Castro-Rodrigues, PedroAkam, ThomasSnorasson, IvarCamacho, MartaPaixão, VitorMaia, AnaBarahona-Corrêa, J. BernardoDayan, PeterSimpson, H. BlairCosta, Rui M.Oliveira-Maia, Albino J.2022-07-052022-07-052022-05Castro-Rodrigues, P., Akam, T., Snorasson, I., Camacho, M., Paixão, V., Maia, A., Barahona-Corrêa, J. B., Dayan, P., Simpson, H. B., Costa, R. M., & Oliveira-Maia, A. J. (2022). Explicit knowledge of task structure is a primary determinant of human model-based action. Nature human behaviour, 10.1038/s41562-022-01346-2. Advance online publication. https://doi.org/10.1038/s41562-022-01346-2http://hdl.handle.net/10400.26/41275Explicit information obtained through instruction profoundly shapes human choice behaviour. However, this has been studied in computationally simple tasks, and it is unknown how model-based and model-free systems, respectively generating goal-directed and habitual actions, are affected by the absence or presence of instructions. We assessed behaviour in a variant of a computationally more complex decision-making task, before and after providing information about task structure, both in healthy volunteers and in individuals suffering from obsessive-compulsive or other disorders. Initial behaviour was model-free, with rewards directly reinforcing preceding actions. Model-based control, employing predictions of states resulting from each action, emerged with experience in a minority of participants, and less in those with obsessive-compulsive disorder. Providing task structure information strongly increased model-based control, similarly across all groups. Thus, in humans, explicit task structural knowledge is a primary determinant of model-based reinforcement learning and is most readily acquired from instruction rather than experience.engjournal article10.1038/s41562-022-01346-2