Neural correlates of episodic memory: associative memory and confidence drive hippocampus activations

The present study used a study-test recognition memory task to examine the brain regions engaged in episodic and associative memory processes. Participants evaluated on a six-point rating scale how confident they were on whether or not an item was presented in a previous study phase. Neural activations for high- and low-confidence decisions were examined in old and new items at two levels of between-item-associations. Items had different amounts of associations within the stimulus set, while associations were defined by co-occurrence statistics. The medial frontal gyrus, the posterior cingulate gyrus, the superior temporal gyrus and the right hippocampus revealed U-shaped activation functions with greater activations for high-confidence OLD and NEW decisions. This was independent of the associative memory manipulation, which suggests that not episodic memory, but rather processes related to confidence account for the activation in these brain regions. In contrast, left hippocampus followed a different activation pattern that was modulated by the amount of associations. This provides evidence for the role of the left hippocampus in associative memory.