Functional Connectivity of Specialized Occipitotemporal Cortical Regions

Cover

Background & Methods: A number of areas in the human occipitotemporal cortex (OTC) are specialized for processing particular types of sensory stimuli. These include the lateral occipital complex (LOC), an object-selective area; the fusiform face area (FFA), a face-selective area; the parahippocampal place area (PPA), a scene-selective area; and the extrastriate body area (EBA), a body part-selective area.1-7 Examining the commonalities and differences between the resting-state functional connectivity (rsFC) networks of the LOC, the EBA, the FFA and the PPA at rest should help elucidate the fundamental nature of functional specialization within occipitotemporal cortex.1-4,6,7

The imaging took place at CSI 3T Tim Trio scanner using advanced MRI sequences. RsFC networks (in healthy subjects) associated with EBA, FFA, PPA and LOC and differences in functional connectivity between these regions were assessed with advanced CPU-intensive network analysis techniques using the CSI-BITC advanced computing facility.

Figure 1

Results & Discussion: Advanced network analysis revealed interesting modular structure in the rsFC architecture (termed ‘graph’) of the OTC. EBA’s rsFC architecture graph segregates into three modules. The first of these (yellow in Figure1), 1-4,6,7containing the default mode network (DMN) and frontoparietal attention networks (FPAN), is uniquely connected with the EBA. The presence of a DMN module in the rsFC network of the EBA is consistent with studies that report greater activity of the EBA when viewing images of one’s own body as opposed to those of others’ bodies implying a role for self-referential processing in visual representation of bodies. EBA’s rsFC graph also contains a sensorimotor module, reflecting motor resonance: internal motor simulations that underlie understanding of others’ actions.The third module comprised occipital visual processing areas. In terms of laterality effects(see Cover Picture), EBA connectivity was strongly right-dominant, with right-hemisphere EBA (REBA) exhibiting stronger rsFC to a number of areas including DMN, FPAN, basal ganglia and thalamus. LEBA exhibited stronger rsFC with somatosensory and motor cortices, consistent with motor resonance leading to preferential engagement of contralateral sensorimotor areas.1-4,6,7

Figure 2

Examining differential functional connectivity between regions, FFA exhibited stronger rsFC compared to EBA and LOC in FPAN (Figure 2), indicating subjects paying higher attention to faces compared to non-face stimuli. On the other hand, FFA exhibited decreased rsFC to sensorimotor cortices, indicating reduced sensorimotor linkages to visual processing of faces compared to objects and bodies.1-4,6,7 Finally, rsFC networks change during task-related brain activity.5Baseline LEBA functional connectivity (Figure 3) to FPAN increased while at the same time DMN and sensorimotor networks decreased due to the increased attention demands of performing the task, compared to rest.

Figure 3

References: 1) Gopinath et al., Proc. SfN, 41:575.03, 2011; 2) Proc. ISMRM, 20:2015, 2012; 3) Proc. SfN, 42:285.01, 2012; 4) Proc. ISMRM, 21:2254, 2013; 5) Proc. ISMRM, 21:2273, 2013; 6) Proc OHBM, 19:1860, 2013; 7) Manuscript submitted to Neuroscience.