Engagement of the Medial Temporal Lobe in Verbal and Nonverbal Memory: Assessment with Functional MR Imaging in Healthy Subjects

The hippocampus and parahippocampal gyrus have a central role in the acquisition of new memories. Although functional MR imaging (fMRI) can provide information on the functional status of these brain regions, it has not reached widespread use in the presurgical assessment of patients undergoing temporal lobectomy. We aimed to evaluate whether simple memory-encoding paradigms could be used to elicit robust activations in the hippocampus and parahippocampal gyrus and to determine the lateralization of verbal and nonverbal memory. We also studied the relative contribution of the anterior and posterior portions of these structures. We conducted this study on 16 healthy subjects by performing event-related fMRI using 3 memory encoding tasks with words, objects, and faces. In addition to a second-level group analysis, region-of-interest (ROI)-based measurements of the signal intensity percent change and of the percentage of activated voxels, determined at 2 thresholds, were performed. ROIs were drawn on the hippocampus and parahippocampal gyrus, divided into anterior and posterior segments. We found overall left-lateralized activation with words, bilateral activation with objects, and right-lateralized activation with faces. In particular, significant hippocampal activations were observed with all 3 categories of stimuli, and the head of the hippocampus was generally more engaged than its body and tail. Data on the signal intensity percent change and percentage of activated voxels are provided for each ROI and task. The combination of these 3 undemanding memory tasks could be considered, following appropriate validation, as a tool to assess the functional status of the medial temporal lobe in clinical settings.