Extended Data Fig. 5: Additional analyses for category cells in the MTL.

(a) Unlike for preferred trials, we did not observe a load effect for MTL category cells when non-preferred categories were maintained during the maintenance period (n = 270). (b) In addition to our statistics across single neurons, we performed nested random-intercept GLMs for patient-level statistics⁸⁴. In the hippocampus, FR of category cells was significantly higher for preferred as compared to non-preferred as well as for correct vs. incorrect trials. There was no main effect of load as expected, which only emerged when we tested for load differences in preferred trials only (data not shown). In the amygdala, we observed a significant effect for preference, where FR was higher in preferred than non-preferred trials. Again, the load effect was only significant when tested in preferred trials only (data not shown). There was no effect for accuracy. (c) When averaging theta band (3–7 Hz) SFC values for hippocampal category neurons paired with significant PAC channels, we did not observe a significant main effect for load or preference nor a significant interaction (n = 151; permutation-based F-test). (d) We performed a median split of gamma amplitudes across trials and tested gamma SFC between category cells and significant PAC channels in the hippocampus separately for spikes that occurred during high and low gamma amplitudes (spike counts were adjusted across conditions). We observed a significant difference in gamma SFC between preferred and non-preferred trials only for spikes that occurred during high (n = 151, p = 0.0015), not during low gamma amplitudes (n = 151, p = 0.84). (e) When paired with non-PAC channels, we did not observe differences in the gamma band between preferred and non-preferred trials for normalized SFC values for category cells in hippocampus or amygdala. In the hippocampus, we observed a significant difference in the alpha range (7–11 Hz) with SFC for non-preferred trials higher than for preferred trials, which we did not further consider in our analyses. (f) Comparing SFC for category neurons across all channels (not separated into PAC/Non-PAC channels) revealed significantly higher gamma-band SFC for preferred than non-preferred trials in the hippocampus (cluster-p = 0.007, two-sided cluster-based permutation t-test with Bonferroni-corrected alpha-level for two MTL areas), similar to what we observed for PAC channels only. There were no significant differences in the amygdala. (g) To test whether the gamma SFC effect for category cells in the hippocampus persisted at the patient level, we averaged gamma SFC across all category neuron to channel pairs within each patient and then compared the per-patient average between preferred and non-preferred trials. Patient-averaged gamma SFC was significantly higher for preferred trials, suggesting that the effect was not driven by a few channels or patients (n = 19, t(18) = 2.8512, p = 0.005). In (a,c,d,g), we performed two-sided permutation-based t-tests. Centre values demote mean ± s.e.m (coloured areas in e,f). *** p < 0.001; ** p < 0.01; * p < 0.05; ns = not significant.