Functional Magnetic Resonance Imaging of Semantic Memory Processes in the Frontal Lobes

Abstract

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Assembling and encoding word representations: fMRI subsequent memory effects implicate a role for phonological control

“…As noted above, an unexpected aLIPC response was observed during performance of the phonological processing task, with the magnitude of activation being greater during pseudo-English relative to English word processing. Prior studies indicate that aLIPC may be differentially engaged during semantic relative to phonological analysis [25,32,34], with some theorists positing a role for this region in controlled access to long-term semantic representations [6,9,19,21,30,36,46]. The presently observed response, albeit in a more anterior (bordering on frontopolar) region to that often observed in semantic retrieval studies, raises the possibility that aLIPC contributions may not be restricted to controlled semantic retrieval.…”

“…The focus of this response fell just anterior to the aLIPC region frequently implicated in controlled semantic retrieval [6,9,19,21,30,36,46], whereby task-relevant semantic knowledge is recovered from long-term memory in the course of goal-directed behavior. In particular, this focus was anterior to previous foci associated with controlled semantic retrieval (MNI: −51, 21, −12; [53] Recent data have raised questions regarding the nature of the selectivity of aLIPC computations.…”

“…This analysis further probed whether the magnitude of the subsequent memory effect differed for novel and familiar words, and, if so, whether there was evidence for such differences to be greater in parietal regions associated with on-line phonological storage or frontal regions associated with phonological assembly and rehearsal. Finally, the differential response of anterior left inferior prefrontal cortex (aLIPC; ∼BA 47/45) across word types was indexed as the present design permits an assessment of whether this region, which has been previously associated with controlled semantic retrieval [6,9,19,21,30,36,46], is also engaged during phonological processing conditions.…”

Neural mechanisms of visual object priming: evidence for perceptual and semantic distinctions in fusiform cortex

“…Reduced neural activity for repeated stimuli was observed in fusiform and lateral occipital regions that have been associated principally with visual perceptual Henson et al, 2000;Wiggs and Martin, 1998) and lexical/semantic Martin and Chao, 2001;Mummery et al, 1999;Simons et al, 2001;Thompson-Schill et al, 1999) processing, as well as in inferior prefrontal regions that are thought to be involved in the controlled selection and/or retrieval of lexical and semantic information (Dapretto and Bookheimer, 1999;Fletcher and Henson, 2001;Gabrieli et al, 1996;Martin and Chao, 2001;Poldrack et al, 1999;ThompsonSchill et al, 1997;Wagner et al, 2001). …”

“…During visual object priming, for example, some of the regions exhibiting significant activation associated with initial visual processing of objects show reduced activation during repeated processing of the objects Henson et al, 2000;Wagner et al, 1997;Wiggs and Martin, 1998). These regions include fusiform and lateral occipital cortices associated with visual perception and lexical/semantic processing Grill-Spector et al, 1999;Henson et al, 2000;Martin and Chao, 2001;Simons et al, 2001;Thompson-Schill et al, 1999), as well as inferior prefrontal cortices thought to play a role in the controlled retrieval of lexical/semantic information (Dapretto and Bookheimer, 1999;Fiez, 1997;Gabrieli et al, 1996;Martin and Chao, 2001;Poldrack et al, 1999;Wagner et al, 2000Wagner et al, , 2001.…”