Item

Abstract

Aims. 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
item-context recognition task. Results. CEP performed better in categorizing novel stimuli (t78=-6.91; p<0.001), whereas DET
had better memory for item-context combinations (t78=6.31; p<0.001). In both groups, repetitions activated the precuneus, for
exact items (pFWE<0.05) as well as conceptual repetitions (pFWE<0.05). Contrasting the two groups, exact item repetition
elicited higher bilateral activation of the superior frontal gyrus (t=7.03; pFWE<0.05), caudate and thalamus in DET
(t=5.88; pFWE<0.05), and higher activation in visual cortex extending towards precuneus and fusiform gyrus
(t=7.51; pFWE<0.05) in CEP. Comparing CEP with DET, activation in medial occipital cortex (t=6.83, pFWE<0.05) increased
over category repetitions only in CEP. Discussion. Our data suggest the precuneus as a hub for detailed as well as
conceptual memory representations. Additionally, differences in memory performance and neural differences between the
two groups indicate a functional specialization of neocortical and subcortical areas during prioritized encoding of similar vs.
differential features.