Adaptive visual memory reorganization in right medial temporal lobe epilepsy.
OBJECTIVE
We investigated functional reorganization mechanisms of the human medial temporal lobe (MTL) for episodic memory, in patients suffering from medial temporal lobe epilepsy (MTLE) with hippocampal sclerosis (HS).


METHODS
We used functional magnetic resonance imaging (fMRI) to measure brain activity changes during matched episodic encoding tasks of abstract words (Verbal) and line drawings (Visual), in patients with unilateral right MTLE undergoing presurgical evaluation and healthy controls.


RESULTS
As expected, a significant interaction between material type and the side of MTL activity was present in the control group, with preferential involvement of the left hippocampus in verbal encoding and the right parahippocampal region in visual encoding. When compared with controls, right MTLE patients with intact performance activated a region in the left hippocampus more during visual encoding, which resulted in an interaction between group and hemisphere. Importantly, an effect of memory performance on visual encoding activity was observed in the patients, with greater engagement of the left MTL being associated with higher recognition scores. Interestingly, activity in the left MTL also depended on the epileptic seizure frequency, suggesting a role for this clinical parameter in the recruitment of contralateral regions.


CONCLUSIONS
Taken together, these results indicate functional reorganization of the MTLs in right HS, through transfer of function from the right to the left hemisphere, and strongly suggest an adaptive role for such reorganization mechanism in supporting preserved visual memory.
Figueiredo
Patrícia
P
IBILI, Department of Biophysics, Faculty of Medicine, University of Coimbra, Coimbra, Portugal. pfigueiredo@fisica.ist.utl.pt
Santana
Isabel
I
Teixeira
João
J
Cunha
Catarina
C
Machado
Egídeo
E
Sales
Francisco
F
Almeida
Eduarda
E
Castelo-Branco
Miguel
M
D000222:Adaptation, Physiological; D000328:Adult; D004833:Epilepsy, Temporal Lobe / Q000150:complications* / Q000175:diagnosis / Q000503:physiopathology; D005260:Female; D007839:Functional Laterality; D006624:Hippocampus / Q000503:physiopathology; D006801:Humans; D008297:Male; D008569:Memory Disorders / Q000175:diagnosis / Q000209:etiology* / Q000628:therapy*; D009483:Neuropsychological Tests; D012720:Severity of Illness Index; D014705:Verbal Behavior; D014796:Visual Perception