Human Memory III
4-5 Minute Read
Author: Bruce Morgenstern, MD
Purpose
Establish an understanding of the processes of memory and memory formation to assist in promoting student learning so that teaching faculty are better prepared.
Learning Objectives
Appreciate the complexities and unknowns of long-term memory formation.
So, we’ve covered a good bit about human memory in Human Memory I and Human Memory II. But, wait, there’s more! Much to our cumulative chagrin, memory is largely a biological phenomenon that involves protein synthesis, likely some epigenetics, and a concept in neurons referred to as plasticity (rest assured we will touch on that). And that’s merely the formation of long-term memories.
It’s quite logical that the “magic” in memory is not the formation of the memory, as remarkable as that process is, it’s in retrieving the memory. Somehow, whether it’s explicit or implicit memory (you may need to look back at Human Memory II to refresh that business of explicit and implicit memory), the brain needs to sort through its circuits to locate where the memory is stored, and, equally importantly, how it’s stored. Most of us of a certain age can recall the attack on 9/11. How that memory is stored involves a bunch of other memories—what we were doing? Did we lose people close to us? Did we participate in the rescue efforts? Each of those other memories have an impact on how we perceive the event itself. Let’s get into some of the details.
Long-term memory is in part dependent on neuronal plasticity—the ability of synapses to change over time.(1) The cycle is simply thought of as follows:
Some event happens that the brain decides (unknown how) to store. That creates activity in neural circuits, which depend on the ability of the synapse to change, which in turn depend on gene expression and protein synthesis. This leads to growth of the synapse (in some clear context dependent on the circuitry), which creates a new state that can re-enter the cycle, even for the same memory.
The cartoon below (based on graphics from the Dart Neurosciences web site which are based on (1)) demonstrates what happens. On the image on the web site, “induction” has been changed to “learning,” early LTP (long-term potentiation) to “Short-term memory,” and Late LTP to “Long-term memory.” The steps from left to right require repetitive stimulation to persist.
One last cartoon to demonstrate this process of memory formation (from the same sources. It’s actually panel c of the image):
The usual cell processes pertain: a stimulus leads to signal transduction to the nucleus, where gene transcription then leads to protein synthesis, which then leads to a change in the shape and number of synapses (or at least the number of neurotransmitter receptors).
Whew! Time for a break from all this molecular biology? Wait! One last item before we move on.
We recognize that the paper we’ve adapted images from comes from Dart Neuroscience which is vested in the cAMPresponse-element-binding protein (CREB) gene pathways and their role in memory formation and enhancement.(1) We’ll happily stipulate that there are other genes and pathways involved. What’s of interest is that this cartoon offers some molecular explanations for the disordered memory formation and learning issues associated with the syndromes in the rectangular boxes, which are typically associated with some degree in intellectual impairment.
Before you go, let’s return to short term memory for a moment. It’s also called working memory, and the immediate recall of a phone # is a practical example of its use. Those of us of a certain age remember when telephone numbers (land lines) were comprised of 2 letters and 5 digits. Ever wonder why? American psychologist George A. Miller, who was then working for Bell Labs, discovered that the store of short-term memory was 7±2 items – voila!(2) As yet another side, Bell Telephone had a legal monopoly at the time, and Bell Labs did some remarkable things.
Of course, now we have to retain/use 10-digit phone numbers. So, how to we handle the extra digits? Have our brains evolved? [Perhaps in another session we’ll demonstrate that, if anything, our brains have devolved]. Nope, there’s a complementary concept called chunking that allows us to increase working memory capacity. So,
in recalling a ten-digit telephone number, a person could chunk the digits into three groups: first, the area code, then a three-digit chunk, and, last, a four-digit chunk. This method of remembering telephone numbers is far more effective than attempting to remember a string of 10 digits…because we are able to chunk the information into meaningful groups of numbers. This is reflected in some countries’ tendencies to display telephone numbers as several chunks of two to four numbers.(3)■
References
Tully T, Bourtchouladze R, Scott R, Tallman J. Targeting the CREB pathway for memory enhancers. Nat Rev Drug Discov. 2003;2(4):267-277. doi:10.1038/nrd1061
Miller GA. The magical number seven, plus or minus two: Some limits on our capacity for processing information. Psychological Review. 1956;63(2):81-97. doi:10.1037/h0043158
Memory – Wikipedia. Accessed February 10, 2023. https://en.wikipedia.org/wiki/Memory