Evaluation of neural networks in the brain during word silent reading/recalling by magnetoencephalographic imaginary coherence analysis

Abstract

Recent studies of the neural network for language function have revealed the existence of various networks such as superior longitudinal fasciculus and inferior frontooccipital fasciculus in addition to arcuate fibers connecting the anterior language area (Broca’s area) and the posterior language area (Wernicke’s area). In particular, the posterior language area has many fiber connections in the frontal, parietal, and temporal lobes. Previous studies using magnetoencephalography (MEG) have shown that beta and low gamma activities could be detected in the anterior language area in the left inferior frontal gyrus during silent reading and word recall tasks. However, detecting activity in the posterior language area has not been fully elucidated. Therefore, in this study, we investigated the imaginary coherence (IC) of the functional area with a whole-head MEG system during silent reading or word recall. In the silent reading tasks, the anterior part of the left frontal lobe and posterior part of the left temporal lobe showed high connectivity with the anterior language area, especially in the beta band and the low gamma bands. In the high gamma band, the connection with the motor area was strengthened. Areas with high connectivity with the posterior language area were found in the frontal lobe and the temporal lobe in the all bands. However, the relevant areas within these lobes were wide, and the specificity was unclear. In the word recall task, an area with high connectivity with the anterior language area was confirmed especially in the posterior superior temporal gyrus in the low gamma band. Areas with high connectivity with the posterior language area were found in surrounding areas and nonspecific parts of the frontal lobe in various bands. Though differences in language function networks between the anterior and posterior language areas were common, various patterns were revealed in each subject. This implies the importance of individual analysis in clinical evaluations. Imaginary coherence may be an effective way to detect activity in the posterior language area during silent reading and word recall tasks. Furthermore, the ease of performing the silent reading task makes it clinically applicable.