Performance in recognition memory is correlated with entorhinal/perirhinal interictal metabolism in temporal lobe epilepsy

In addition to the hippocampus, the entorhinal/perirhinal cortices are often involved in temporal lobe epilepsy (TLE). It has been proposed that these anterior parahippocampal structures play a key role in recognition memory. We studied the voxel-based PET correlation between number of correctly recognized targets in a new recognition memory paradigm and interictal cerebral metabolic rate for glucose, in 15 patients with TLE with hippocampal sclerosis. In comparison to healthy subjects, patients had decreased recognition of targets (P < 0.001) and ipsilateral hypometabolism (relative to side of hippocampal sclerosis) of the hippocampus, entorhinal/perirhinal cortices, medial temporal pole, and middle temporal gyrus (P < 0.05, corrected by false discovery rate method). Performance correlated with interictal metabolism of ipsilateral entorhinal/perirhinal cortices (P < 0.005, Spearman's rank test), but this relationship was not significant in the hippocampus itself (P > 0.18, Spearman's rank test). These findings highlight the preferential involvement of entorhinal/perirhinal cortices in recognition memory in patients with TLE, and suggest that recognition memory paradigms may be useful in assessing anterior parahippocampal functional status in TLE.

Research Highlights
► In temporal lobe epilepsy, performance in recognition memory is correlated with interictal metabolism of entorhinal/perirhinal cortex, and not with that of hippocampus.
► The preferential metabolic involvement of the entorhinal/perirhinal cortices may be related to the preferential involvement of these structures in the epileptogenic network of patients with temporal lobe epilepsy and impaired performance in recognition memory.
► Recognition memory paradigms may be useful in assessing anterior parahippocampal functional status in temporal lobe epilepsy.