Hemispheric Specialization During Episodic Memory Encoding in the Human Hippocampus and MTL

摘要: Hemispheric Specialization During Episodic Memory Encoding in the Human Hippocampus and MTL Daniel J. Casasanto† (dcasasan@mail.med.upenn.edu) William D. S. Killgore† (killgore@mclean.harvard.edu) Guila Glosser† (glosser@mail.med.upenn.edu) Joseph A. Maldjian‡ (maldjian@oasis.rad.upenn.edu) John Detre†‡ (detre@mail.med.upenn.edu) Departments of Neurology Radiology, University Pennsylvania Medical Center 3400 Spruce Street, Philadelphia, PA 19104 USA Abstract specialization during episodic memory encoding was examined using three functional magnetic resonance imaging (fMRI) tasks. Stimuli for tasks differed degree to which they elicited subjects’ use verbal image- based strategies. Intentional visually presented scenes, sentences, faces associated with neural activity hippocampus surrounding mesial Temporal Lobe (mTL) structures. Across tasks, material- specific lateralization observed posterior mTL. In contrast, hippocampal activation did not lateralize according material type two These results suggest a dissociation between other mTL subcomponents, indicate that material-specificity may fully explain hemispheric system. Introduction The human adjacent temporal lobe structures are believed subserve new information into memory: form long-term supports conscious recollection ongoing experiences (Squire Zola-Morgan, 1991; Tulving, 1998). role processing has been investigated extensively ever since Scoville Milner (1957) reported profound global anterograde amnesia patient HM following bilateral resection hippocampus, uncus, amygdala. Numerous studies unilateral have documented left-language dominant patients, left anterior consistently produces impairment, although findings less robust, right, non- language-dominant visuospatial impairment (Milner, 1958; Blakemore Falconer, 1967; Milner, 1968; Jones- Gotman, 1986). Such gave rise ipislateral deficit model, or material-specific asserts function lateralizes cerebral function: individuals, hemisphere mediates memory, right (Saykin, et al., 1992). Neuroimaging entirely consistent lesion data regarding processing. Although several demonstrated laterality frontal lobes (Wagner, 1998; McDermott, 1999) (Grady, 1995; Stern, 1996; Nyberg, 1996a; Kelly, Detre, 1998), numerous effects depend upon process being instantiated (encoding vs. retrieval), rather than stimulus (Tulving, 1994; Schacter, 1996b). Other medial regions respond differentially novel familiar stimuli Fujii, 1997), varies depth (Nyberg, Martin, success (Casasanto, 2000), task parameters such as presentation rate (Kelly, present study fMRI intentional unfamiliar faces, complex visual four-word declarative sentences. goal determine whether presented. variables affect laterality, novelty, instructions, parameters, were held constant across It hypothesized would be preferential right-hemisphere structures, sentences left- amenable both encoding, activation. Materials Methods Subjects Healthy, normal volunteers ages 18 30 consecutively recruited from community, paid $20 their