Activation Shift from Medial to Lateral Temporal Cortex Associated with Recency Judgements Following Impoverished Encoding

Recency judgements can be performed on the basis of across-event relational information that directly provides temporal order among past events. Non-relational item-based information internal to individual past events, such as information retrieved through familiarity, may also contribute to recency judgements. The present functional magnetic resonance imaging study examined neural substrates for item-based processing during recency judgements as an alternative to relational recency judgements. One half of word stimuli were encoded relationally prior to recency judgements, and the relational encoding of the other half was hampered such that the words were processed relatively in an item-based manner. Brain activity in the medial temporal lobe was observed during recency judgements for words studied with relational memory processing, whereas brain activity in the lateral temporal cortex was observed during recency judgements for words studied relatively in an item-based manner. It was revealed further that recognition of individual words per se, which can also be regarded as familiarity/recency judgements but is non-relational in nature, also activated the lateral temporal region. These results indicate multiple routes for recency judgements within the temporal lobe that are recruited depending on how past episodes are represented and retrieved for judgements of their temporal order.