When performing tasks, humans are thought to adopt task sets that configure moment-to-moment data processing. Recently developed mixed blocked/event-related designs allow task set-related signals to be extracted in fMRI experiments, including activity related to cues that signal the beginning of a task block, "set-maintenance" activity sustained for the duration of a task block, and event-related signals for different trial types. Data were conjointly analyzed from mixed design experiments using ten different tasks and 183 subjects. Dorsal anterior cingulate cortex/medial superior frontal cortex (dACC/msFC) and bilateral anterior insula/frontal operculum (aI/fO) showed reliable start-cue and sustained activations across all or nearly all tasks. These regions also carried the most reliable error-related signals in a subset of tasks, suggesting that the regions form a "core" task-set system. Prefrontal regions commonly related to task control carried task-set signals in a smaller subset of tasks and lacked convergence across signal types.

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Participants viewed objects in the central visual field and then named either same or different depthorientation views of these objects presented briefly in the left or the right visual field. The differentorientation views contained either the same or a different set of parts and relations. Viewpoint-dependent priming was observed when test views were presented directly to the right hemisphere CRH), but not when test views were presented directly to the left hemisphere CUI). Moreover, this pattern of results did not depend on whether the same or a different set of parts and relations could be recovered from the different-orientation views. Results support the theory that a specific subsystem operates more effectively than an abstract subsystem in the RH and stores objects in a manner that produces viewpointdependent effects, whereas an abstract subsystem operates more effectively than a specific subsystem in the UI and does not store objects in a viewpoint-dependent manner.

Serotonin (5-HT) appears to modulate affective behaviours by providing a homeostatic threshold around which other transmitters respond. This general principle of activity should hold for other types of behaviour, including cognition, but has not been extensively examined. We hypothesized, based on past findings, that increased 5-HT would constrain prefrontally guided working memory functions that are mediated by catecholamine neurotransmitters. Healthy adults ingested amino acid compounds designed to deplete and load systemic tryptophan levels in a repeated-measures crossover design. Outcome variables included total plasma tryptophan, serum prolactin levels and self-report measures of mood, as well as measures of motor skill, attention, memory span and working memory for verbal, spatial and affective stimuli. Our findings indicate decrements in working memory for verbal and affective stimuli following tryptophan loading versus depletion, as well as subtle changes in vigilant attention and motor coordination. Implications for the aetiology and treatment of affective disorders and psychosis are discussed.