Temporal dynamics of medial temporal lobe activation during encoding and recognition. A magnetoencephalography study

The goal of this study was to examine the spatiotemporal profiles of medial temporal lobe (MTL) activation during encoding and recognition of word and picture stimuli. Activation profiles were obtained from 13 neurologically intact volunteers using whole-head Magnetic Source Imaging. While a clear preponderance of left MTL activation was noted during word encoding, and to a lesser extent during word recognition, the profile of activation during picture processing was more variable featuring greater right hemisphere contribution. This conclusion was supported by the finding of a positive correlation between the degree of right MTL activity and performance during the picture encoding task, and a negative correlation between the degree of activity in this region and accuracy of word recall. Timing data indicated that left MTL engagement in word encoding is more prominent during late processing of the stimuli, whereas left MTL activity during recognition shows an early peak soon after stimulus onset. Key words: memory, medial temporal lobe, magnetoencephalography, magnetic source imaging, encoding, recognition, functional brain imaging.