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Obsession with Chemical Mechanisms of Neurotransmission Led to an Inability to Learn about Short Term LearningThe neuroscience community was once divided between those who hypothesized that electricity flowed between neurons and researchers who believed that the synapses communicated principally by means of neurotransmitter chemicals. The biochemists won handily and the many discoveries about chemical communication between neurons have obsessed neuroscientists for the last four decades. Now it may be time for a revenge of the electrical engineers. This has already begun with the discovery of "electrical transduction between synapses" according to Ann Graybiel. (in conversation after her presentation to the MIT Hippocratic Society's 2003 Conference on Neuroscience). Based on a hunch developed after reading the K-line Theory of Memory (from Minsky's collection of ingenious essays, Society of Mind), I began to ponder how the connection strengths and hence the memories themselves were established. After writing the hypothesis up in a term paper, I borrowed The Neuron, a then recent (circa 1997) textbook. It said that signal is transmitted electrically within the neuron and conductance increases with diameter of the axons and dendrites. This was followed by a non sequitur. I searched the entire textbook and found no further elaboration or speculation that intra-neuron electrical conductivity could be fundamental to our understanding of how connection strength is modified, of how memory and skills are established. Biochemists developed proof of the major roles that changes in the number of neurotransmitter sites play in modifying the connection weights at the synapses. The success of the biochemical studies apparently caused other any electrical models to become unfashionable areas for research. It is generally believed that science and engineering tend to progress by picking up and then exhausting various themes (c.f. Gerald Holton). Towards the end, researchers carry on doing, and grantmakers continue funding, what they know. (It is the same herd mentality, or overshoot, that causes market bubbles.) But that's not the only reason that the electrical model became unpopular circa 1960. Imaging of in-vivo neural circuits was not then possible. The neurons of our mind may move a bit like wet sand. They must not be squeezed tight for long because this prevent their axons and dendrites from moving and realization from occurring. Thus relaxation is essential to learning and failure to relax leads to mania: poor memory, performance and stress. Too little love causes this and early death. IMHO, manic depression should be reclassified as a sleep disorder. There must be a Nobel for the first to definitively show how Ohm's Law links to taking care of yourself. Related References
Some (very cheeky) Details (for kids)I do not have access to my original term paper but wrote the following with middle school students in mind. The lightly colored text is for the the kids. Anybody can demonstrate by squeezing sand hard that certain kinds of materials will lock-up under pressure into a particular physical configuration. Is the brain made of stuff like that? Well, maybe. Neurons are, in a sense, like little animals living their own specialized ecosystem or community of cells. The brain has three types of cells. The two types neuroscientists talk about most are the neurons and their surrounding glial cells. But there is a third kind. I've asked neuroscientists to name them and they do not remember. What are they? Endothelial cells!!! Yes, boys and girls, these are the cells that make up the lining of the blood vessels. They are sooooo cooool! Why? Because they allow the pipes that carry our blood to expand and contract. Now, have you ever seen the water pipes in your house? Do they expand or contract??? No waaaaaaaaaaaaaaaY! (Are you asking me if I am a horse? Nay, I say. Now be quiet and pray while we proceed to flay the all the old docs with blood vessels and neurons like dry clay............. HEY. Hey, hey...) Did I hear someone also say glial cells? What do they do? Well, these are cells that protect the teeny tiny hungry little critters called neurons. You know, that society of cells which make up the nervous network, our brain and mind (but not our soul). As I was saying, the glial cells wrap around the neurons and protect them. Glial cells are very special because their cytoplasm (that is the liquid stuff inside cells) can flow to neighboring glial cells. They can deform and make space for their neighbors. If they are wrapped around neurons that suddenly need a lot of blood to feed their frenzied activity, glial cells can get really skinny. That is great because their thinness brings close the oxygen and sugars needed to power the active neurons. It also relieves the pressure from the blood vessels that would otherwise squeeze the neurons, make them smaller, less conductive and less able to fire. FIRE? Is there something burning in my brain? No wayyyy! But neurons work by firing electrically and the faster they fire, the more active the thought that they help to form. Glial cells might be like the referee at boxing match which let the contestants compete but not too much. Who is the prize fighter? The blood supply because it uses endothelial cells that get pushy very quickly when then are told to expand. The space they occupy is limited so glial cell walls must retreat when endothelial cell walls advance. When they fight too much, the blood supply gets blocked and we get headaches. These can usually be arrested quite easily and I'll tell and show you how if you ask. It is a lot quicker as safer than anything you can put in your body. But you will have to ask me. Otherwise, you will not believe it because it is so simple. Wise people know that chronic stress manifests as elevated blood pressure and heart rate and is marked by learning disability. These pressured periods coincide with taking action; that's when we show and do what we know. We learn much better when we are not stressed. If you are stressing on a problem, you are most likely to solve it when you relax. Is the corresponding drop in blood pressure simply a coincidence? Sleep causes blood pressure to drop. Could it be that that increases the motility of the neurons and plasticity of thought? Have you never had the "aha" phenomenon when, upon waking, the solution to a problem that was intractable problem the night before comes clearly and easily into mind? Learning occurs as a result of neurons changing their connection weights. If these are largely influenced by their shapes and corresponding internal electrical properties, then the contraction/expansion cycles of the local blood vessels will have a important effect on learning. Up/down patterns in activity, expression and stress occur on many timescales. There is a short cycle, such as the one that occurs when tutored students alternate between receptive listening and the more pressured state of expressing when writing and talking. There are longer stress periods during the day caused by activities like eating and exercise. Sleep is the main de-stress mechanism and, of course, we have the Sabbath day and vacations. All of the de-stressing periods are marked by a lowering of heart rate and blood pressure and are associated with increased receptiveness. Why is that? Occam's Razor suggests that one the main mechanisms involved in learning and forgetting is the heart/brain interaction. Could it be that a neuron is like like a grain of sand that becomes immobile under pressure that, when relieved, allows the motility required to make new connections or, by simple virtue of increasing the cross-sections of its axons and dendrites also increases their conductance and thus the role of that neuron? In-vivo imaging research will soon get to the point where the see-sawing movements of the blood vessels and functionally identifiable neurons can be shown and linked to learning. Use of vaso-effectors like alcohol (a dilator that causes learning impairment), or nicotine and nor-adrenalin (both vaso-constrictors associated with memory enhancement; the latter most probably responsible for the flash memorization effect caused by fright) are implicated in the neuro-transmitter systems as well so the classic demonstration will have to be rigorously designed. OOPS: (Here's a simple way to show yourself how important blood pressure regulation is to learning. First of all, do you know how to flatten your tummy, stand straight and tall? To do this, you need to stand and tighten your "six-pack" stomach muscles so that your pelvis tilts forward. (Don't do this rhythmically around other people unless you want them to get ideas.) If you can't see your six-pack, you might not have very strong stomach muscles so you might need to do 100 slow sit-ups a day for about four months. Or you might have a six-pack muscles but can't see them because you have tummy fat like most girls. In any case, the main thing is that you need strong muscles to stand straight and flatten your tummy. Once you can do that, go stand next to a couple of people who are taking about something you find difficult to understand. Keep your stomach as flat as possible for a few minutes and see how well you can remember what they are saying. Then relax your tummy muscles completely and see if this helps you to follow their conversation. Of course, this might have something to do with the fact that you are not breathing!. In this model, a crucial effect of sleep is the becoming sluggish and lowering the core temperature so that the blood vessels contract and especially the cerebral cortex which is the seat of imagination and consciousness. Some connections must get broken as the brain cools and contracts. Perhaps this occurs as the events of the previous day are explored in dreams associated with rapid eye movements known as REM sleep. It is essential to free up short term memory in order to be able to function well. Otherwise, depression results from being awoken by the alarm for a dumb job, or mania due to premature waking and acting on fear.
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