Figure 3. Multisite patterns of ripples discriminate between autobiographical and semantic memory.

(A) Averaging over electrodes within a subject and comparing overall ripple rates across conditions using partially overlapping samples t tests (Derrick et al., 2017) showed no significant difference between autobio and semantic memory (t(14.51) = 0.17, p > 0.87). Similar to the autobio condition, the semantic condition elicited higher ripple rates compared to both math (t(14.17) = 5.27, p < 0.001) and 5-s rest (t(15.06) = 2.98, p < 0.01). Error bars represent SEM.

(B) Schematic depiction of the recording sites’ functional specialization in MNI space, showing a mixed and balanced spatial distribution of memory-type biases. Inset: effect size histogram of the autobiographical versus semantic bias at individual sites, pointing to the absence of clear functional segregation between memory types. Electrodes marked in red or yellow showed a slight bias for autobio or semantic memory, respectively.

(C) Linear discriminant analysis (LDA) classifier trained to decode trial type from multivariate ripple rate patterns (computed across all electrodes pooled together) significantly discriminated between semantic and autobiographical trials. Decoding performance was quantified using F1 score: autobio, 0.70 ± 0.11; semantic, 0.58 ± 0.17; math, 0.88 ± 0.04 (SEM was computed using a jackknife procedure, excluding 1 patient at a time). Filled circles denote the actual results; gray dots show results for same data when trial labels were randomly shuffled; gray crosses indicate the chance level in each class (different due to the different number of items in each class).

(D) Confusion matrix showing that classification errors were primarily due to confusion between autobiographical and semantic trials.

See also Figure S4.