Magnetoencephalographic--features related to mild cognitive impairment.

We recorded changes of brain activity from 10 MCI patients and 10 controls related to shallow (nonsemantic) and deep (semantic) word encoding using a whole-head MEG. During the following recognition tasks, all participants had to recognize the previously encoded words, which were presented again together with new words. In both groups recognition performance significantly varied as a function of depth of processing. No significant differences were found between the groups. Reaction times related to correctly classified new words (correct rejections) and incorrectly classified repetitions (misses) of MCI patients showed a strong tendency toward prolongation compared to controls, although no statistically significant differences occurred. Strikingly, in patients the neurophysiological data associated with nonsemantic and semantic word encoding differed significantly between 250 and 450 ms after stimulus onset mainly over left frontal and left temporal sensors. They showed higher electrophysiological activation during shallow encoding as compared to deep encoding. No such significant differences were found in controls. The present results might reflect a dysfunction with respect to shallow encoding of visually presented verbal information. It is interpreted that additional neural activation is needed to compensate for neurodegeneration. This finding is suggested to be an additional tool for MCI diagnosis.