Investigating the functional specialization of human declarative memory subsystems

Introduction. While traditional models of systems memory consolidation postulate the reliance of freshly encoded memories on the hippocampus, recent evidence in humans and animals has shown that there are conditions under which the neocortex can rapidly acquire genuine memory engrams. The current study investigates the idea of concurrent memory encoding in the entire network, and specialized subsystems coding for different aspects of the memory. Methods. 80 participants encoded the same abstract visual stimuli during fMRI scanning and were instructed to either remember the detailed item-context combinations (DET) or to identify conceptual categories (CEP). 24h later performance was tested in a categorization and an itemcontext recognition task. Results. CEP performed better in categorizing novel stimuli (t(78)=-6.91; p<0.001), whereas DET had better memory for item-context combinations (t(78)=6.31; p<0.001). In both groups, repetitions activated the precuneus, for exact items (p<0.05) as well as conceptual repetitions (p<0.05). Contrasting the two groups, exact item repetition elicited higher bilateral activation of the superior frontal gyrus (t=7.03; p<0.05), caudate and thalamus in DET (t=5.88; p<0.05), and higher activation in visual cortex extending towards precuneus and fusiform gyrus (t=7.51; p<0.05) in CEP. Comparing CEP with DET, activation in medial occipital cortex (t=6.83, p