Neural Mechanisms underlying Motor Learning

Abstract

Learning new things is pleasant. Moreover, learning is crucial for our survival. In contrast to trees and plants, members of the animal kingdom, including us humans, can move freely in a constantly changing world. Therefore, all forms of animal life need the capacity to change their behavior in accordance with new environments. For instance, worms do remember the environment that predicts good food (Wen et al., 1997), and we humans easily remember where to find the best coffee machine at our work. The acquisition of this new behavior or knowledge is what we might call learning; the storage and retrieval of this behavior or knowledge is called memory. Our daily life experience is that our memory consists of an enormous heterogeneous collection. For instance, I know that Oliver Twist was written by Charles Dickens, that most readers of this dissertation will stop within a few sentences from here, that F.C. Ajax has beaten F.C. Barcelona with 2-0 in the 2013/2014 Champignons League group stage, etc. Each of these phrases beginning with “I know that…” can be classified as explicit memory. Explicit memory (also called declarative memory) includes memory for facts and events, which can be recalled consciously. In contrast, implicit memory (or non-declarative memory) covers all those cases in which a person or animal ‘knows how…’ to do something. I know how to swim, how to iceskate, but I do not have the capacity to fully explain it. The only way one can learn iceskating, is by simply doing it, by practicing it. Of course this subdivision in explicit and implicit memory is arbitrary and many, if not all, tasks involve both types of memory. For instance, when I learned ice-skating someone instructed me to bend a little more forward for keeping good balance - which was quite difficult w ith t hree pairs of socks in my mother’s white oversized ice skates. By applying this instruction in my actual skating, implicit and explicit knowledge are combined. But once more experienced, you just bend forward without even knowing that you do so. In general, explicit memory is easily acquired but also extinguishes very fast. How many history facts do we still know from the classes during high-school? In contrast, implicit memory is acquired slower and requires a lot of training and repetition. But, once learned, the memory is pretty solid compared to explicit memory. It always surprises me how easily you still can skate, even after years not doing it. One might therefore wonder if the two forms of memory are stored (i.e. ‘learned’) differently in the brain. Or, in other words, if the neuronal mechanisms underlying their formation and retrieval are different. This question of memory formation is not a new question. In Plato’s dialogue Theaetetus, which examines the question ‘What is knowledge?’, one of the characters argues that minds made out of soft wax are good at learning, but apt to forget, whereas those employing the hard wax are the reverse. Apart from the question whether we should interpret this statement literally or more poetically, we might call it one of the first neuroscientific learning theories. Explicitly, it tries to explain what happens in our brain when we are learning new things; it attempts to describe the neuronal mechanisms underlying memory formation. But, as philosophers do, it was all left it by pure speculation.