EEG gamma band is asymmetrically activated by location and shape memory tasks in humans.

From the viewpoint of psychology, it is thought that perception analysis of the visual world includes two information processes: global (whole) and local (part) processes. It is assumed that the global process is carried out in the right hemisphere, and the local process, in the left hemisphere. In the present study, gamma EEG band activities during location memory (LM) task, as a global form, and shape memory (SM) task, as a local form, were calculated from the temporal, parietal and occipital areas using stimuli consisting of categorical patterns of small shapes. Gamma band activity during the SM task was greater than that during the LM task. It was assumed that the SM task requires a higher memory load condition than the LM task. In terms of the laterality ratio obtained from the whole electrode array, the gamma band was significantly activated in the right hemisphere during the LM task, and in the left hemisphere during the SM task. The gamma activation in the occipital area was significantly high in the right hemisphere for both tasks. High gamma band activation was observed in the right parietal area during the LM task and in the left temporal area during the SM task. It was concluded that global and local information processes occur in the left temporal areas and in the right occipitoparietal areas, respectively. The results of this study are useful in the assessment of visual cognition deficits in patients with cerebral hemispheric lesions in the physical therapy.