CogBlog – A Cognitive Psychology Blog

Some time ago, I realized a fundamental truth: that memory was weird. Now, I see that what middle-school-me thought was “weird” is more complicated than I ever could’ve imagined.

It was back in 2017 when I first learned that memory was a bit like a slot machine: you never knew what you’d end up with—or rather, you never knew what you’d be left with, after having had multiple strokes. I remember my trip to that rehabilitation facility in Maryland briefly, but the important parts are clear: I was with my parents and my brother. We had come to visit my uncle, who’d undergone two major strokes and countless minor ones. The big ones had been less than a year apart. The first stroke had left him weak yet intact, but the second one had taken things from him. The second stroke had taken his mobility, his memory, and his speech fluency. Years and years ago, I remember this uncle of mine before he had become hindered by his health and subsequent cognitive impairments. I don’t have many memories of my uncle, but one thing I remember being in complete awe of was that he was the only person in the world I knew who could make a seven-letter-word in Scrabble. But now, he could barely say seven words, and my uncle, this fragile man in a wheelchair, was nearly unrecognizable.

Seeing my uncle like this was disheartening but spending time with him was eye-opening. I didn’t say much, and was all too eager to simply say my hellos and spectate. The nurse wheeled him into a room so he could sit with us, and then promptly took off. My dad, eyes heavy, took the first step and said the first words. “Brother, how are you feeling today?” is the closest approximation I can recall—their conversation was in Urdu. My uncle took his time to respond, glassy-eyed with stuttering lips, but he slowly pulled out a haphazard response resembling “by Allah’s grace, I am fine.” My dad then proceeded to ask more effortful questions, such as “do you remember me?” Or “do you remember your kids?” Or “this is my son, wife, and daughter, do you remember them?” My uncle just stared at my dad as he asked these things, eyes faraway with an uncertain smile as he replied in a hoarse voice “Only you, no one else.” A beat of silence passed, and then my brother stepped forward. “Tayabbu, I heard you liked to write so I brought you a notebook and pen,” my brother said, then gently handed said items to my uncle, who muttered a shaky “thank you” before opening the notebook, uncapping the pen, and attempting to write. He could not. His hand shook uncontrollably, and he was not able to write out a single word, leaving instead only a squiggly, long line slashed across the lined page.

He remembered no one from the past twenty years of his life. He could barely speak and could no longer write. From stories my aunt told me, he also forgot how to use the bathroom and swallow food.

So how is it that, as my family began reciting prayers, my uncle, too, remembered every single one? How is it that my uncle, who forgot so much, could barely speak, could no longer write, and could not perform daily functions, somehow remembered litanies of Arabic scripture? At fifteen, I chalked it up to God’s miracles, and, while even now I don’t doubt God’s role, I also know that what happened to my uncle can also be explained using cognitive psychology. My uncle’s formal diagnosis was vascular dementia, or vascular cognitive impairment (VCI). For my uncle, vascular dementia was an aftereffect of multiple minor strokes. In a stroke, the brain’s blood vessels are blocked, leading to brain damage and changes in how the brain functions. Vascular dementia aftereffects can range from mild to severe, depending on how badly blood vessels are damaged and where within the brain they ruptured.

Using the umbrella of my uncle’s experiences as context, I want to explore memory—specifically long-term memory, and, if we want to get even more specific, long-term semantic memory. The specifics matter here, because “memory” is a very broad term. There are many different stages of memory, and there are many different types of memories. We will discuss the memory stages shortly, but first, I want to briefly highlight the three main areas of long-term memory: episodic, procedural, and semantic. Episodic memory is contextual, everyday memory. We use episodic memory to recall life events or autobiographical information. Examples of episodic memory include remembering what you ate last night or recalling the events of your high school graduation. Flashbulb memories are a particularly interesting branch of episodic memory, encompassing our emotionally-charged memories. Episodic memories are subjective and biographical, and they are explicit memories, meaning they have to be consciously recalled. Procedural memory is about skills or “procedures,” and encompasses how to complete tasks. Procedural memories are implicit, meaning they are retrieved subconsciously, or automatically. An example of procedural memory would be in how to ride a bike or brush your teeth—you don’t think about how to do these tasks, you just do them. Semantic memory is the memory of acquired knowledge—memorized facts or information. An example of semantic memory would be remembering the capital of Cuba. Semantic memories don’t require context, making them objective. Like episodic memories, semantic memories are also explicit and require conscious recall.

Thinking back to my uncle’s post-stroke condition now knowing these types of memories, it’s clear now that both his episodic and procedural memories had been damaged. In not being able to remember the past twenty years of his life, he exhibited episodic memory decline, and in being unable to perform daily tasks such as swallowing or using the bathroom, he exhibited procedural memory decline. I even spoke with his doctor recently, who is a family friend, and she confirmed this. She also confirmed my final hunch: that his miraculous memory of all those Arabic prayers was his semantic memory, and that it was, for the most part, still intact. Upon realizing this, I got very, very curious about how semantic memory worked—how it was organized, and what the neural mechanisms (fancy brain stuff) were. And honestly, what I found is that when people say, “it’s all just semantics,” they probably don’t realize how right they are.

The first, perhaps most important thing to note is that our long-term memory is organized semantically. The brain groups together similar concepts based on their “semantics,” or meaning. In the realm of cognitive psychology, semantic memory is both decontextualized knowledge and meaning-based information. The concepts and ideas we already have stored in our minds are decontextualized knowledge that fuels our top-down processes, and the meaning-based characteristics we take in from our environment fuel our bottom-up processes. Those are a lot of big words. Let’s take a step back for a second. A top-down process is basically just how we use prior knowledge to interpret surroundings, and a bottom-up process is how we use new sensory information to form an idea or interpretation. These two processes usually work together, and simultaneously. All semantic memory is meaning-based. In memory models, before information can be moved into long-term memory, it undergoes stages. I told you we would be talking about those. Atkinson and Shiffrin’s Modal Model of memory, for example, mentions sensory memory, short-term memory, and then finally, long-term memory. Sensory memory is when we take in information from the environment, and most of it is lost immediately if we ignore it. What we do pay attention to goes to short-term memory, where it is reviewed and processed if we keep paying attention to it. Finally, once the information has been rehearsed and processed enough, it’s transferred into long-term memory where it is filed into a semantically relevant place. Semantic memories go through a very rigorous encoding process before reaching long-term memory, because it takes more effort to remember things based on their meaning. This meaningful processing is called deep processing. Once semantic information is deeply processed, it’s transferred into long-term memory storage—which is stored all over the brain. While information is organized semantically in the brain, there is no specific region for semantic memory, so it’s kind of all over the place. Additionally, semantic memory in our brain can almost be thought of as a web of concepts and categories. In cognitive psychology, categories are groups of objects with things in common, and concepts are our mental representations of those objects.

However, just because semantic memory is stored everywhere, doesn’t mean there aren’t specific brain regions worth mentioning. Semantic memory formulation relies primarily on three regions: the frontal cortex, the temporal cortex, and the hippocampus. The frontal cortex is used for executive functions, like attention and memory formation. The temporal cortex is responsible for pattern recognition and helps us assign meaning to visual and auditory stimuli. If “assigning meaning” sounds familiar at all, it’s because this has to do with deeply processing something semantically! This is what the temporal cortex helps us do, along with creating long-term memories. As for the hippocampus, researchers wondered if the hippocampus was as important for semantic memory as it was for episodic memory for a long time. The hippocampus is a brain region known for processing memory.

 In a paper published by Duff and colleagues, the semantic memory and hippocampus link is explored. The research on Patient HM’s memory loss was a critical point in cognitive memory studies, and in part, the data showed that, even with a damaged hippocampus, new semantic learning was possible. However, when looking over this famous case, researchers noted there was no control group, and that only baseline levels of semantic learning were detected—that is, semantic memory levels were nowhere near optimal. Researchers now agree that for semantic memory to work properly and effectively, it requires a functioning, intact hippocampus.

Another thing that researchers agree on is that semantic memory overlaps with episodic memory. A mundane example of this would be state-dependent memory when studying: the semantic study material can sometimes be remembered better when the episodic context of encoding (studying) and retrieval (test) is the same. Both episodic and semantic memories are “remembered better” due to a hippocampal process called consolidation. Consolidation is when memories are strengthened by repeated exposure and retrieval on a neural level. When it comes to neural basis, semantic memory needs the hippocampus at every stage: from sensory to short-term, to processing, and then finally, to storage. Although semantic and episodic memories function differently and are stored differently, they overlap quite a bit, and both need the hippocampus!

As we now know, certain areas, such as the frontal and temporal cortexes and the hippocampus, are especially important for semantic memory. Part of why I chose to explore semantic memory instead of episodic or procedural memory was because, in the case of my uncle, that was the only type of memory that he had left that remained somewhat intact. Maybe my uncle remembered the Arabic prayers because those semantic memories were stored in one brain region while his strokes affected another. Maybe it was a miracle after all. Maybe, like with HM, his recollection of these Arabic prayers still only represented a baseline level of semantic memory. Maybe he remembered the Arabic prayers because of how often he read them throughout his life, and how strong the consolidation had made those memories due to the repetition. Or maybe all these things are true because memory is weird. Memory is tricky. Memory is a knot made of many different strings, and the more you twist it, the more likely it is that some pieces will tighten while others loosen.

References:

Duff, M. C., Covington, N. V., Hilverman, C., & Cohen, N. J. (1AD, January 1). Semantic memory and the hippocampus: Revisiting, reaffirming, and extending the reach of their critical relationship. Frontiers. Retrieved April 27, 2022, from https://www.frontiersin.org/articles/10.3389/fnhum.2019.00471/full#h7

Vascular Dementia. Alzheimer’s Disease and Dementia. (n.d.). Retrieved April 27, 2022, from https://www.alz.org/alzheimers-dementia/what-is-dementia/types-of-dementia/vascular-dementia

SpinalCord.com. (2020, November 4). Frontal lobe: Function, Location, and Structure. Frontal Lobe: Function, Location, and Structure. Retrieved April 27, 2022, from https://www.spinalcord.com/frontal-lobe

Perera, A. (2020, December 15). How Semantic Memory Works. Semantic Memory: Definition & Examples | Simply Psychology. Retrieved April 27, 2022, from https://www.simplypsychology.org/semantic-memory.html#vs-episodic

Anthony Metivier. (2022, February 7). Semantic memory: An example-driven definition and how to improve it. Magnetic Memory Method – How to Memorize With A Memory Palace. Retrieved April 27, 2022, from https://www.magneticmemorymethod.com/semantic-memory/#important

Renoult, L., Irish, M., Moscovitch, M., & Rugg, M. (2019, October 28). From Knowing to Remembering: the Semantic-Episodic Distinction. Trends in Cognitive Sciences. Retrieved April 27, 2022, from https://www.cell.com/trends/cognitive-sciences/fulltext/S1364-6613(19)30232-3

Hodges, J. R., & Patterson, K. (1999, September 7). Semantic Memory Disorders. Trends in Cognitive Sciences. Retrieved April 27, 2022, from https://www.sciencedirect.com/science/article/pii/S136466139701022X

McBride, D. M. (2022). Cognitive Psychology: Theory, Process, and Methodology. SAGE PUBLICATIONS.

Heaning, E. (2022, January 13). Henry Gustav Molaison. Henry Gustav Molaison (Patient H.M.) – Simply Psychology. Retrieved April 27, 2022, from https://www.simplypsychology.org/henry-molaison-patient-hm.html#:~:text=Henry%20Gustav%20Molaison%20(often%20referred,result%20of%20his%20surgery%2C%20H.

Perera, A. (2020, October 26). Implicit and explicit memory. Implicit and Explicit Memory | Simply Psychology. Retrieved May 11, 2022, from https://www.simplypsychology.org/implicit-versus-explicit-memory.html

Zimmermann, K. A. (2014, February 22). Procedural memory: Definition and examples. LiveScience. Retrieved May 11, 2022, from https://www.livescience.com/43595-procedural-memory.html

O’Shea, G., & Howes, M. (2014). Flashbulb memory. Flashbulb Memory – An Overview | ScienceDirect Topics. Retrieved May 11, 2022, from https://www.sciencedirect.com/topics/neuroscience/flashbulb-memory