Figure 1.

Memory task overview and performance. (A) Memory task schematic. In the delayed free-recall task, subjects encoded a list of 12 items (words) presented sequentially, followed by an arithmetic distractor and verbal free recall, for up to 26 lists in a session. In a given session, all study lists contained either unrelated items or items belonging to one of three semantic categories. (B) Localized intracranial electrodes overlaid on an average brain surface. Electrodes are coloured by patient group (orange: TBI group, blue: non-TBI group). (C) Recall performance. Serial position curves plot the average probability of recall at each list position for the two groups. The TBI group trended towards lower recall performance compared to the non-TBI group [χ²(1) = 3.2, P = 0.07]. The TBI group has significantly decreased recall performance in the categorized task {group × task interaction: [χ²(1) = 5.87, P = 0.015]}. (D) Temporal clustering in recall. For each subject, we plot temporal clustering scores, with the group mean and standard error. The dotted line at 0.5 represents random chance. Both groups show temporal organization of their recall sequence, with no statistical difference between groups [t(217) = −0.84, P = 0.40]. (E) Semantic clustering in recall. For each subject performing the categorized task, we plot the adjusted ratio of clustering score with group mean and standard error. Maximum clustering at 1 and no clustering at 0. Both groups exhibit semantic clustering of their recall sequences, with no significant difference between groups [t(103) = 0.04, P = 0.96]