Distinct brain networks coupled with the parietal cortex represent target location inside and outside the visual field

Our mental representation of the egocentric space is influenced by the disproportionate sensory perception along the ventral-dorsal (i.e., front-back) axis of the body. Previous studies typically investigated the neural architectures involved in the egocentric representations within the visual field and revealed a crucial involvement of the parietal cortex and its interaction with the frontal lobe. However, neural architectures involved in the space representation behind self-body are still unclear. To address this problem, we applied both functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) to a 3D spatial-memory paradigm for human participants, in which the participants remembered a target location within (left or right) or outside (back) their visual field. Both fMRI and MEG experiments showed that the involvements of the fronto-parietal network including the frontal eye field and supplementary motor area were larger in the representations of retrieved target object within the visual field than outside. Conversely, the medial temporal lobe (MTL)-parietal network, including the right entorhinal cortex, was more involved in the target representation when the target was outside the visual field in both the experiments. In the MEG experiment, the connectivity increased in alpha-band frequency (8-13 Hz) in both fronto-parietal and MTL-parietal networks, and the preferential enhancement of the MTL-parietal network for the back preceded that of the fronto-parietal network for left/right. These findings suggest that the parietal cortex may represent whole space around self-body by coordinating the two distinct brain networks to process the egocentric spatial representation inside and outside the visual field.