Functional interactions between the medial temporal lobes and posterior neocortex related to episodic memory retrieval

We applied structural equation modeling to positron emission tomographydata in humans to examine functional interactions between the right medialtemporal lobe (MTL) and selected right neocortical regions in relation tovisual recognition memory. Using a priori knowledge about anatomicalconnections between these regions as a guiding constraint, we modeled thepattern of interactions [i.e. covariances in regional cerebral blood flow(rCBF)] associated with episodic memory retrieval of spatial location andcompared it with the pattern for retrieval of object identity. We alsocompared these patterns with those associated with perceptual matching ofspatial location and object identity. Although displaying no difference inaverage rCBF across tasks, the right MTL showed domain-specific qualitativedifferences in interactions with posterior dorsal (parieto-occipitalsulcus, supramarginal gyrus) and ventral regions (fusiform gyrus, superiortemporal sulcus) but not with a prefrontal region. MTL interactionsinvolving dorsal regions were positive in the spatial retrieval task butnegative for object retrieval. Interactions involving ventral regionsshowed the reverse pattern. No comparable changes were observed duringperceptual matching. Using control models, we demonstrated theneuroanatomical specificity of these results. Our results provide supportfor the notion that the nature of interactions between the MTL andposterior neocortex depends on the domain of information to-be- recovered.