Differences in the Size and Activity levels of Brain Parts: Long-Term Potentiation

One of the ongoing themes of this blog is the nonsensical practice of some researchers in psychiatry of routinely labeling differences in size and activity levels of parts of the brain, as seen on brain scans such as fMRI scans, between various diagnostic groups and control subjects as abnormalities (See the posts http://davidmallenmd.blogspot.com/2010/03/neural-plasticity.html and http://davidmallenmd.blogspot.com/2013/02/neural-plasticity-and-error-management.html).

These researchers seem oblivious to a now well-established process within neurons called long term potentiation (LTP). Briefly, if a synapse – the point between two nerve cells at which a nervous electrical impulse passes from one neuron to the other – is stimulated by individuals’ interactions with the environment that leads to learning, this produces a long-lasting increase in signal transmission between the synapses of those two cells. In other words, the power of the connection starts to increase. Conversely, if such a connection is hardly ever stimulated, its power decreases. This is probably the way memory works. Hearing a fact once in a lecture may not lead to its being remembered for long, whereas if someone keeps studying the fact, the memory of it becomes stronger.

It is important to mention that structural changes in the size and shape of the pre- and post-synapse parts of neurons may mediate permanent or near-permanent changes in synaptic efficacy. Growth may allow for an increase in the size or number of active zones on both sides of the synapse. The “spines” of the cell can increase in volume after LTP induction. While the degree to which structural re-organization of synapses occurs in adult animals is not yet clear, the process seems to involve a neurotransmitter (a chemical substance that is released at the end of a neuron cell by the arrival of a nerve impulse and, by diffusing across the junction, causes the transfer of the impulse to another neuron) called brain-derived neurotrophic factor (BDNF).

If a particular synapse is almost never stimulated, it can disappear altogether. Conversely, LTP is associated with an enhanced recycling of a part of the structure of the synapse, and this process could eventually result in the formation of a new, immature spine.

In other words, the more a part of the brain used for a particular purpose is used, the more likely it is to increase in size due to this process. When many synapses are involved in an individual's interactions with the environment, size differences in those parts of the brain can therefore easily be conditioned responses rather than abnormalities.