Fig. 3: Ripples in the human hippocampus are linked to behavioral state and memory performance in an associative object–location memory task.
From: Ripple-locked coactivity of stimulus-specific neurons and human associative memory
a, Ripple characteristics during the different trial phases (n = 62 channels). As compared to ITI periods, ripple rates were increased during cue periods and reduced during retrieval, feedback and re-encoding periods (repeated-measures ANOVA: P < 0.001). Ripple durations showed a similar pattern as ripple rates (P = 0.046) but no significant post hoc comparisons. Ripple frequency was not modulated by trial phase (P = 0.690). b, Correlations between ripple rates and memory performance (n = 62 channels). For each channel, we computed across-trial correlations between ripple rates in a given trial phase and memory performance during the retrieval phase, and we tested the correlation values against 0 across channels (two-sided t-tests with Bonferroni correction for multiple comparisons). Increased ripple rates during cue periods were associated with better memory performance in the subsequent retrieval periods (Pcorr. = 0.038), and retrieval periods with poorer performance were followed by increased ripple rates during subsequent re-encoding periods (Pcorr. < 0.001). c, Time-resolved ripple occurrence across all trials as a function of absolute time relative to the onset (cue and feedback) or offset (ITI, retrieval and re-encoding) of a given trial phase (dashed vertical lines). Each dot is a ripple (colored dots, ripples during good-performance trials; gray dots, ripples during bad-performance trials). Colored lines and shadings, ripple rates during good-performance trials (‘good trials’; mean ± s.e.m. across channels); gray lines and shadings, ripple rates during bad-performance trials (‘bad trials’; mean ± s.e.m. across channels). Black shadings at top indicate time periods with significant differences between good and bad trials (two-sided cluster-based permutation tests: P < 0.025). d, Correlations between ripple rates and trial index (n = 62 channels). We tested the correlation values against 0 afterward (two-sided t-tests with Bonferroni correction). Ripple rates during feedback decreased over time (Pcorr. = 0.012). Box plots in a, b and d show center line, median; box limits, upper and lower quartiles; whiskers, minimum and maximum; and points, outliers. *Pcorr. < 0.05 and ***Pcorr. < 0.001.
