Categorical and coordinate spatial relations in working memory: an fMRI study.

Spatial relations within and between objects can be represented either coordinately or categorically. Coordinate representations concern metric and precise relations, and are strongly associated with right parietal cortex activity, while categorical representations relate to more qualitative, abstract relations, and have shown to have a, somewhat weaker, relationship with left parietal cortex activation [Trojano et al., 2002. Coordinate and categorical judgements in spatial imagery. An fMRI study. Neuropsychologia, 40, 1666-1674]. In the current study, a functional magnetic resonance imaging (fMRI) experiment enabled a closer examination of this proposed hemispheric lateralization within a working memory paradigm. A visual half field task in a match-to-sample format was conducted to examine these lateralization effects with a short (500 ms) and a long (2000 ms) interval between two stimuli, with either a categorical or a coordinate instruction. In the behavioural data, the hypothesized hemispheric specialization was found for the brief interval. The imaging data support the hemispheric lateralization as well. The proposed lateralization effect is present during spatial relation processing, but only within the superior parietal cortex and with certain temporal constraints. Additionally, categorical trials show a clear involvement of the left and right premotor and posterior parietal areas during the brief interval, while coordinate trials are related to higher activity in the left and right insula, during the long interval. We propose a refined view on lateralization of spatial relation processing, keeping in mind the temporal restrictions shown by this study.