Set- and code-specific activation in frontal cortex: an fMRI study of encoding and retrieval of faces and words

The frontal cortex has been described as playing both "set-specific" and "code-specific" roles in human memory processing. Set specificity refers to the finding of goal-oriented differences in activation patterns (e.g., encoding relative to retrieval). Code specificity refers to the finding of different patterns of activation for different types of stimuli (e.g., verbal/nonverbal). Using a two (code: verbal, nonverbal) by two (set: encoding, retrieval) within-subjects design and fMRI, we explored the influence of type of code and mental set in two regions in the frontal cortex that have been previously shown to be involved in memory. A region in the dorsal extent of the inferior frontal gyrus (BA 6/44) demonstrated code-specific effects. Specifically, an interaction of material type with hemisphere was obtained, such that words produced predominantly left-lateralized activation, whereas unfamiliar faces elicited predominantly right-lateralized activation. A region of the right frontal polar cortex (in or near BA 10), which has been activated in many memory retrieval studies, showed set-specific activation in that it was more active during retrieval than encoding. These data demonstrate that distinct regions in the frontal cortex contribute in systematic yet different ways to human memory processing.