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Unlike tasks in which practice leads to an automatic stimulus-response association, it is thought working memory (WM) tasks continue to require cognitive control processes after repeated performance. Previous studies investigating WM task repetition are in accord with this. However, it is unclear whether changes in neural activity after repetition imply alterations in general control processes common to all WM tasks or are specific to the selection, encoding and maintenance of the relevant information. In the present study, functional magnetic resonance imaging (fMRI) was used to examine changes during sample, delay and test periods during repetition of both object and spatial delayed recognition tasks. We found decreases in fMRI activation in both spatial and object-selective areas after spatial WM task repetition, independent of behavioral performance. Few areas showed changed activity after object WM task repetition. These results indicate that spatial task repetition leads to increased efficiency of maintaining task-relevant information and improved ability to filter out task-irrelevant information. The specificity of this repetition effect to the spatial task suggests a difference exists in the nature of the representation of object and spatial information and that their maintenance in WM is likely subserved by different neural systems.

In order to ascertain whether the neural system for auditory working memory exhibits a functional dissociation for spatial and nonspatial information, we used functional magnetic resonance imaging and a single set of auditory stimuli to study working memory for the location and identity of human voices. The subjects performed a delayed recognition task for human voices and voice locations and an auditory sensorimotor control task. Several temporal, parietal, and frontal areas were activated by both memory tasks in comparison with the control task. However, during the delay periods, activation was greater for the location than for the voice identity task in dorsal prefrontal (SFS/PreCG) and parietal regions and, conversely, greater for voices than locations in ventral prefrontal cortex and the anterior portion of the insula. This preferential response to the voice identity task in ventral prefrontal cortex continued during the recognition test period, but the double dissociation was observed only during maintenance, not during encoding or recognition. Together, the present findings suggest that, during auditory working memory, maintenance of spatial and nonspatial information modulates activity preferentially in a dorsal and a ventral auditory pathway, respectively. Furthermore, the magnitude of this dissociation seems to be dependent on the cognitive operations required at different times during task performance.

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