It all makes sense now, right?
When you stimulate different pathways surrounding the same memory—through repetition, studying, storytelling, association with other memories, or learning something through multiple sensory pathways (say, visually and aurally, like during a PowerPoint presentation)—you are actually constructing a cellular pathway. Each long-term memory physically changes your brain.
Deep inside your hippocampus, each of these activities is stimulating an electronic pathway using simple chemical reactions—firing the neurons—that repeatedly engage the same synapses, or groups of synapses. This strengthens the connection, and keeps it open for indefinite retrieval.
For example, let’s say you learn something in a class. Your professor explains photosynthesis, and draws a diagram on the chalkboard. This sends two different surges of electricity through the same group of synapses, opening and strengthening them. This probably isn’t the first time you’ve heard of photosynthesis, either. So memorization will be even easier, as that cluster of synapses already exists.
Taking notes during the lecture fires those same synapses yet again. If a classmate asks a question, another round goes off. Your brain chemistry and structure is actually changing on a cellular level, as you build a bundle of photosynthesis-related synapses that will now endure for weeks, months, or even years.
If you study your notes later, and perhaps read the associated chapter in your textbook, it becomes even stronger. Have a nap or a great night’s sleep immediately after studying, and your dreams fire those synapses a few more times. This is Long Term Potentiation.
So… I’m supposed to put plants near windows, right? I think there was something about watering, too.
Does it work? Fast forward a few decades, after you haven’t thought about photosynthesis in years; perhaps when you’re reading a blog to improve your public speaking skills. Do words like “chlorophyll” or “ATP” come bubbling up out of nowhere, unused since your university biology class?
If so, at some point you successfully used LTP to create a long-term memory, a process called “consolidation.”
You can reverse it, too. Another process, called Long Term Depression, actually tears down long-term memories. No one is sure how or why the brain does this, though it may be to make room for new knowledge, a means for old dogs to learn new tricks.
For example, if you’re of a certain age, you probably used to memorize dozens of phone numbers almost immediately. When a friend changed phones, you almost immediately forgot that number, although it had been easily accessible in your long-term memory for years. Today, you may have forgotten how to memorize phone numbers at all. There’s no need to waste valuable real estate in your brain on such things.
This is called “synaptic plasticity.” Your brain changes—growing, shrinking, becoming smarter, displaying signs of dementia—throughout your life. Despite what you may have been led to believe, not even your IQ is static. It goes up and down depending on how, and how much, you use your brain.
Your brain remains plastic until the day you die, and LTP may well prove one of the most important processes in maintaining healthy plasticity.
Neurons That Fire Together, Wire Together
“Understanding memory is one of the grand challenges of neuroscience,” explains one of the Brain Prize winners, Richard Morris, Professor of Neuroscience at the University of Edinburgh. “I think we all recognize that memory is absolutely fundamental to so many aspects of our daily life [which is why] disorders of memory are greatly feared.”
When you learn those “cheats” to improve your memory—repetition, rhyming, storytelling, and the like—you aren’t thinking about the chemicals involved in the LTP process.
But, according to Morris and his fellow Brain Prize recipients, you need a variety of chemical—calcium, magnesium, and a protein called PSD-95—to fire that synapse, strengthen that memory, and remember the name of your boss’s husband. All the naps and repetition in the world can’t help a mutant mouse, bred to be unable to produce PSD-95, remember how to run a maze. Add that protein, and its memory operates normally.
Your memory may one day be just as easily manipulated.
There are already several working hypotheses built on this research. For example, if you block the formation of something called “dendritic spines,” structures that physically grow and retract in the hypothalamus during the formation of new memories, you might be able to block a memory from being formed. Or, if you increase a specific type of calcium activity in the postsynaptic cell before the memory is formed, which helps prepare synapses for stimulation, you might make memorization easier.