Structured memory representations develop at multiple time scales in hippocampal-cortical networks.

Area of Science:

• Neuroscience
• Cognitive Science
• Psychology

Background:

• Systems memory consolidation theories propose distinct roles for the hippocampus (rapid event representations) and neocortex (slow schema extraction).
• The temporal dynamics of memory consolidation across brain regions and extended timescales lack empirical validation.

Approach:

• Longitudinal functional magnetic resonance imaging (fMRI) was used to track brain activity in human participants over three months.
• Participants learned structured information through repeated exposure to fractal sequences.

Key Points:

• Sequence-specific representations emerged first in the hippocampus (1-2 weeks), followed by visual and prefrontal cortices.
• Schematic, sequence-general representations appeared in the prefrontal cortex (3 weeks), then medial temporal and anterior temporal lobes.
• Both hippocampal and neocortical representations demonstrated sustained, rather than time-limited, dynamics.

Conclusions:

• Hippocampal and neocortical memory representations emerge at different timescales, reflecting a gradient of abstraction.
• Memory representations persist and coexist across multiple brain regions and levels of abstraction throughout learning.