Memory for past events may be based on retrieval accompanied by specific contextual details (recollection) or on the feeling
that an item is old (familiarity) or new (novelty) in the absence of contextual details. There are indications that recollection,
familiarity, and novelty involve different medial temporal lobe subregions, but available evidence is scarce and inconclusive.
Using functional magnetic resonance imaging (MRI), we isolated retrieval-related activity associated with recollection, familiarity,
and novelty by distinguishing between linear and nonlinear oldness functions derived from recognition confidence levels. Within
the medial temporal lobes (MTLs), we found a triple dissociation among the posterior half of the hippocampus, which was associated
with recollection, the posterior parahippocampal gyrus, which was associated with familiarity, and anterior half of the hippocampus
and rhinal regions, which were associated with novelty. Furthermore, multiple regression analyses based on individual trial
activity showed that all three memory signals, i.e., recollection, familiarity, and novelty, make significant and independent
contributions to recognition memory performance. Finally, functional dissociations among recollection, familiarity, and novelty
were also found in posterior midline, left parietal cortex, and prefrontal cortex regions. This is the first study to reveal
a triple dissociation within the MTL associated with distinct retrieval processes. This finding has direct implications for
current memory models.