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Abstract

In a dynamically changing environment, we are constantly required to flexibly react to stimuli. It is therefore necessary to adapt behaviour to environmental cues, as well as to successfully perceive relevant stimuli. The present work addressed the question of which brain areas form the basis for task preparation and decisions along the processing chain from stimuli to responses. It combined functional magnetic resonance imaging with multivariate pattern classification to search for the encoding of specific contents of mental processes. The first study demonstrated, using a task switching paradigm, that task-sets were first encoded in left intraparietal sulcus, preceding left posterior ventrolateral prefrontal cortex. This finding emphasises the importance of parietal cortex in establishing abstract rules in a cued task context. In the second study, the visibility of response-relevant target objects was varied. It was found that the lateral-occipital complex (LOC) only encoded perceptual decisions about highly visible objects. The precuneus, on the other hand, encoded random guessing decisions made with insufficient visual input. Contradicting classical signal detection models, this finding emphasises the notion of two modes for perceptual decision making depending on stimulus visibility. The third study demonstrated a shared neural substrate for random guessing and free decisions in the precuneus, suggesting a general role for the generation of internal decisions. Additionally, anterior medial prefrontal cortex was exclusively engaged when decisions were intended to be made without an external frame of reference. In summary, the present work highlights the importance of parietal cortex in controlling both rule-guided and self-determined behavior in humans. Parietal cortex functions might be best described as related to multi-modal information integration and processing of highly self-referenced intentions.