How the brain compartmentalizes memories with a circuit
Have you ever contemplated the differences between remembering a house address compared to studying for an exam? Or, are you surprised that you have memories of going to the playground with your Kindergarten class? The variety in what we, humans, can remember is tied to memory storage, and therefore, the three-part process of encoding (absorbing information), storing (holding on), and recalling (5).
There are two primary memory types: long-term memory and short-term memory (2). Long-term memories are memories that can be recalled more than twenty-four hours after an event, whereas short-term memories last up to a couple of hours, at most, a day (7). Long-term memory and short-term memory differ in two fundamental ways; short-term memory results in the ultimate “temporal decay” (when attention is moved away from what needed to be remembered) and long-term memory is the continual retention of general, intra-life memories (7).
In 1968, Richard Atkinson and Richard Shiffrin developed a modal memory model which determined three categories through which information passes and is stored (1). First, the sensory register (information is perceived for a few seconds with the five senses), then, the short-term memory, and lastly, the long-term memory (1). This model demonstrates the “journey” of memories, allowing scientists to deduce where memories are stored, yet discounts the transfer of information to long-term memory, believing that rehearsal is the sole method.
Learning and memory require the formation of new neural networks in the brain. Neurons are “information messengers” which utilize chemical and electrical signals to transmit information throughout the brain (11). On this principle, synaptic plasticity is created, forming and strengthening a junction between neurons, forming a neural network and more permanent memory (8).
In order to understand the storage processes between long-term and short-term memory, let’s create a scenario: you are reading a CHASM article about memory, and hope to remember it in order to tell your friends the title’s connection to the actual process.
The scientific community believes that memory is stored as organized synaptic connections between neurons. The neurons that fire, or send electrical impulses, wire to make a bridge in order to remember––memories can be thought of as a cluster of cells that encode a memory (3). As you encode the article title, the connection of neurons continues from the prefrontal cortex (in the front of the brain) to the hippocampus(9). The hippocampus is found in the brain’s temporal lobe and plays the primary role in short-term to long-term memory conversion (9). Neuron connections strengthen and re-wire by synapses stabilizing and wiring in the hippocampus, which completes short-term memory. Short-term memories are initially formed and stored simultaneously with the prefrontal cortex and hippocampus, where at most, they last up to a day (9).
In order to convert a short-term memory to long-term memory, synapses continue to stabilize, rearrange, and neural connections progress from the hippocampus to the neocortex (2). The neocortex is the largest component of the cerebral cortex (the outermost layer of the brain) and is involved in complex functions relating to sensory perception, spatial reasoning, consciousness, motor commands, and language (2). Based on a Massachusetts Institute of Technology (MIT) neuroscience study, the RIKEN-MIT lab theorizes that a circuit between the prefrontal cortex and hippocampus is highly active during memory (10). As time passes from memory encoding, it is likely that there is a shift in the power of the prefrontal cortex and the hippocampus, and memory is recalled when a circuit is engaged, regardless of the storage location (10).
The human brain is not a fully understood topic. As scientists continue to research and theories become known facts, the understanding of memory storage will play a large role in the development of memory-loss drugs, and simply put, the understanding of how we remember the world around us.
Bibliography
- Atkinson. (2021). Atkinson & Shiffrin’s Modal Model of Memory – Video & Lesson Transcript | Study.com. Study.com. Retrieved from https://study.com/academy/lesson/atkinson-shiffrins-modal-model-of-memory.html
- Cowan, N. (2008). Chapter 20 What are the differences between long-term, short-term, and working memory? Progress in Brain Research, 323–338. Retrieved from https://doi.org/10.1016/s0079-6123(07)00020-9
- Gallagher, J. (2017, April 7). Rules of memory “beautifully” rewritten. BBC News; BBC News. Retrieved from https://www.bbc.com/news/health-39518580
- hippocampus [Operative Neurosurgery]. (2017). Operativeneurosurgery.com. Retrieved from https://operativeneurosurgery.com/doku.php?id=hippocampus
- How Memory Works. (2015). Harvard.edu. Retrieved from https://bokcenter.harvard.edu/how-memory-works
- https://www.facebook.com/verywell. (2022). Types of Neurons: Parts, Structure, and Function. Verywell Health. https://www.verywellhealth.com/types-of-neurons-5201172
- Jarrett, C. (2021, April 7). A complete beginner’s guide to human memory. Sciencefocus.com; BBC Science Focus Magazine. Retrieved from https://www.sciencefocus.com/the-human-body/memory/
- Kennedy, M. B. (2013). Synaptic Signaling in Learning and Memory. Cold Spring Harbor Perspectives in Biology, 8(2), a016824. Retrieved from https://doi.org/10.1101/cshperspect.a016824
- Personal Interview with Dr. Janine Kwapis, April 7, 2022.
- Trafton, A. (2017, April). Neuroscientists identify brain circuit necessary for memory formation. MIT News | Massachusetts Institute of Technology. Retrieved from https://news.mit.edu/2017/neuroscientists-identify-brain-circuit-necessary-memory-formation-0406
- Where are memories stored in the brain? (2016, December 2). Uq.edu.au. Retrieved from https://qbi.uq.edu.au/brain-basics/memory/where-are-memories-stored#:~:text=There%20are%20three%20areas%20of,neo%2Dcortex%20and%20the%20amygdala.