Post by Flora Moujaes
What's the science?
Why do people mentally retrace their steps when they lose their keys? There is evidence that memory recall can be improved by mentally visualising the psychological and physical environment present when the memory was encoded. This technique, called mental context reinstatement, is also commonly used by police when establishing eyewitness memories, as it has been shown to increase the amount of correct information recalled without increasing the number of errors. However, mental context reinstatement is a subtle and dynamic internal process that is very difficult to measure precisely. Neurofeedback may help address this difficulty: fMRI neurofeedback is a method that provides participants with real-time feedback of their own neural responses. Participants can then use this information to learn to modulate their own neural responses. By using neurofeedback to reinforce participants’ use of mental context reinstatement, it may be possible to improve measurement sensitivity. This week in NeuroImage, deBettencourt and colleagues demonstrate for the first time that neurofeedback can be used to show that mental context reinstatement predicts memory performance.
How did they do it?
Researchers explored two hypotheses (1) successful mental context reinstatement enables better retrieval of memories from that context, and worse retrieval of memories unrelated to that context, and (2) neurofeedback is important for obtaining these results as it improves measurement sensitivity.
Hypothesis 1: To explore the first hypothesis, participants were instructed to remember two lists of words. Each of the lists was embedded in a different context by interleaving the words with images from a specific category: faces or scenes. These two categories were chosen as both faces and scenes are known to robustly activate regions of visual cortex in fMRI experiments. The participants were then told to remember the context associated with one of the lists by thinking about the images that had appeared between the words. Finally, the participants were instructed to recall as many words as possible from either the list related to that context, or the list unrelated to the context they had reinstated.
Neurofeedback: To increase the participants’ ability to recall the context, real-time multivariate pattern analysis of fMRI data was used to monitor how well their level of neural activity related to the context they had been instructed to remember. This was then communicated back to participants, creating a positive feedback loop designed to increase participants’ mental context reinstatement. Feedback was communicated visually, as participants began by viewing a blended image that started as 50% face and 50% scene. The more participants’ thought about faces, as evidenced by their real-time neural activity, the more visible the face became in the composite image. Participants were instructed that the scene/face mixture proportion was controlled by their brain activity and would indicate their success at picturing the context.
Hypothesis 2: To explore the second hypothesis, the researchers conducted a second experiment comparing a neurofeedback condition to a non-neurofeedback control condition where instead of getting neurofeedback, participants were simply shown either all of the face images or all of the scene images as a reminder.
What did they find?
Is there a relationship between mental context reinstatement and memory? Higher levels of neural context reinstatement were associated with better recall of words related to that context. High levels of neural context reinstatement were also associated with worse recall of words unrelated to that context, e.g. if the face context was reinstated but participants were then asked to recall words from the scene context. This shows that successful context reinstatement does result in increased memory performance.
Is neurofeedback necessary for this experiment? When participants looked at images of either faces or scenes during the context reinstatement period, there was no relationship between neural activity and memory performance. However, when participants were encouraged to picture the scene or face images during the context reinstatement period using neurofeedback, their level of neural context reinstatement was associated with memory performance. This indicates that neurofeedback makes it easier to identify a link between context reinstatement and recall performance, as it amplifies context reinstatement, improving measurement sensitivity.
What's the impact?
This is the first study to use neurofeedback to demonstrate a clear effect of context reinstatement on memory recall: reinstating the correct context boosts memory performance while reinstating the incorrect context reduces memory performance. This study also suggests that neurofeedback can be a useful tool for characterizing brain-behaviour relationships: neurofeedback is used effectively to boost sensitivity to small fluctuations in context reinstatement by amplifying them and making it easier to identify a relationship between context reinstatement (measured neurally) and behaviour. This study adds to the body of work showing real-time fMRI can reveal insights about cognition, not only through boosting performance, but also by improving measurement sensitivity. It may be especially interesting to go on to develop this technique to provide training for context reinstatement, which could help in treating psychiatric disorders that involve memory impairment, such as addiction and post-traumatic stress disorder.
deBettencourt et al. Neurofeedback helps to reveal a relationship between context reinstatement and memory retrieval. NeuroImage (2019). Access the original scientific publication here.