Human prefrontal cortex independently encodes future task-sequences and their order

Every day we need to plan and coordinate multiple future tasks. Previous studies have shown that rostral prefrontal cortex encodes individual future tasks across delays. However, so far it remains unclear how the brain encodes an ordered sequence of upcoming tasks across delays. Here, participants were scanned as they remembered to execute a single future task (single-task trials) or sequences of two tasks (sequence trials). A multivariate classifier was trained on patterns of BOLD activity that encode the single tasks, and was used to decode the identity of the same tasks when they were either first or second in a remembered sequence. The sequential order of tasks (e.g. AB vs. BA) was separately decoded. We found the following. (1) Both the first and the second upcoming tasks could be decoded from rostrolateral prefrontal and parietal cortices. (2) Sequence order was encoded in dorsomedial and dorsolateral PFC. (3) ROI analysis revealed that regions encoding the future tasks and regions encoding sequence order did not overlap. Our findings suggest that (a) the brain encodes future task sequences in a compositional fashion, and (b) there may be a segregation of task and order information in the PFC. Namely, while rostrolateral PFC encoded the identity of multiple future tasks, dorsomedial and dorsolateral PFC encoded information required for the orderly execution of abstract tasks.