Extended Data Fig. 4. Category neuron selection and persistent activity.

(a) In hippocampus, amygdala, and vmPFC (all p = 0.002, right-sided permutation test) the selected number of category neurons was larger than expected by chance (p < 0.01; Bonferroni corrected; see Methods). The null distribution (grey) was estimated by repeating the selection procedure after shuffling the category labels for 500 times. Numbers of selected neurons in dACC and pre-SMA were not significantly different from those expected by chance. (b). Category neurons in both areas of the MTL, hippocampus (n = 89; pref. vs. baseline: p = 0.0001; non-pref.: p = 0.0001) and amygdala (n = 181; pref.: p = 0.0001; non-pref.: p = 0.0001), showed persistent activity during the delay period of the task, during which no picture was presented on the screen. Note that category neurons were selected during the encoding period only, making the delay period independent from the selection criteria. FR remained significantly higher when their preferred as compared to non-preferred categories were maintained in memory (hippocampus: p = 0.025; amygdala: p = 0.037). The activity of category neurons in the vmPFC (right) during the delay period was not significantly larger than that during baseline (n = 37; pref.: p = 0.12; non-pref.: p = 0.26). Also, their FRs did not differ significantly between when the preferred and the non-preferred category of a cell was maintained in WM (t(36) = 1.03, p = 0.32, BF₀₁ = 3.47). The FR of vmPFC neurons thus went back to baseline levels when no stimulus was presented on the screen. FR for selected neurons in the pre-SMA (n = 18) and dACC (n = 14) are shown only for completeness despite the proportion of these cells not exceeding those expected by chance. All comparisons are based on two-sided permutation-based t-tests. Centre values denote mean ± s.e.m. *** p < 0.001, ** p < 0.01, * p < 0.05, ns = not significant.