  We apply Dynamic Causal Models to electrocorticogram recordings from two
macaque monkeys performing a problem-solving task that engages working memory,
and induces time-on-task effects. We thus provide a computational account of
changes in effective connectivity within two regions of the fronto-parietal
network, the dorsolateral prefrontal cortex and the pre-supplementary motor
area. We find that forward connections between the two regions increased in
strength when task demands increased, and as the experimental session
progressed. Similarities in the effects of task demands and time on task allow
us to interpret changes in frontal connectivity in terms of increased
attentional effort allocation that compensates cognitive fatigue.
