The neural mechanism of spatial-positional association in working memory: A fMRI study

In the last decade, research has reported that items at the beginning of a memorized sequence are responded to faster with the left hand, whereas items at the end are responded to faster with the right hand. This Spatial-Positional Associations of Response Codes effect has been extensively studied using behavioral methods. However, the neural networks underlying it remain unclear. We found using functional magnetic resonance imaging (fMRI) that the dorsal attention network was involved in spatial-positional associations, in particular a region of the right superior frontal cortex / pre-supplementary motor area (pre-SMA), within which neural activity correlated with behavioral measures of the strength of spatial-positional associations. Psychophysiological interaction (PPI) analysis revealed functional connectivity between this area and other regions of the dorsal attentional network including the SMA, and with the hippocampal-retrosplenial network. In contrast, explicit processing of serial order independent of spatial-positional associations was related to activity in the inferior parietal cortex. Our results provide new insight into positional coding theories of working memory, including the mental whiteboard hypothesis. They suggest that the behavioral effects of positional coding (congruency between hand and ordinal position within the list) are mediated through spatial and motor control maps in the dorsal attentional system.