Cortical interactive network during mental rotation of Chinese character

Mental rotation (MR) of Chinese characters has been proposed to employ distinct strategies depending on task difficulty. Cognitive process in MR is associated with multi-component neural networks, and elucidation of specific cortical interactions taking place during MR will assist understanding of the cognitive processes involved. In this study, we investigated cortical interactive networks involved in Chinese character MR tasks of different difficulties. Scalp electroencephalogram (EEG) signals were recorded from nine subjects (male/female=6/3) during MR of a Chinese character presented at different orientations (0 degrees, +/-60 degrees, +/-120 degrees and 180 degrees). Partial directed coherence (PDC) analysis based on multivariate Granger causality (GC) was used to assess cortical interactions. At +/-60 degrees and +/-120 degrees, lateral interactions from right to left counterparts were found in both the parietal and motor-related areas, and they were enhanced with the increase of rotation angle. The main interactions between parietal and motor-related areas showed feedforward at rotations of +/-60 degrees and +/-120 degrees, while feedback interactions appeared at rotations of +/-120 degrees. However, at 180 degrees of rotation, neither lateral interactions within motor-related areas nor feedback interactions from motor-related to parietal areas were found. These findings show that during MR of Chinese character (1) cortical interactive networks change according to task difficulty, and (2) the right hemisphere plays an initiating role in bilateral cortical activation.