LONG-TERM MEMORY FOR MOTION DIRECTIONS INDUCES EXPERIENCE-DEPENDENT RESPONSES IN THE VISUAL AREA MST

Traditionally, neocortical declarative memory formation has been viewed as a slow and hippocampus-dependent process. While it has been demonstrated that engrams can form rapidly in higher-order association-cortex, the potential for rapid plasticity of the early visual cortex remains debated. Here, we examine whether memory engrams for basic visual features can develop rapidly in feature-selective visual cortex, with a focus on color and motion direction.
Participants (preliminary n=39, planned 80) learned object-feature associations in five encoding-recall repetitions with concurrent 3T fMRI. During encoding, object-color-motion triplets were presented, and participants encoded either object-color (color group) or object-motion associations (motion group). During recall, objects were presented without feature information to isolate memory-related activity in feature-selective cortex. Memory retention was assessed after 24h.
Behaviorally, participants demonstrated clear evidence of learning and retention over 24h (Fig1A). During memory recall, bilateral activity in motion-sensitive visual area MST increased specifically in the motion group across the recall repetitions (Fig1BC), and these changes remained stable even after 24h. Additionally, repetition-related increases in functional activity within MST were associated with recall performance, highlighting the behavioral relevance of these neural changes (Fig1D).
These findings show rapid, long-lasting and behaviorally relevant plasticity of feature-selective visual cortex in response to learning, which aligns well with emerging evidence for a role of early visual cortex in long-term memory. Furthermore, they indicate that the potential for rapid memory formation might be a fundamental property across the cortical hierarchy. Future diffusion MRI analyses will determine whether functional changes are accompanied by changes in microstructural plasticity.