No abstract

The hippocampus is known to support recollection memory, but the relation between its structure and recollection in healthy adults has not been established. Here we show that the hippocampus (including subiculum, DG, and CA1-CA4), when separated into posterior and anterior segments, can reliably predict recollection in healthy young adults. Better memory was associated with larger posterior and smaller anterior segments, as evaluated relative to the uncal apex. Overall hippocampal volume, however, did not predict memory. This pattern was confirmed in four separate data sets from different studies and laboratories. The relationship between the posterior hippocampus and memory was mediated by the structure's functional connectivity with a neocortical network identified during a postencoding resting-state scan. The relationship was also weakest in an experiment involving no appreciable study-test interval. These findings suggest that enhanced posterior-hippocampal postencoding processes may account for the memory benefit associated with larger posterior hippocampi.

Reports of superior memory for novel relative to familiar material have figured prominently in recent theories of memory. However, such novelty effects are incongruous with long-standing observations that familiar items are remembered better. In 2 experiments, we explored whether this discrepancy was explained by differences in the type of familiarity under consideration or by differences in the difficulty of discriminating targets from lures, which may lead to source confusion for familiar but not novel targets. In Experiment 1, we directly tested whether previously observed novelty effects were the result of novelty, discrimination demands, or both. We used linguistic materials (proverbs) to replicate the novelty effect but found that it occurred only when familiar items were subject to source confusion. In Experiment 2, to examine better how novelty influences episodic memory, we used experimentally familiar, pre-experimentally familiar, and novel proverbs in a paradigm designed to overcome discrimination demand confounds. Memory was better for both types of familiar proverbs. These results indicate that familiarity, not novelty, leads to better episodic memory for studied items, regardless of whether familiarity is experimentally induced or based on prior semantic knowledge. We argue that proposals that state that information is encoded better if it is novel are based on over-generalizations of effects arising from the distinctiveness of novel materials.