Are we able to control memory – and forgetting?

Keeping a Spotless Mind: The neuroscience of "motivated forgetting"

https://www.youtube.com/watch?v=NTQd--o61NQ

Prof. Michael Anderson

This is an interesting lecture by Prof. Michael Anderson who presents his case very clearly.

Prof. Anderson works at Cambridge University.  He believes that memory, like other aspects of cognition and behavior, is something we can control and as such it poses for us problems of control.  Anderson studies the mechanisms that allow us to suppress unwanted memories.  He studies the role of frontal systems of inhibitory control in forgetting processes.

Here are some of the interesting things he says in the:

Is forgetting good or bad?

Every one of us experiences frustration when he can't retrieve things that he is sure he knows, or when he can't remember a significant experience from his past about which he hears from someone else.

But there are many advantages to forgetting.  We tend to forget things that arise negative emotions like fear, shame and guilt.  We forget in order to be able to forgive – forgive ourselves for things we've done and are not proud of, and forgive others.  We forget things that threaten our self esteem.  Sometimes we forget our failings (or at least remember them vaguely, not in detail and not with the same emotional intensity).  This gives us strength to face similar situations and try again.

How do we forget?

The forgetting mechanism that Prof. Anderson suggests in this lecture is related to inhibitory control.  We know the term as part of executive functions.  Inhibition is the suppression of a strong and wrong response for a weak and correct one.  The more automatic a task is, the stronger the inhibition we will need to apply in order to stop it.  Prof.  Anderson gives an example of a cactus plant that falls off a table.  Our automatic reaction is to catch it, but there could be uncomfortable consequences…  The preferred and weak response would be to refrain from catching it and to clean the floor later (cautiously).

This is an example of an inhibition of a motor response.  Anderson argues that inhibitory control also helps us to control memory - to control what we retrieve from memory.

  

Sometimes we see or hear a stimulus that automatically invokes a specific memory.  But we don't always allow that memory to reach consciousness.  Sometimes the memory is irrelevant for our purpose at that moment, and sometimes it is emotionally difficult.  We can stop such memories and not experience them.  How?

In order to study this Anderson and his friends used a simple model of learning word pairs.  Participants in the study learned random word pairs like "picture – scissors"; "handle – flower"; "chimney – dog".  Then they were presented with the first word of each pair, and had to respond with the second word. 

In the second phase of the experiment the researchers divided the word pairs into three groups.

The first word of each pair in the first group was presented in green.  The participants responded with the second word– just like in the first phase of the study.  For example, they saw the word "picture" and responded with "scissors".

The first word of each pair in the second group was presented in red.  The participants were instructed that when they see a red word, they should stop their thoughts about that word's pair and not let it reach consciousness.  For example, they saw the word "handle" and were asked not to think about its pair.

The word pairs of the third group were not presented in this stage at all.

The third phase was a repetition of the first phase.  They presented the first word of each pair of all three groups, and asked the participants to say the second word. 

The green word pairs (like "picture – scissors") were recalled best.  These were trained in both phase one and two.  The word pairs that were not presented in the second phase at all (like "chimney – dog") were less well recalled.  The red word pairs that participants were asked to suppress (not to allow the second word to reach consciousness,  like the pair "handle – flower") were the least well recalled.

This means that we can intentionally forget when we try not to let certain information enter consciousness.  Anderson calls this Suppression Induced Forgetting.

Not all the stimuli we encounter, that can provoke a specific memory, would actually provoke that memory or strengthen it.  It depends on our inner stance or attitude towards that memory.  If we don't want to remember, these stimuli may actually help us to suppress that memory. 

Anderson and his friends found out, that when people suppress memories actively (like when they look at a red word and are asked not to think about its pair), there is a significant inhibition in the activity of the hippocampus in both sides of the brain!  The hippocampus is one of the brain structures that are the most important for memory.  The degree to which the hippocampus is suppressed when people look at a "red" word predicts the degree of forgetting of that word's pair in the third phase of the experiment.

Are we able to inhibit only specific unwanted memories, or is the inhibition more global, also affecting wanted memories?

Apparently, inhibition tends to be global.  Anderson argues that when we suppress an unwanted memory, it is accompanied by an "amnestic shadow".  When we encounter a stimulus that raises an unwanted memory, we suppress not only this specific memory, but also other completely neutral events, that are unrelated to that memory, that happened before and after we encountered that arousing stimulus. 

And thus stimuli that arise unwanted memories can interrupt learning of completely different, neutral things.

And so, following trauma there sometimes is a period of memory loss, even for things that are unrelated to the trauma.  In the past people thought it is related to stress, distractedness and sleep loss.  Anderson adds a fourth cause – suppression of the memory of the traumatic event that also affects other memories.

Not all of us can control memories or inhibit unwanted memories.  Children younger than 10-12, old people, people with anxiety and depression, ADHD, PTSD and brain injury have more difficulty doing it.