Can memories be altered, can bad memories be erased or can our responses to these memories be changed? Researchers from the University of Bologna put these questions to the test using repetitive transcranial magnetic stimulation (rTMS), a non-invasive procedure where nerve cells in the brain are stimulated using magnetic fields.
A memory is defined as “the process in which the mind interprets, stores and retrieves information”. The three stages of memory formation include: sensory register, short-term memory and long-term memory. During the sensory register stage, the brain collects sensory information passively from the environment. In order to then achieve short-term memory, attention is required. Short-term memory occurs when the brain stores information temporarily, possibly for the purpose of manipulating it (like when solving a math exercise). Long-term memory allows the brain to store information for longer periods, ranging from a day to years.
The prefrontal cortex has been implicated in decision making, memory, personality expression, cognitive and social behaviour, and more. It is an essential part of the brain in memory recollection, and this is also where reconsolidation takes place. Reconsolidation, or memory consolidation, is a process that stabilises a memory after it is initially created. However, it is also a period where a memory becomes amenable to modification, and this is the timeframe that the researchers relied on.
In order to test this, 98 participants first learned an aversive memory, combining an unpleasant stimulation with images. The following day, the participants were presented the same stimulus and underwent a rTMS session straight after in order to interfere with brain activity. An electromagnetic coil was placed on the head of the participants and magnetic fields triggered brain activity in specific parts of the brain. In this case, the focus was on the prefrontal cortex.
Meanwhile, the control groups either underwent rTMS in control brain areas (that are not involved in memory reconsolidation) or underwent rTMS without their aversive memory being recalled (so reconsolidation did not occur).
The researchers found that the individuals that had their prefrontal cortex activity inhibited (via rTMS) had a reduced psychological and physical response to the stimuli! They could fully recall the event/memory, but they were not affected by it negatively nor in the same way as the other control participants.
These results are extremely encouraging for reducing responses to traumatic and stressful events in everyday life, but especially in patients with post-traumatic stress disorder (PTSD). PTSD is a psychiatric disorder that is triggered by a terrifying event and is characterised by intense feelings of distress, invasive memories, flashbacks, extreme physical reactions, and more. Although the memories are not removed entirely, their traumatic nature may be diminished or erased, and simply become a memory like any other. The authors have stated that they are looking to focus their next study on altering memory consolidation in individuals with PTSD.
Original source: Borgomaneri, S., Battaglia, S., Garofalo, S., Tortora, F., Avenanti, A., di Peellegrino, G. (July 2020). “State-dependent TMS over Prefrontal Cortex disrupts fear-memory reconsolidation and prevents the return of fear”. Current Biology.