ELSC Seminar Series

Standard systems consolidation theories posit that all declarative memories initially depend on the hippocampus but over time these same memories come to be represented by the neocortex independently of the hippocampus. These theories are no longer widely accepted in light of overwhelming evidence that detail-rich event memories always require hippocampal representations, while neocortical regions represent more generalized or schematized memories. More modern views of systems consolidation concede that detailed memories are always hippocampal-dependent but maintain that neocortical memories, even generalized schematic ones, can only be built over time through hippocampal support.
In this talk I will suggest that the notion of systems consolidation may itself be a misnomer. A more useful way to think about memory as multiple interactive systems that are always in flux. By this view there are multiple forms of representations that co-exist but are differentially expressed (e.g. event-specific detailed memory, event-specific gist memory, event-general schemas and abstract semantic memories). Different forms of representations can all be created or modulated at the time of an event. Which memory is expressed at any given time depends on factors such as relevance to current goals, attention, context specificity or relatedness to prior knowledge. Memories are altered through interactive (bi-directional), dynamic changes in strength, composition and dominance of expression, influenced by task demands and time. Thus, neocortical representations can be modified by hippocampal input, and under certain conditions may even depend on it before stabilization, but the reverse is also true. Hippocampal memory trace formation is shaped by cortical representations of prior knowledge. These forms of representation continue to interact with one another, modify each other and compete for expression throughout the life of a memory. There is no unidirectional time-dependent biological process of memory trace transformation or migration; there is only synaptic consolidation and re-consolidation that is modulated by interactions with various other neural representations. Because hippocampal memory representations are so dominant early on, and because the tasks used over the years have tended to tap detailed event-specific memories, neuroscience research has rarely measured expressions of cortical representations at short delays, and has mistaken differences in the dynamics of memory expression for a process of systems consolidation.