and maybe even hear a lawnmower. Again, the processes here are numerous and complex but we can apply them on the smallest scale to our model of neuron communication.

When something is learnt, there has to be a change in the brain. Let’s use the example of juggling, initially as I fumble around, the motion is unnatural but a few days and hours of practice later and it’s increasingly easy to keep the motion going. Essentially, repetition drives memory, we know this from experience. If we combine this with the fact that information travels through the nervous system by activation, it leads to the explanation that repetition makes it easier to activate the neurons in a pathway. Again, back to our model, this means that the threshold of ions is reached more easily. This isn’t done by a change in the neuron itself, the careful chemical equilibria present makes that unfeasible. Instead, the change occurs in the gaps we mentioned – synapses. We want, for the same unit quanta of neurotransmitter, a heightened response in the neuron. This is done by ‘up-regulation’ of the receptors, which just means we get more of them. So, as I learn to juggle, the synapses in the pathway(s) involved are up-regulated making the pathway more easily excitable and the motion easier.

By Giri Nandakumar

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