We are currently taking a pitstop in our road trip across the discipline of neurobiology at the cabin of our eccentric yet indispensable friend, glutamate. If it were not for glutamate, studying for the SAT/ACT or even memorizing the lyrics of your favorite song would be an impossible task. Or perhaps you have a beef with glutamate when you’re trying to cram a semester’s worth of information into your brain during an all-nighter. Hopefully, by reading this article, you will gain an appreciation for the importance of glutamate and its nonlinear threshold in cerebral functioning. Glutamate is the neurochemical glue at the heart of learning.
As aforementioned in another article, glutamate is the primary excitatory neurotransmitter of the nervous system. An ample amount of this neurotransmitter can be found in the hippocampi, two brain structures of the limbic system that is instrumental to fact based memory, personal identity, and systems consolidation. It is implicated with learning and memory. Glutamate is so excitatory that it can actually excite cells to death, which is known as “excitotoxicity.” (1) In fact, when glutamate is released excessively, it can cause brain damage after a stroke. Because of this uber-toxicity, glutamate cannot penetrate the blood-brain barrier and can only be created from within the brain at certain glutamate generation sites. People who suffer from Huntington’s disease, a fatal neurodegenerative genetic disorder that causes the progressive breakdown of nerve cells in the brain, have nerve cells’ monster apoptosis precipitated by an overabundance of glutamate (2). Glutamate has also been associated with ALS, major depressive disorder, and multiple sclerosis. On the opposite end of the spectrum, low levels of glutamate have been associated with autism spectrum disorder in mice, and adults with major psychiatric disorders are believed to have lower levels of glutamate than “healthy” adults (3).
Imagine this: it’s October, mid-term season. Two roommates take the same course, Neuroscience 101. One roommate begins preparing for the exam way ahead of time, allocating two hours every night for three weeks to thoroughly study and comprehend the material. The other roommate, doped up on caffeine, decides that studying for 12 hours the night before the exam is the way to go. Sound familiar? Who will get the better grade? Obviously, the student who started studying earlier will get the better grade, but why? Three key players are instrumental in understanding why cramming for an exam is not beneficial: glutamate, long-term potentiation, and the nonlinear threshold.
Long-term potentiation (LTP) is the long-term strengthening of the synapse at the glutamate receptor sites usually in the hippocampi. When LTP occurs, an action potential is more likely to be generated. When the synapse finally reacts—the synapse has been potentiated— and learning takes place. The nonlinear threshold means that the neuron must reach a certain neurophysiological threshold before it can fire, which is why repetition breeds learning. By allowing for your brain to repeatedly see facts about the founding of America or the parts of the brain, your glutamate synapses are being strengthened, until after the nth time of reading the material, your brain can finally encode, store, and retrieve the information. So next time you’re studying for a major test, do yourself and your glutamate receptors a favor by studying in advance.
There is a major implication with tying glutamate to learning and intelligence. Would it be safe to say that those humans who naturally score high on intelligence tests, such as IQ, SAT, ACT, etc. have high levels of glutamate and great amounts of glutamate receptors? Would it be safe to say that those chronically underachieving students have low levels of glutamate? Could the synthesization and sale of glutamate for intelligence purposes be the next neurobiological controversy? Only time will tell.
In my next article, we will stop at a popular rest stop for high school and college students alike: the peripheral nervous system and its subdivision, the sympathetic nervous system, also known as the stress response.
References and Footnotes