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