CORTICAL NETWORKS IMPLICATED IN SEMANTIC AND EPISODIC MEMORY - COMMONOR UNIQUE

While previous functional neuroimaging studies have shown that semanti c and episodic memory tasks activate different cortical regions, they never compared regional cerebral blood flow (rCBF) patterns associated with semantic and episodic memory within the same experimental design . In this study, we used (H2O)-O-15 PET to study subjects in the cours e of semantic and episodic memory tasks, rCBF was measured in 9 normal volunteers during a resting baseline condition and two cognitive task s. In the semantic categorisation task subjects heard a list of concre te words and had to respond to words belonging to the ''animals'' or ' 'food'' category. In the episodic recognition task subjects heard a li st of concrete words, half ''old'', i.e. belonging to the list of the semantic categorisation task, and half ''new'', i.e. presented for the first time. Subjects had to respond to the ''old'' words. Both tasks were compared to a resting condition. Statistical analysis was perform ed with Statistical Parametric Mapping (SPM). Compared to the resting condition, the semantic tasks, activated the superior temporal gyri bi laterally, the left frontal cortex, and right premotor cortex. The epi sodic tasks activated the left superior temporal gyrus, the frontal co rtex bilaterally, and the right inferior parietal cortex. Compared to the episodic memory tasks, the semantic memory tasks activated the sup erior temporal/insular cortex bilaterally and the right premotor corte x. Compared to the semantic memory tasks, the episodic memory tasks ac tivated the right frontal cortex. These results suggest that cortical networks implicated in semantic and episodic memory show both common a nd unique regions, with the right prefrontal cortex being the neural c orrelate specific of episodic remembering.