Prefrontal gray matter volume mediates age effects on memory strategies.

Age differences in the strategies that individuals spontaneously use to learn new information have been shown to contribute to age differences in episodic memory. We investigated the role of prefrontal structure in observed age effects on self-initiated use of memory strategies. The relationships among age, prefrontal regional gray matter volumes, and semantic and serial clustering during free recall on the California Verbal Learning Test-II were examined across the adult lifespan. Semantic clustering was negatively correlated with age and positively correlated with gray matter volumes in bilateral middle and left inferior frontal regions across the adult lifespan. Gray matter volumes in these regions mediated the effects of age on semantic clustering. Forward serial clustering was also negatively correlated with age. However, forward serial clustering was not significantly positively correlated with gray matter volumes in any region of lateral prefrontal cortex. These results suggest that bilateral middle and left inferior frontal regions support self-initiated semantic memory strategy use across the adult lifespan. They also suggest that age differences in prefrontal gray matter volume are a significant contributor to age differences in self-initiated use of elaborative memory strategies.