Figure 3. Group-averaged activations. (A) Episodic retrieval task and (B) High-load working memory task ( p < .001 uncorrected, 10 voxel cluster threshold).
significant activations in the bilateral middle frontal gy- rus (BA 9/46), bilateral inferior frontal gyrus (BA 44/45), anterior cingulate gyrus (BA 32), and bilateral parietal cortex (BA 7) (for a complete summary of significant activations, see Table 4). For the low-load condition, we again observed significant group activations in bilat- eral middle frontal gyrus (BA 9/46), bilateral inferior frontal gyrus (BA 44/45), anterior cingulate gyrus (BA2 4/32), and bilateral parietal cortex (BA 7/40) (for com- plete summary of activations, see Table 5).
Global WMH and PFC activity. As shown in Figure 4, for the high-load condition, global WMH volume was negatively correlated with left (R = .654, p = .007) and right (R = .607, p = .015) dorsal PFC activity. In addition, global WMH volume was negatively correlated with ventral PFC activity, but these effects were not statistically significant (right: R = .438, p = .104; left: R = .479, p = .071). For the low-load condition, the pattern of results is similar to the results for the high-
Journal of Cognitive Neuroscience
load condition, albeit with less robust correlations (dorsal PFC: left R = .447, p = .096; right R = .491 p = .063; ventral PFC: left R = .362, p = .189, right R = .501, p = .057).
Dorsal PFC WMH and brain activity. As shown in Table 3, dorsal PFC WMH volume was significantly negatively correlated with bilateral dorsal and ventral PFC activations. Outside of the PFC, we delineated additional ROIs based on the group-averaged activations in areas that have been consistently identified in imaging studies of verbal working memory. Specifically, we were interested in the anterior cingulate cortex (BA 24/32) and posterior parietal cortex (BA 7/40), two areas that are commonly activated during working memory tasks (see Smith & Jonides, 1999). Also shown in Table 3, dorsal PFC WMH volume was also significantly negatively correlated with the anterior cingulate and left parietal cortex. A similar correlation was observed in the right parietal cortex, but was not statistically significant. For
Volume 18, Number 3