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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.
