Depth of processing effects on neural correlates of memory encoding - Relationship between findings from across- and within-task comparisons

Neuroimaging studies have implicated the prefrontal cortex and medial tempo ral areas in the successful encoding of verbal material into episodic memor y, The present study used event-related functional MRI to investigate wheth er the brain areas associated with successful episodic encoding of words in a semantic study task are a subset of those demonstrating depth of process ing effects. In addition, we tested whether the brain areas associated with successful episodic encoding differ depending on the nature of the study t ask. At study, 15 volunteers were cued to make either animacy or alphabetic al decisions about words, A recognition memory test including confidence ju dgements followed after a delay of 15 min, Prefrontal and medial temporal r egions showed greater functional MRI activations for semantically encoded w ords relative to alphabetically encoded words, Two of these regions (left a nterior hippocampus and left ventral inferior frontal gyrus) showed greater activation for semantically encoded words that were subsequently recognize d confidently, However, other regions (left posterior hippocampus and right inferior frontal cortex) demonstrated subsequent memory effects, but not e ffects of depth of processing. Successful memory for alphabetically encoded words was also associated with greater activation in the left anterior hip pocampus and left ventral inferior frontal gyrus, The findings suggest that episodic encoding for words in a semantic study task involves a subset of the regions activated by deep relative to shallow processing. The data prov ide little evidence that successful episodic encoding during a shallow stud y task depends upon regions different from those that support the encoding of deeply studied words. Instead, the findings suggest that successful epis odic encoding during a shallow study task relies on a subset of the regions engaged during successful encoding in a deep task.