Towards a solution for performance related confounds: frontal, striatal and parietal activation during a continuous spatiotemporal working memory manipulation task.

Working memory plays a role in various forms of psychopathology. However, working memory consists of multiple theoretical components that may be differently taxed by various specific types of task, and brain activation differences between patients and healthy controls may result from differences in task performance. This makes it difficult to interpret such results in terms of disease-related dysfunctions in affected regions or networks. The aim of the current study was to determine the brain activation related to the updating of spatiotemporal content of working memory, in such a way that performance-related confounds in future clinical studies would be minimized. Nineteen healthy volunteers performed a task involving a continuous updating process during fMRI measurement. A frontostriatal network including medial and lateral prefrontal cortex, inferior frontal cortex, premotor cortex, supplementary motor cortex, thalamus and putamen was found to be related to the updating process. The results constrain the set of brain regions plausibly related to the specific updating component of working memory. Further, the task design may be of use in future studies of pathological conditions such as schizophrenia due to the minimization of potential confounds.

Prefrontal, parietal and basal activation associated with the reordering of a two-element list held in working memory.

A functional specialization in the prefrontal cortex along a dorsal-ventral gradient according to the type of processing in working memory, i.e. manipulation vs. maintenance, has been proposed based on previous neuroimaging studies. This seems particularly important for the further understanding of the functional architecture underlying working memory problems in patient populations. The current study examines the prefrontal involvement in the maintenance and manipulation of serial order of elements in working memory, with a task designed to be as simple as possible, to the aim of possible uses in clinical studies. Subjects held two-element ordered lists in memory and were presented with pseudo-random sequences of "reorder" and "maintain" cues. Reorder cues were found to be associated with activation in the dorsal prefrontal cortex, parietal cortex and the basal ganglia. The results show that the simple task was indeed sufficient to evoke the prefrontal activation of interest, add to the information on functional dorsal-ventral specialization in prefrontal cortex and provide support for a prefrontal-parietal monitoring-manipulation network.