Dissociable parietal systems for primacy and subsequent memory effects

The frequently observed superior memory for the first items on a list is referred to as primacy. The aetiology of this effect in terms of cognitive processes and their neural substrate is subject to an ongoing debate. However, the brain areas generally involved in successful encoding are well described by subsequent memory studies in which activity during encoding is correlated with memory performance. We employed an object-location association paradigm to differentiate the neural correlate of the primacy from the subsequent memory effect. Activity in the intraparietal sulcus predicted memory performance across all encoding positions. Increased activity in the inferior parietal lobe and angular gyrus resulted exclusively in a more efficient encoding of the first item presented. These areas are part of the ventral frontoparietal network involved in stimulus driven attention. Our results implicate the relatively elevated attention to the first item probably due to its contextual distinctiveness, as a major contributor to the primacy effect.