Differential contributions of the hippocampus and rhinal cortices to verbal memory in epilepsy.

The present study explored the left mesial temporal lobe correlates of verbal memory in patients with temporal lobe epilepsy (TLE). An index of structural integrity, T2 relaxation time, was measured bilaterally in three mesial temporal regions of interest, and correlated with measures of verbal memory. The acquisition of verbal arbitrary relational material was most strongly associated with left perirhinal T2 signal. In contrast, verbal memory consolidation was related to T2 signal in the left hippocampus. Our findings suggest a key role for the left perirhinal region in the uptake of arbitrary linkages that underlie new learning. The hippocampus, on the other hand, is important for protecting newly learned information from the effects of interference. This double dissociation provides a neurocognitive account of the left mesial temporal memory syndrome.