Abstract
The brain encodes targets for reaching in egocentric (EGO) and/or allocentric (ALLO) reference frames (Byrne and Crawford 2010). Differences in the cortical activation, but not functional organization, of these two representations have been described (Chen et al., 2014; Neggers et al., 2006). Based on previous findings, we expected increased integration & hubness in the ventral visual stream in ALLO brain networks. Here, we performed a secondary analysis of an event-related fMRI task (Chen et al., 2014). The paradigm consisted of 3 tasks with identical stimulus display but different instructions: remember absolute target location (EGO), remember target location relative to a visual landmark (ALLO), and a nonspatial control, color report. We performed a graph theoretical analysis (GTA) on contrast reduced, time-series data during the memory delay period. GTA measures, including the hubness, clustering coefficient, and efficiency were found, as well as the organization of the network into modules. Dynamical measures of network connectivity (synchrony and complexity) were quantified for individual task modules. EGO and ALLO brain networks showed increased functional segregation & integration, relative to control. Contrary to expectations, there were no inferotemporal modules in both tasks, rather the network was largely segregated into occipito-dorsal-parietal (ODP) and & temporo-frontal (TF) networks modules. The ALLO network demonstrated significantly higher modularity and hubs in the ODP module, relative to the EGO network. When the subtracting the common baseline correlation, the EGO showed segregation of occipital brain areas from the OPD module, but ALLO did not. Our results demonstrate that rather than increased ALLO encoding of visual reach targets in the ventral stream, there is increased specialization in the interaction between early visual brain areas and dorsal parietal brain areas. There was also increase in desynchronization & complexity in the OPD module, in the ALLO task, indicating an increase in difficulty of information processing.