By Dr. Pablo Barrecheguren (@pjbarrecheguren)
We tend to think of our intellectual capacities as single chunks and yet abilities such as memory are rather a structure made up of different compartments. All of them are interconnected but at the same time separate.
Proof of this are the diseases that affect memory, as is the case with Alzheimer’s; Dr. Alzheimer himself even discovered that patients lost some memories before others. One of his patients, Auguste Deter, was the first person to be diagnosed with the disease; Auguste could say the names of the months without making a single mistake but was unable to answer if asked what the eleventh month of the year was. For artists with Alzheimer’s disease, patients are often able to continue playing an instrument or paint even if they have trouble remembering their own full name.
Kleine-Levin syndrome is yet another example. This syndrome is characterized by episodic mood changes, hypersomnia (12-21 hours of sleep a day) and memory problems, specifically in working memory (which is responsible for temporarily holding information while we are completing a task).
When talking about memory in general, we usually refer to long-term memory, which can hold information for days or even decades, and which is divided into two main types:
- Implicit memory: the memory we use to perform certain actions such as tying our shoelaces, dancing or riding a bike.
- Declarative memory: the conscious recollection of factual information; this type of memory can be further subdivided into:
- Semantic memory is the knowledge gained through study (e.g., the metabolic pathway of the citric acid cycle, the capital cities of Europe or knowing that Scotland’s climate is rainy even though we have never been there).
- Episodic memory is autobiographical (e.g., knowing that it rains in Scotland because it did on a vacation we spent there).
These divisions into subtypes of memory are not a whim but functional differences have been seen between them. For example, we know that human beings probably store almost all our life experiences (episodic memory). The problem is that storing information and recalling it are two very different tasks.
The study of the brain indicates that the temporal lobes are vital for memory storage and in fact, it is possible to evoke memories artificially: if electrodes are applied to these brain areas and are then stimulated, patients in some cases can remember completely forgotten memories to the point that they can even have hallucinations in which they relive past experiences.
This phenomenon also occurs in patients who develop problems in these areas. It is documented in the case of an old Irish woman who one day woke up listening to songs from her childhood (songs she had forgotten decades ago). The music continued for a few months in her head and did not go away until she recovered from a small thrombosis in part of her right temporal lobe. When talking about memory, we must bear in mind that it is a multi-systemic process that also involves brain regions such as the hippocampus (specifically important for spatial memory) or the frontal lobes (very important in the retrieval of stored memories).
A little forgetfulness
A very interesting facet of the memory world is the opposite of neurodegenerative diseases and forgetfulness. There are people with mnemonic abilities who actually sound like superheroes. The clearest cases, although extremely infrequent, are people who have ‘highly superior autobiographical memory’ (HSAM). Individuals with HSAM are able to recall, with considerable accuracy, much of their lives in incredible detail.
We could, for example, ask them what they were doing twenty years ago at 9 p.m. and they would tell us what they were cooking at that moment, the clothes they were wearing, what the kitchen smelled like and everything they had done during that day. The downside is that these people are literally unable to forget, so it is recommended that they lead as quiet lives as possible because the inability to forget makes it very difficult for them to overcome emotional trauma. For example, one piece of medical advice is not to join the military.
So, ironically, a little forgetfulness is the way to a trouble-free memory.
- Aslihan Selimbeyoglu and Josef Parvizi. (2010). Electrical stimulation of the human brain: perceptual and behavioral phenomena reported in the old and new literature. Frontiers in Neurology. Volume 4, Article 46.
- Draaisma, D. (2012). Alzheimer, supongo. Editorial Ariel.
- Joshua Jacobs, Bradley Lega, and Christopher Anderson. (2012). Explaining How Brain Stimulation Can Evoke Memories. Journal of Cognitive Neuroscience. 24:3, pp. 553–563.
- Miglis, M. G., & Guilleminault, C. (2014). Kleine-Levin syndrome: A review. Nature and Science of Sleep, 6, 19–26.
- Nanthia Suthana, & Itzhak Fried (2014). Deep Brain Stimulation for Enhancement of Learning and Memory. Neuroimage, 85(0 3): 996–1002
- Richard W. Murrow. (2014). Penfield’s prediction: a mechanism for deep brain stimulation. Frontiers in Neurology. Volume 5, Article 213.
- Sacks, O. (2002). Reminiscencias. El hombre que confundió a su mujer con un sombrero. Editorial Anagrama.
- Schacter, D. (2001). Los siete pecados de la memoria: como olvida y recuerda la mente. Editorial Ariel.
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