In both panels, markers in red, blue and green represent electrodes from participants P1, P2 and P3, respectively. For each participant, the electrode with the highest d′-value is marked with a shaded halo. The red square marker in each plot represents the control electrode also shown in . (a) Selectivity index values increase in parallel with d′-values (n=14, Spearman’s rank correlation, r=0.8, P=0.0007). (b) Co-occurrence values for the HFB increase in the experimental condition are also correlated with the selectivity index values. Electrodes with higher selectivity index during experimental condition showed higher co-occurrence of HFB peaks during experimental arithmetic condition (n=14, Pearson’s correlation, r=0.9, P=1e−5).