Collaborative activity between parietal and dorso-lateral prefrontal cortex in dynamic spatial working memory revealed by fMRI

Functional MRI was used to determine how the constituents of the cortical n etwork subserving dynamic spatial working memory respond to two types of in creases in task complexity. Participants mentally maintained the most recen t location of either one or three objects as the three objects moved discre tely in either a two- or three-dimensional array. Cortical activation in th e dorsolateral prefrontal (DLPFC) and the parietal cortex increased as a fu nction of the number of object locations to be maintained and the dimension ality of the display. An analysis of the response characteristics of the in dividual voxels showed that a large proportion were activated only when bot h the variables imposed the higher level of demand. A smaller proportion we re activated specifically in response to increases in task demand associate d with each of the independent variables. A second experiment revealed the same effect of dimensionality in the parietal cortex when the movement of o bjects was signaled auditorily rather than visually, indicating that the ad ditional representational demands induced by 3-D space are independent of i nput modality. The comodulation of activation in the prefrontal and parieta l areas by the amount of computational demand suggests that the collaborati on between areas is a basic feature underlying much of the functionality of spatial working memory. (C) 2000 Academic Press.