Encoding and immediate retrieval tasks in patients with epilepsy: a functional MRI study of verbal and visual memory

Publication date: Available online 1 March 2018
Source:Journal of Neuroradiology
Author(s): Najat Saddiki, Sophie Hennion, Romain Viard, Nassima Ramdane, Renaud Lopes, Marc Baroncini, William Szurhaj, Nicolas Reyns, Jean Pierre Pruvo, Christine Delmaire
PurposeMedial lobe temporal structures and more specifically the hippocampus play a decisive role in episodic memory. Most of the memory functional magnetic resonance imaging (fMRI) studies evaluate the encoding phase; the retrieval phase being performed outside the MRI. We aimed to determine the ability to reveal greater hippocampal fMRI activations during retrieval phase.Materials and methodsThirty-five epileptic patients underwent a two-step memory fMRI. During encoding phase, subjects were requested to identify the feminine or masculine gender of faces and words presented, in order to encourage stimulus encoding. One hour after, during retrieval phase, subjects had to recognize the word and face. We used an event-related design to identify hippocampal activations.ResultsThere was no significant difference between patients with left temporal lobe epilepsy, patients with right temporal lobe epilepsy and patients with extra-temporal lobe epilepsy on verbal and visual learning task.For words, patients demonstrated significantly more bilateral hippocampal activation for retrieval task than encoding task and when the tasks were associated than during encoding alone. Significant difference was seen between face encoding alone and face retrieval alone.ConclusionsThis study demonstrates the essential contribution of the retrieval task during a fMRI memory task but the number of patients with hippocampal activations was greater when the two tasks were taken into account.



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