Tuesday, December 18, 2007

A Few Types of Learning

In reference to The Devil is in the Details:

Learning seems to be a recurring theme in this blog, so let's take it even further. Kandel says, "learning is in the synapses". How many kinds are there? Probably more than I have listed here, but this is a start:

1. Long Term Potentiation

Lately I've become caught up with Geörgy Buzsáki and his book Rhythms of the Brain. In chasing down things I've spotted in that book, namely the role of the hippocampus, the connection between theta rhythm and movement, orientation (space maps), memory and learning, it seems long term potentiation is A main if not THE main mechanism. "Learning" requires receptor breakdown and building, a process that is going on all the time anyway.. but when a signal comes in, repeatedly, the receptors will strengthen around the signal. (This is true for pain reduction, which is another sort of "learning", extinction learning, point 5.)

There is a very nice article from "Go Animal", a website linked in this blogpost by the same name. It's called "The Greatest Discovery You've Never Heard Of" by physical educator Frank Forencich.

Longterm potentiation (LTP) relates back to one of the other "tenets of neuroplasticity",
4. Initial changes are just temporary. While the brain can learn through impact (a powerful experience), usually it learns through lots of repetition.

In fact, we likely do NOT want to have to learn too many things through impact - such learning would tend to retain a heavy emotional overlay I should think, which could mess up integration, create large "hooks" for future learning of an inappropriate or counterproductive sort. Remember this other tenet:
5. Brain plasticity is a two-way street; it can change itself in positive or in negative directions. E.g., chronic pain, bad habits

... which leads us to another form of learning,

2. Sensitization

We know about this one from pain science, but its origins are with Kandel according to this Wiki page. This is described as short-term memory formation.

One of the most troubling (and confusing) aspects of pain states is mechanoreceptor sensitization, discussed in the Textbook of Pain, 5th ed.. This has led practitioners on merry goose chases after "the tissue at fault" (structure as opposed to function) for decades, centuries...

Sensitization can be "un"-learned, and quite rapidly, by something as easy as mirror therapy.

To overcome sensitization, and to utilize longterm potentiation, a "graded exposure" approach is usually recommended - this is a cognitive-behavioral approach which breaks down a learning or an un-learning movement objective into small, easily assimilative bits.

This ties in with

3. Habituation

This type of learning seems to be about just adapting to (learning to ignore) something in the environment or inside, consciously or unconsciously, be it initially positive or negative, although psychology definitions hold out for "decline in the response elicited by repeated stimulation, not due simply to adaption". My pick is "A decrease in the behavioural response to a repeated, benign stimulus." This would be best avoided in treatment of pain. I doubt we want our patients to "habituate" to either us OR our treatment. Which is why we should stay nimble and novel, in my opinion.

Habituation is classified as non-associative in psychology, which takes us to ..

4. Learning by Association, or Classical Conditioning

Here, the relationship between a stimulus and a response is strengthened, or (see above) "sensitized".

Here is one more:

5. Extinction Learning
We are now back with definitions that involve proteins at the neuron level of memory.

While this little list of definitions hops around among scholarly domains and perspectives, it is important to realize that, as per Kandel, nothing can happen with learning and memory regardless of domain, unless neurons and their receptors change. When dealing with patients whose overriding issue is persisting pain, the "locus of control" (another one of those catchy psych terms) must be with the patient at all times. They must be given ample opportunity to "learn" to downregulate their not-very-successful prior sensitization learning, given support, and sufficient time, especially if manual treatment (a form of exteroceptive neuromodulation) is involved.

Matthias, can you think of any other types of neural learning to add to the list?

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