Figure 4. Ripple activity pattern similarity reflects memory semantization.
(A) Distance (dissimilarity) between the average pattern during semantic trials and the average patterns emerging during the 4 memory age categories of autobiographical trials (i.e., statements referring to “today,” “yesterday,” “this week,” and “last month”). Note the growing resemblance between autobiographical and semantic patterns as memories become more remote. Error bars represent bootstrap SE.
(B) The distances (dissimilarity) between ripple rate patterns associated with individual memory items and the average semantic pattern showed a significant negative correlation with memory age (Spearman’s ρ = −0.47, p < 10−7, n = 115 memory items; dashed line is the least-squares line). Thus, the more remote the autobiographical memory was, the more similar its associated ripple rate pattern was to semantic memory.
(C) Agglomerative hierarchical clustering (using group-average linkage) applied to the average ripple rate patterns of the different conditions reveals that multisite ripple activity forms a hierarchy of pattern similarity that reflects the episodic-semantic continuum.
See also Figure S4.