fMRI exploration of pedagogical benefits of repeated testing: when more is not always better

Introduction: The testing effect refers to superior retention when study is followed by a test rather than followed by another study. Most research to date on why the testing effect occurs has been behavioral, but we employed neuroimaging methods in this study in order to shed light on the underlying processes. Methods: Subjects were scanned while studying, restudying, and taking cued-recall tests of word pairs (with no feedback). We analyzed the BOLD responses by back sorting the encoding and test trials based on whether the subsequent test was correct or incorrect. We compared the subsequent memory patterns in initial study, restudy, and test trials. Results: Overall, brain activity during test trials was a better predictor of later performance than brain activity during restudy trials. For test trials, we separately examined brain regions associated with the retrieval attempt process during successful retrieval and regions associated with the re-encoding process during retrieval in terms of prediction of subsequent memory. Regions associated with retrieval attempts were found to always predict subsequent memory success (the greater the activation, the more likely the correct recall); however, the regions associated with re-encoding would sometimes predict subsequent failure, specifically when subjects had correctly recalled the associated word several times already. Conclusions: These results suggest that whether a testing effect advantage is observed depends on both on the retrieval process and the re-encoding process which follows that retrieval.