‘Amnesic Shadow’ Suggests That People Could Actively Repress Memories

What if forgetting something wasn’t always an inconvenience? What if it was just your brain helping you out? It turns out that may be the case, according to new research delving into the depths of human memory.

The interconnectedness of the brain is usually seen as an advantage, a feature that sets humans apart when it comes to cognitive potential. But in some instances, the brain’s quick responses and interconnected pathways can be detrimental to overall mental health, particularly when it comes to painful memories that we’d rather not think about.

A drawing of the hippocampus in the brain made by Camillo Golgi, an Italian physician and early neuroscientist.

Memories in the brain are linked, meaning that one memory can trigger the retrieval of another without any conscious effort. Sometimes this leads to the resurgence of particularly distressing memories.

But researchers at the University of Cambridge have discovered that humans may be able to train themselves to halt the spontaneous retrieval of potentially unpleasant memories.

Previous imaging studies have shown that the brain’s frontal areas have the ability to dampen the activity of the hippocampus, a key part of the brain in memory formation, suppressing memory retrieval. Scientists wanted to look at what happens in the brain after these memories are suppressed.

Here’s Bahar Gholipour reporting with Scientific American:

[The researchers] asked 381 college students to learn pairs of loosely related words. Later, the students were shown one word and asked to recall the other—or to do the opposite and to actively not think about the other word. Sometimes between these tasks they were shown unusual images, such as a peacock standing in a parking lot.

As described in Nature Communications, the researchers found that the participants’ ability to subsequently recall the peacocks and other strange pictures was about 40 percent lower if they had been instructed to suppress memories of words before or after seeing the images, compared with trials in which they had been asked to recall the words.

This finding suggests that controlling memory is possible, and that actively forgetting a particular memory dampens your brain’s capabilities to remember another. The brain, in an effort to forget one certain event, will block recollection of other unrelated events that occurred during the drop is hippocampal activity, a phenomenon known as “amnesic shadow”.

This finding could shed light on why some people’s general memory function decreases after experiencing a trauma event that their brains try to suppress.

But temporary amnesia aside, the ability to suppress memory may be beneficial if we can do it on demand. The researchers are now looking into that possibility by monitoring participants’ brain activity and giving them real-time feedback on decreased hippocampal activity. They hope that by doing this, people can learn to selectively forget the past. This could have real-world benefits when it comes to treating conditions such as post-traumatic stress disorder.