The posterior parietal cortex: comparing remember/know and source memory tests of recollection and familiarity

Numerous neuroimaging studies have shown a dissociation within the left posterior parietal cortex (PPC) between recollection and familiarity, with dorsal regions routinely active during familiarity and ventral regions active during recollection. The two most common methods for separating the neural correlates of these retrieval states are the remember/know paradigm and tests probing source memory. While relatively converging results have been found using these methods, the literature is lacking an adequate and direct comparison of the two procedures. We directly compared these two methodologies and found differences in both the magnitude and extent of activation within the left PPC. During familiarity, dorsal PPC regions were more strongly activated by the source test, while the remember/know test led to stronger recollection-related activations within the ventral regions of the PPC. This modulation of PPC activity is particularly important because it suggests that the neural correlates of familiarity and recollection depend on how they are operationalized. Previous assumptions that remember/know and source memory tests are functionally equivalent should therefore be re-evaluated. Additionally, any theories attempting to explain the functional role of the PPC during memory retrieval must take these differences into account.