Domain- and Process-specificity in the Medial Temporal Lobes

The present thesis addresses the role of structures in the human medial temporal lobe (MTL) in memory formation and retrieval. More specifically, guided by a detailed consideration of the anatomical connections both amongst the subregions of the MTL and between the MTL and regions of the neocortex, two principles of the functional organization of the MTL are explored: domain-specificity and process-specificity. Domain-specificity refers to the idea that the neurocognitive processes underlying memory performance may differ depending on the sensory domain of the processed stimuli. This is of particular relevance because recent anatomical investigations suggest that subregions of the primate MTL have distinct patterns of connections with sensory cortices. Process-specificity, on the other hand, refers to the idea that psychologically different processes may support memory performance on a recognition task. That is, successful recognition may be supported by a mere sense that an item has been studied previously (familiarity) or by the successful retrieval of spatio-temporal context or associative information (recollection). In the first two Studies of this thesis, the neural systems underlying memory for auditory and visual context information were explored in the light of the hypothesis of domain-specificity in the MTL. Study 3 investigated process-specific impairments in verbal recognition memory following unilateral MTL pathology. More specifically, this study investigated whether a material-specific lateralization of function (i.e. left-lateralization for verbal stimuli) also holds for verbal recollection. Study 4 investigated the idea that age-related changes in recognition memory, which have often been described to be process-specific, i.e. predominantly affecting recollection, may be additionally affected by word-concreteness. Thus, Study 4 investigated the interaction of stimulus type (concrete vs. abstract words) and process-specific changes in recognition memory during normal aging. Finally, Study 5 of this thesis explored the neural processing underlying associative memory formation using a novel associative encoding paradigm. Regions of the MTL 3 (parahippocampal cortex and hippocampus) along with medial prefrontal and retrosplenial cortices have been suggested to support the representation of contextual associations. We investigated whether these structures are also activated when subjective associations are evoked during memory encoding, and how spontaneously evoked associations during encoding affect subsequent recognition memory performance.