Bauch, E.M.; (2012) Neural correlates of long-term memory: the interplay between encoding and retrieval. Doctoral thesis , UCL (University College London).

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Abstract

Neural correlates of human long-term memory encoding and retrieval have been studied in relative isolation. Memory performance, however, benefits from an overlap between processes engaged at encoding and retrieval. This thesis sought to determine how encoding-retrieval overlap affects neural correlates of memory. Four studies were conducted using electrical brain activity recorded from the scalps of healthy adults. The first experiment addressed whether congruency in mode of presentation across study and test (word or picture) influences encoding-related activity. The findings showed that this was indeed the case, but only for pictures. When a picture was probed with a picture, activity over anterior scalp sites predicted encoding success. When a picture was probed with a word, encoding-related activity was instead maximal over posterior sites. The remaining experiments determined whether the amount of perceptual information contained within a picture affects memory-related activity. Study-test congruency primarily affected encoding-related activity, irrespective of the amount of information that had to be encoded. Retrieval-related activity, by contrast, was instead sensitive to the amount of information contained within a retrieval probe. Analyses in the frequency domain suggested that memory retrieval relies on the reinstatement of neural activity across study and test. Oscillatory power in the theta frequency band (4-8 Hz) over frontal scalp sites at both encoding and retrieval was specific to the encoded amount of pictorial information. Together, the data demonstrate that neural correlates of long-term memory are sensitive to the similarity between processes engaged at study and test. However, study-test overlap may not be a universal organizing principle. Effects of study-test congruency depend on the type of information contained within a study event and test probe, and the type of neural activity that is considered.

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