The Science of Study
Medical students spend a lot of their time, if not the majority or entirety, studying. Attempting to learn all they can about every facet of the human body and the knowledge base that has been growing since the beginning of time… not an easy task to undertake. But what is not studied much is how we even retain all of this information. Little is known about the exact mechanisms and locations and processes used to gather, organize, and recall learned things, be it tasks, skills, facts, or experiences. What we do know is rather fascinating though, and quite apt to try and understand for the small subset of people who dedicate 5 years of their lives trying to retain and implement medical knowledge for the betterment of their fellow man.
What came first, the memory or the theory?
Let’s begin with how the theory of memory formation evolved. Aristotle gave the first hypothesis for memory, stating that there is a natural memory which is the memory that we use in everyday lives (remembering names, dates, places we’ve been, what we need to do) and an artificial memory that is utilised for learned processes and skills (when you learn to write, read, or speak). With this being the “accepted” form of memory in antiquated models, Aristotle said that humans were empty vessels, having no memories at birth and began to build from the day they are born inside this model of memories. As others began to propose models, it was suggested that neurons were responsible for the formation of memories as opposed to separate “memory aparati” in the brain. This then moved to the idea that some memories last longer, giving rise to our understanding of long-term and short-term memories. Next, a physical trace was proposed to be left on neurons, and this followed into further studies leading to the current understanding of long-term potentiation (LTP) and neural plasticity.
Still, this brief history leaves us with some outstanding questions. Where does memory localize in the brain? How do neurons actually store these memories? What biomechanical properties allow for these things to be stored? And most importantly, how do we recall these previous memories and rely on that knowledge to affect our decisions?
Location, location, location
With the increases to medical imaging over the years, studies from determined minds have led us to find areas of high activity with regards to memory. We have to be careful with our words here because we do only know where there is high activity. The area in question is the hippocampus, located underneath the cortex. The area is focused on long term memory as well as recall of locations and people. That being said, it’s been found in many tests performed on brain-damaged individuals that memories can still be formed, depending on type of memory. For instance, someone with damage to the front cortex can have difficulty learning new skills and retaining short-term memory, but has perfect recall of long term memories. This demonstrates that more than just the hippocampus is involved in learning. It is a highly complex process that calls more than just one area into the mix.
Pieces of the Memory Puzzle
Recently, more work has been done in involving how the neurons in the various parts of the brain retain these memories. Essentially this can be simplified to repeated exposure gives sensitization to the information at hand. This is why repetition is stressed heavily for learning new material! (link to repetition article) A cell is exposed to a stimulus which produces a current along the axon. When it arrives at the axon terminal, the current stimulates calcium to rush into the cell which triggers the release of vesicles releasing neurotransmitters to stimulate the motor neurons. With repeat exposure though, serotonin (5-HT) is released, beginning a cascade to the sensory neurons (5-HT > cAMP > PKA > CREB) and through phosphorylation, changes the genetic expression of the cell. Once these genetic expression take place, the ‘memory’ or ‘learning’ is sensitized for that cell and, in a very simplistic explanation, allows for recall of knowledge. That’s a lot to remember when you are a child and learn 2+2=4 for the first time!
While the jury is still out on the exact mechanisms and parts of the brain that allow this incredible and complex process to function, we do have a good understanding of learning. Now the key is repeating these steps over and over until you’ve sensitized your cells to retain how you learn… or click the links below to go over the mechanism in more detail.