Everything About Memory

Pablo Barrecheguren, PhD in Biomedicine, explains the structure of memory and tells us what each type of memory is used for.

We tend to think of our intellectual abilities as single, unified blocks; however, skills such as memory are more like a structure made up of different departments. They are all interconnected yet separate at the same time.

Evidence of this comes from diseases that affect memory, such as Alzheimer’s disease: even Dr. Alzheimer himself realized that patients lost some memories before others, since his first diagnosed patient, Auguste Deter, could name the months without making a single mistake but was unable to answer when asked which month was the eleventh month of the year.

Similarly, in the case of artists with Alzheimer’s disease, patients are often able to continue playing an instrument or painting, even though they may struggle to remember their own full name.

Another example is Kleine-Levin syndrome, a syndrome characterized by episodes during which patients experience behavioral changes, sleep 12–21 hours a day, and have memory problems, specifically involving working memory (which is responsible for temporarily storing information while we are performing a task).

Long-term memory

But when we talk about memory in general, we usually mean long-term memory, which stores information for days or even decades and is divided into two groups:

1. Implicit memory, which we use to perform actions such as tying our shoelaces, dancing, or riding a bicycle.
2. Declarative memory, which encompasses all our conscious knowledge and is further divided into two sections:
   1. Semantic memory, which includes everything we know through study, from the metabolic pathway of the Krebs cycle and the capitals of Europe to knowing that the climate in Scotland is rainy even though we have never been there.
   2. Episodic memory consists of our personal memories. For example, if we know that it rains in Scotland because we remember that it rained when we went on vacation, that is an episodic memory.

These divisions into memory subtypes are not arbitrary; functional differences have been observed among them.

For example, we know that human beings probably memorize almost all of their experiences throughout their lives (episodic memory). The problem is that memorizing information and remembering it are two very different tasks…

A multisystem process

Studies of the brain indicate that the temporal lobes are very important for storing memories, and it is in fact possible to artificially trigger reminiscences: if we place electrodes in these areas of a patient’s brain and stimulate them, patients in some cases remember memories they had completely forgotten, to the point that they may even experience full hallucinations in which they relive moments from their past.

This phenomenon also occurs in patients who develop problems in these areas. The case of an elderly Irish woman who woke up one day hearing songs from her childhood (songs she had forgotten decades earlier) has been documented.

The music continued in her head for months and did not stop until she recovered from a small thrombosis in her right temporal lobe.

When discussing memory, it is important to bear in mind that it is a multisystem process that also involves brain areas such as the hippocampus (especially important for spatial memory) and the frontal lobes (very important for retrieving stored memories).

A little forgetting

It is very interesting that in the world of memory there is an opposite to neurodegenerative diseases and forgetting. Some people have mnemonic abilities that make them seem like superheroes.

The clearest cases, although numerically very rare, are people who have ‘highly superior autobiographical memory‘ (HSAM, from the English highly superior autobiographical memory). People with this type of memory are able to remember practically their entire lives in extraordinary detail.

For example, we could ask them what they were doing twenty years ago at nine o’clock at night, and they would tell us what they were cooking at that moment, what clothes they were wearing, what the kitchen smelled like, and everything they had done that day.

The drawback is that these people are literally unable to forget, so they are advised to lead calm lives whenever possible, since their inability to forget makes it very difficult for them to overcome emotional trauma.

For example, one piece of medical advice is not to enlist in the military. So, ironically, the path to a trouble-free memory involves having a little forgetfulness.

References

• 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: cómo olvida y recuerda la mente. Editorial Ariel.

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