The First Kiss – A Story of Memory

Can I preserve my memories from decaying over time, much like digital photographs?

Try to remember your first ever kiss. There is a good chance you are going to remember the event like it happened only yesterday, irrespective of how long ago it happened. There is a good chance you have a smile on your face now. But there is also a good chance that you are misremembering the finer details of the event – like the color of your partner’s shirt, or whether it was a rainy day and so on. Before you start feeling confused or guilty for not remembering your first kiss accurately, please be advised that human memory was never meant to be an accurate representation of the original event.

The human brain has a limited information storage capacity even though humans have the largest brain size relative to body mass among mammals and new memories are encoded (formed) continuously throughout our life span. In order to make efficient use of the available brain storage, memories are prioritized based on a variety of factors such as its strength, emotional content, novelty and so on, and storage is allocated through the process of “memory consolidation”. Most of this process happens without any conscious effort. The past couple of decades of research seem to point towards a complex array of factors that might affect memory consolidation, sleep and stress being some of the important ones ^{1, 2}.

Then there is “memory retrieval”, which, as the name suggests, is the process of retrieving a memory from the database. A profound effect of memory retrieval is observed during nostalgic experiences. Imagine going back to your high school for your 20^th year reunion. Now, suppose you reach the school earlier than the others and hence start wandering about the school premises. You start recollecting flashes of memory from incidents that happened years ago. Memories you would have never thought you would remember decades later. The retrieval of those memories is possible because of the combination of external stimuli which formed essential pieces of the original memories at the time of their creation.

Memories are not consolidated as discrete events in space and time. Instead, they have complex structures with references to various labels associated with the memory such as the spatial environment of the scene-how it looks, how it smells, how noisy it is and the emotional content of the scene-the people and feelings involved, time of the day and so on ³.

Now comes the tricky process called “memory re-consolidation”. So, let us go back to the first kiss anecdote. You retrieve this special memory from years ago. Somehow, this particular memory comforts you and makes you feel stupid at the same time. Then you get distracted by the buzz of your phone and move on to other thoughts. But unknown to your consciousness, in the middle portion of your brain, closer to the temple of your head, the “medial temporal lobe”, is actively working on restoring the memory of your first kiss for future retrieval, almost as if the memory had just been encoded. Yes, this is essential to the survival of the memory. Why is this tricky? Because the memory is vulnerable to interference prior to consolidation and re-consolidation ⁴.

Think of it this way, each time we open a Word Document and make any changes, we hit the save button right? The difference here is that the changes in the memory are not necessarily voluntary and the save button is hit unconsciously. So regardless of how old the memory of an event is and how accurate you think it is, it can get slightly modified each time you remember it. Hence, the trustworthiness of an individual’s memory is questionable, especially when it can impact the society in unexpected ways (think “Eyewitness memory”) ⁵.

One of the pioneering works in the field of re-consolidation was published by a group of researchers looking at how animals failed to associate fear with a previously learned sound (“Pavlovian Conditioning”) when the reconsolidation of the fear memory was pharmacologically prevented. That is, they gave the animals a certain type of protein-blocking pill that made it less likely for the animal to reconsolidate the fear associated with the sound ⁶.

Newer studies have tried to exploit this feature of memory to extinguish fear and traumatic memories in humans. One study that is worth mentioning took place in Amsterdam, where a group of participants with Arachnophobia (a fear of spiders) were physically exposed to a spider (tarantula, to be precise). This evoked a strong fear memory response. They were given a pill following this exposure to block the process of fear memory re-consolidation. Over a period of time, they ended up being much less arachnophobic and could even touch the spider ⁷.

This article might remind some of you of the 2004 movie, “Eternal Sunshine of the Spotless Mind” – a sci-fi loosely based on the above discussed model of memory. The plot of the movie goes along the lines of erasing memories of a relationship post break-up. A decade and a half since the release of this fictional movie, we are closer than ever to realizing the concept of scientifically editing human memories. So yes, there might be technology developed during my lifetime that will make it possible to preserve memories from decaying over time. But as with all technology, we should aim to use it judiciously and ethically because millions of years of evolution points toward forgetting as being a useful friend.

REFERENCES:

1. Stickgold, R., & Walker, M. P. (2007). Sleep-dependent memory consolidation and reconsolidation. Sleep Medicine, 8(4), 331–43.
2. Wolf, O. T. (2009). Stress and memory in humans: twelve years of progress? Brain Research, 1293, 142-154.
3. Rubin, D. C. (2006). The Basic-Systems Model of Episodic Memory. Perspectives on Psychological Science, 1(4), 277-311.
4. Nader, K., & Hardt, O. (2009). A single standard for memory: the case for reconsolidation. Nature Reviews Neuroscience, 10(3), 224-234.
5. MacLeod, M. D. (2002). Retrieval‐induced forgetting in eyewitness memory: forgetting as a consequence of remembering. Applied Cognitive Psychology, 16(2), 135-149.
6. Nader, K., Schafe, G. E., & Le Doux, J. E. (2000). Fear Memories Require Protein Synthesis In The Amygdala For Reconsolidation After Retrieval. Nature, 406(6797), 722–726.
7. Soeter, M., & Kindt, M. (2015). An Abrupt Transformation of Phobic Behavior After a Post-Retrieval Amnesic Agent. Biological Psychiatry, 78(12), 880-886.

Written by Surya Rajan Selvam

Research Technologist at University of Louisville Dept. of Psychology and Dept. of Neurosurgery

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