Hyperactivation of parahippocampal region and fusiform gyrus associated with successful encoding in medial temporal lobe epilepsy

Purpose: Performance in recognition memory differs among patients with medial temporal lobe epilepsy (MTLE). We aimed to determine if distinct recognition performances (normal vs. impaired) could be related to distinct patterns of brain activation during encoding. Methods: Event‐related functional magnetic resonance imaging (fMRI) activation profiles were obtained during successful encoding of non–material‐specific items, in 14 MTLE patients tested for recognition of stimuli afterward. Findings were compared to those of 25 healthy subjects, and voxel‐based correlations were assessed between brain activation and performance. Key Findings: Patients with left and right MTLE showed similar activations and similar performances. As a whole, the group of patients demonstrated altered recognition scores, but three of the seven patients with left MTLE and three of the seven patients with right MTLE exhibited normal performance relative to controls. In comparison to healthy subjects and patients with impaired recognition, patients with normal recognition showed weaker activations in left opercular cortex, but stronger activations in bilateral parahippocampal region/fusiform gyrus (PH/FG). By contrast, patients with impaired performance showed weaker activations in bilateral PH/FG, but stronger activations in a frontal/cingulate and parietal network. Recognition performance was correlated positively to bilateral PH/FG activations, and negatively correlated to bilateral frontal/cingulate activations, in the whole group of patients, as well as in subgroups of patients with either left or right MTLE. Significance: These results suggest occurrence of effective functional compensation within bilateral PH/FG in MTLE, allowing patients to maintain recognition capability. In contrast, impairment of this perceptive–memory system may lead to alternative activation of an inefficient nonspecific attentional network in patients with altered performance.