It often happens that we wish to forget an event that has left us with an unpleasant, embarrassing, or painful memory.
In fact, a group of neuroscientists from the University of Cambridge, in the United Kingdom, has shown that human beings use two processes to forget: suppression and substitution, and that the brain works in different ways in each case (Benoit and Anderson, 2012).
According to Roland Benoit, these are two different mechanisms that produce forgetting: “the first hinders the memory retrieval process and the second allows unpleasant events to be replaced by others” (2012). In fact, these are two opposing ways in which the brain allows us to volitionally forget unwanted memories.
This study is the first demonstration of two different mechanisms that cause such forgetting: one, by turning “OFF” the memory system and, the other, by providing the memory system with a substitute memory to occupy consciousness.
The researchers used functional magnetic resonance imaging to explore the brain activity of subjects who had learned associations between pairs of words and who then tried to forget them according to one of the two processes, that is, by blocking or substituting them (Benoit and Anderson, 2012).
In the study, a screen was placed where words appeared, and two groups were formed from a total of 36 participating subjects. These subjects encoded pairs of words, such as, for example, snow-Antarctica, beach-Africa, sugar-sweet, etc. First, they were prepared to remember the association and then to forget the second word that made up each pair, trying to block its recall, that is, using the suppression strategy (Benoit and Anderson, 2012).
Secondly, participants picked a new word that replaced part of the pair. For example, beach-diving, sugar-chocolate, snow-cold, while the second words that made up each pair were erased from the screen. Therefore, in this part of the study, subjects were trained not to think of “Africa”, “Antarctica”, “Amazon” by retrieving the substitute word “diving”, “chocolate”, “cold” (Benoit and Anderson, 2012).
The results indicated that each mechanism, substitution and suppression, activates distinct neural circuits. In this sense, when a memory is suppressed, a disturbance of mnemonic processes originates due to the dorsolateral prefrontal cortex, which inhibits the activity of the hippocampus, a brain region that is fundamental for remembering previous events (Benoit, 2012).
In contrast, when some memories are substituted for others, two brain areas are involved, specifically, the prefrontal cortex and the midventrolateral prefrontal cortex, which function to bring certain memories into our consciousness while simultaneously “eliminating” unwanted ones. In this substitution of thoughts, two elements intervene: a substitute memory, which is to be retrieved, and another that is unpleasant to the person.
It should be noted that the two forgetting strategies (supression and substitution) proved equally adequate when it came to getting rid of memories because “these are two mechanisms that help improve mnemonic control of mental association to retrieve memories,” notes Benoit (2012).
Finally, knowing that different processes favor the forgetting of memories can be useful “because now we know that people naturally do better with one mechanism or another” (Benoit, 2012). Therefore, based on these results, treatments for mental health problems related to deficient memory regulation, such as those that occur after suffering a traumatic brain injury, could be developed (Benoit, 2012).