Event-related potentials reveal topographical and temporal distinct neuronal activation patterns for spatial and object working memory

This study examined whether working memory processes for object and spatial information are associated with different patterns of ERP activity. Subjects performed two versions of a delayed match-to-sample task in which either object forms or two-dimensional spatial configurations (S1) had to be encoded and retained in working memory for 6800 ms for comparison with a subsequent stimulus (S2). Event-related potentials (ERPs) were recorded from 29 electrode sites in the S1-S2 interval. Negative slow wave activity in the ERP varied with both, the type of memory task and the amount of materials held in working memory. When spatial information was maintained in working memory negative slow wave activity rapidly rose at recording sites overlying posterior parietal and occipital cortical areas. At these recording sites, slow wave increased in amplitude with increasing spatial memory load. For object information, load-sensitive negative slow wave activity was obtained approximate to 2000 ms later than in the spatial task and it was focused to mid-frontal recording sites. Moreover, in the object memory task more pronounced negative slow wave activity was found at right inferior temporal recording sites indicating a larger involvement of the right temporal lobe in the processing of object as compared to spatial information. The results provide evidence for the notion that encoding and retention processes for object information and for spatial information can be functionally dissociated and involve differential patterns of neuronal activation rapidly shifting in time.