Jing Yit, Pua
Universiti Sains Malaysia
“If you had the chance to erase the worst, the most painful memory of your life, would you?”
I remember watching a science fiction film, Men in Black, and being stunned by their use of a futuristic neurotechnology instrument—memory-erasing neuralyzer. In the movie, memories were deleted to keep alien activities an untold secret. I wonder, what if one day we could selectively edit the memory to reduce the pain or to protect someone? Or clinically, to treat post-traumatic stress disorder (PTSD)?
The discovery of synaptic changes using invertebrate animal models revealed the possibility to modify behavioral expression and neural instantiation of unique memories. A similar technique has not been applied to higher animals, as the alteration of synaptic plasticity is not safe and the complexity of memories in higher animals is elusive. However, after decades of study, neuroscientists and psychologists have finally created some novel approaches to editing human memories with the aim of reducing the emotional effects of PTSD, reducing the uncontrollable cravings led by addictions, and even improving education. Of note, although Kandel’s asserted that there is a considerable promising approach using the optogenetics method to edit the emotional memories, this is almost currently impossible for clinical use, as the approach is too invasive.
Most current research focuses on two types of memory representation:
(1) episodic memory (mediated by the hippocampus)
(2) defensive responses (mediated by the amygdala).
The memory editing strategies are thought to operate by modifying either at initial memory storage (consolidation) or its re-storage after retrieval (re-storage) (reconsolidation).
Consolidating memory editing techniques
Consolidating memory editing technique was first described in 2000. The memory editing was done by administering amnestic drugs to animal models after learning, proved that the drugs stopped the synaptic changes that were needed for memory consolidation and forgetting of the recently encoded memories. However, amnestic drugs are generally not safe for humans. Another recent study by Cain (2012) showed endogenous neurohormonal changes could alter the status of memory consolidation, in particular, emotional events. This provided a great promise for consolidating memory editing techniques for humans. As the stress hormones evoked by PTSD stimulate the memory consolidation of traumatic events, this notion has shed light on memory editing by controlling the expression of stress hormones. Thus, drugs that are safe for human use such as adrenaline, glucocorticoids and propranolol could reduce the stress hormones evoked and in turn, reduce memory consolidation. The study also showed that the administration of glucocorticoids after exposure therapy for PTSD produced a short-term benefit. Interestingly, TMR (targeted memory reactivation) modifies memory reactivation found to affect the strength of memory consolidation. Nonetheless, whether TMR edits the original threat memory or produces a competing safe memory remains controversial.
Re-consolidating memory editing techniques
As for the Re-consolidating memory editing technique, it is an idea that one could essentially delete the previously consolidated threat memories, at least as defensive responses. To our knowledge, the only research that has shown a physiological blockade of episodic memory reconsolidation in humans is by electroconvulsive shock therapy. Besides, extinction training during memory reconsolidation showed the prevention of the return of defensive responses for at least a year. Reactivation of the target memory prior to disrupting memory manipulations or distracting games has shown some effectiveness in the treatment of PTSD. Recently, exposure-therapy has been found useful in memory editing. The aim of all exposure-therapy strategies is to reduce the emotional pain associated with a traumatic memory by exposing the traumatic memory to it regularly and thereby emotionally processing it. Although targeting human memory reconsolidation appears as modifying instead of erasing the memories, these findings hold a great promise for memory editing in clinical application.
Memory editing is an extremely complex and complicated science (aka rocket science), yet we only understood a little about how these methods can be applied most efficiently, most safe to clinical treatments at this time. Despite the fact that existing attempts to integrate memory editing into clinical treatments have had mixed results, there is reason to be optimistic. In total, the rapid advancement of neurotechnology indicates that memory-editing techniques could have promising applications in the future.