NSF-BSF: Memory modification through concurrent conscious and unconscious stimulation

Our memories are at the heart of our basic human experience. From fondly recollecting childhood events to remembering where we left our keys, memory plays a vital role in every aspect of our lives. It provides us with a sense of identity, preserves what we have learned, and teaches us life lessons that we can apply in the future. However, there is also a dark side to memories. While we rely on our memories to guide our behavior, sometimes the recall of painful memories can be anguishing and rekindle stress. One of the most striking examples of this occurs in post-traumatic stress disorder (PTSD), a devastating condition in which a previous traumatic memory can be disabling, and make it hard to get through the day. Is there a way to help people suffering from PTSD (which affects an estimated 7-8% of Americans) by changing their memories? Psychologists have long debated how and whether memories can be changed, but the answer to this question still remains unknown. However, recent evidence indicates that seemingly stable memories are susceptible to modification. Inspired by neuroscience research showing that at the cellular level, weak stimulation of a synaptic contact between neurons can lead to a decrease in synaptic strength, an intriguing possibility is that weak reminders of past associations paired with novel information could be very effective at modifying or even overriding those older memories. Based on this insight, this project aims to test a novel method for memory modification that involves simultaneous presentation of information both consciously and unconsciously. The rationale for this conjecture is that since unconscious stimulation is 'weak' and hence should activate its neural pathway weakly, this opens up the possibility of modifying the synaptic connections along this pathway. A combined pairing of past information unconsciously (weak activation) and novel information consciously (strong activation) is hypothesized to set up the ideal conditions for modifying past memories.

This project experimentally tests the hypothesis that concurrent conscious presentation of new information with unconscious presentation of older information will facilitate the modification of those older memories. Experiment participants initially learn associations between two presented word stimuli (AB learning). After participants have learned this paired association, they enter the second phase where they will be asked to learn new, modified versions of the original AB pairs, in which 'A' is now associated with a novel stimulus 'C'. In this phase, participants are presented with different visual information to each eye. In one eye, participants consciously view the new AC pairs, while simultaneously being unconsciously presented with the older (AB) information in their other eye. The experiments make use of a continuous flash suppression technique to manipulate which images reach awareness and which do not. This experimental paradigm allows testing of the hypothesis that unconsciously presenting the older AB information to the other eye facilitates AC learning. In order to determine whether the content of the information presented unconsciously has an impact on the final behavioral memory test, participants are asked to recall which information was presented with each A item (either B or C). The behavioral results from these experiments will resolve whether weakly activating old associations in memory enables modifications of those old memories. This research on potential behavioral tools for memory modification has the potential to lead to breakthroughs that could help people unlearn maladaptive behavior and alleviate the stress associated with vivid memories of painful events. Discoveries that could reshape memory will have profound implications for our understanding of memory and also for society.

This project engages joint international activities through the NSF-BSF (National Science Foundation – Israel Binational Science Foundation) collaboration.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.