The almond-shaped region of the brain called the amygdala fired hysterically as she entered the dark simulation room. Following this, her heart started beating rapidly and she began to sweat profusely. Nyctophobia, that is the fear of darkness that had gripped her as a child continued through her teenage years. The traumatic episode of being threatened at knife-point during her childhood was most likely the trigger. Not being able to be alone in darkness even as an adult made her further anxious. She finally decided to undergo therapy for the same. Gathering every ounce of courage she had, she took a couple of tiny steps. Before she could think of progressing further, she was called back by her therapist. She stood in the lighted room with her therapist, breathless, and stunned from her endeavor. After about 10 minutes, her therapist made her step into the dark simulation room once again. This time she took a couple of steps extra. She was made to stay there in isolation for around 20 seconds. Her physiological rate of arousal was being constantly monitored by the therapist through the skin conductance device attached to her palm. She was about to scream her lungs out in panic and fear when she was called back again. This continued for about 10 times. Compared to the first few times, when she predicted evil to consume her in darkness, her fear started to vanish, albeit slowly. When she was called for therapy the following day, she could step in and stay inside the darkroom for almost a minute the first attempt itself.
This is a common form of therapy used to alter fear memories. To understand the logic behind it, we need to consider our brain’s predictive mechanism. Based on previous experience, we learn to predict the consequences. This is a possible reason behind her fear of darkness. In the presence of darkness, her brain’s predictive mechanisms prepare the body for flight or fright by activating appropriate physiological responses. Interestingly, there is a property of memory that could be harnessed to alter or modify them with false information. When a previously consolidated long-term memory is activated, as in her first day of therapy when she was asked to step into the darkroom, the memory becomes unstable and labile. At this stage, the process of reconsolidation has to occur once again. Once the memory is activated, the brain predicts the following sequence according to previously learned information. If this matched the originally encoded information, then the original memory gets further strengthened during the secondary consolidation. This is called the ‘testing effect’. In case there is a mismatch in the predicted information and the actually occurring event, a prediction error takes place. Following this, the brain modifies its predictions. Such conditions where the memory is not activated in the exact way it was encoded is known as ‘incomplete reminders’.
When she was repeatedly exposed to the darkroom, her fear started vanishing as her anticipation of some kind of evil lurking in the darkness was debunked. Thus her predictions started to be updated and modified. It is crucial that such modifications occur during the critical period where the memory activated by an incomplete reminder is labile. Once modified, this new memory that darkness, in fact, is not so dangerous will get reconsolidated. More so, the fear component is slowly separated from the original memory, which is indeed seen as reduced activation in the amygdala. It is also important to note that for such therapies to work, there needs to be a moderate level activation of the original memory as in the case of an incomplete reminder. If the activation is extremely weak, it is as good as no activation at all and hence the original memory remains as it is. In case of a strong activation, the memory will only become stronger during reconsolidation. At a neuronal level, during moderate levels of memory activation, the neurons are plastic and are capable of differentiating, forming new connections. Hence this is the perfect window to perform manipulations and alter memories!