The fate of the memory trace across time: Changes of representations of memories in networks – A new theoretical framework of systems memory consolidation

ⓘ Image creditCourtesy of Richard Kempter

We propose a mechanistic framework for systems memory consolidation of declarative memories that explains why and how memory systems reorganize, that motivates in which way memories change, and that suggests where memories are represented at which time after their acquisition. We therefore propose a new theory that does not rely on previous widespread assumptions in traditional models that declarative memories are initially stored only in the hippocampus and then transferred to neocortical networks. A key element of our new theory is a mechanism that explains the interaction of memory networks that leads to the change of the representations of memory items, which serves the goals to prolong memory lifetime and facilitate new learning.

Archive – B01 (SFB1315/1)

Archive – B01 (SFB1315/2)

ⓘ Image creditImage courtesy of B01

Graphical abstract: Schematic of transformations of memory representations (from left to right). The neocortex (first panel, top) has developed over years representations of concepts (selectivity of neurons color coded) of the sensory world; neurons may also exhibit mixed selectivity (e.g. half red/half blue disc); hippocampal neurons (bottom) are not selective at this early developmental stage. Important/salient concepts presented separately (second panel, colored arrows at top separated by “or”) evoke activity in concept cells in the hippocampus (bottom) via strengthened connections (black lines) (WP1). Formation of symmetric backprojections (second panel, same black lines; WP2) is required for consolidation. One-shot encoding of an association between two simultaneously presented concepts (third panel, colored arrows at top connected by “and”) strengthens connections predominantly in the hippocampus (third panel, solid lines) but also in the neocortex (dotted lines) (WP3). The association encoded in the hippocampus is transferred to the neocortex (fourth panel, solid black lines) as a result of systems memory consolidation (WP2, WP3). Repeated consolidation of associations and control of mean neocortical activity/connectivity (fifth panel, thicker black lines and changed colors of neurons) transforms the neocortical representations (WP4).