Abstract
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.
Highlights
Recent neuroimaging studies have drawn increasing attention to the idea that frontal cortical areas may contribute to human memory; the nature of the contributions of these areas is incompletely understood
An examination of the patterns of activations reported across the literature suggests that there may be both code- and set-speciac effects in the frontal cortex; further, these effects appear to occur in distinct frontal regions
The primary goal of the present experiment was to determine whether both code-speciac and setspeciac activation patterns would be manifested in distinct regions of the frontal cortex, within a single group of subjects
Summary
Recent neuroimaging studies have drawn increasing attention to the idea that frontal cortical areas may contribute to human memory; the nature of the contributions of these areas is incompletely understood (see Buckner, 1996; Cabeza & Nyberg, 1997; Desgranges, Baron, & Eustache, 1998; Fletcher, Frith, & Rugg, 1997, for reviews). A right-lateralized region of the frontal polar cortex (at or near BA 10) has been shown to be active across a variety of episodic retrieval tasks (Andreasen et al, 1995; Buckner, Koutstaal, Schacter, Wagner, & Rosen, 1998b; Buckner et al, 1995, 1996, 1998a; Fletcher et al, 1995; Haxby et al, 1996; Rugg, Fletcher, Frith, Frackowiak, & Dolan, 1996; Schacter, Alpert, Savage, Rauch, & Albert, 1996; Schacter, Buckner, Koutstaal, Dale, & Rosen, 1997; Squire et al, 1992; Tulving, Kapur, Craik, Markowitsch, & Houle, 1994; for reviews see Buckner, 1996; Cabeza & Nyberg, 1997) This region has been argued by some to represent the “set” or goal of trying to retrieve past experiences (Buckner et al, 1998a; McDermott et al, in press; Nyberg, Cabeza, & Tulving, 1996; Tulving et al, 1994; Wagner, Desmond, et al, 1998), the exact function of the region is still controversial (MacLeod, Buckner, Miezin, Petersen, & Raichle, 1998; Nolde, Johnson, & Raye, 1998; Rugg et al, 1996; Schacter et al, 1996). The conjoint result of code-speciac effects (as discussed above, for one region of the frontal cortex) along with set-speciac effects (in a separate region of the frontal cortex) would provide a powerful functional dissociation and may help resolve the complex relation between frontal regions and processing operations engaged during human memory task performance.
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