First steps in using machine learning on fMRI data to predict intrusive memories of traumatic film footage.
Bottom Line: While traditional mass univariate regression analysis highlighted an association between brain processing and symptomatology, this is not the same as prediction.Using MVPA and a machine learning classifier, it was possible to predict later intrusive memories across participants with 68% accuracy, and within a participant with 97% accuracy; i.e. the classifier could identify out of multiple scenes those that would later return as an intrusive memory.MVPA opens the possibility of decoding brain activity to reconstruct idiosyncratic cognitive events with relevance to understanding and predicting mental health symptoms.
Affiliation: University Department of Psychiatry, Warneford Hospital, University of Oxford, United Kingdom.Show MeSH
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Mentions: The support vector machine (SVM) classifier was first optimised on the larger of the 2 data sets (Clark et al., submitted for publication; 35 participants). A labelled sequence of Flashback and Potential scene time points in the film was created from the diaries for each individual participant (as each person may have different intrusions). The input features detailed above, reflecting activation across the brain, were extracted from the fMRI data during these Flashback and Potential time points (see Niehaus et al., 2014 for details). The SVM was then trained on this data to learn the patterns for both scene types, using a leave-one-out methodology to provide a test case: for 1 participant brain activation was not included in the training. Based upon the learned patterns of activity from all other participants, the classifier then attempted to identify the film scenes that later induced intrusive memories for the left-out participant. Identification based on brain activation patterns was the checked against the participant's diary entries (see Fig. 2). This leave-one-out ‘cross-validation loop’ was conducted 35 times, each one with a different participant left out of the training set. Results were averaged over the performance of the SVM on the left-out participant.
Affiliation: University Department of Psychiatry, Warneford Hospital, University of Oxford, United Kingdom.