Differential Connectivity Within the Parahippocampal Place Area
54.24, Tuesday, May 14, 2:30 - 4:15 pm, Royal Ballroom 4-5
Christopher Baldassano1, Diane M. Beck2, Li Fei-Fei1; 1Department of Computer Science, Stanford University, 2Beckman Institute and Department of Psychology, University of Illinois at Urbana-Champaign
The Parahippocampal Place Area (PPA) has traditionally been considered a homogeneous region of interest, but recent evidence from both human studies and animal models has suggested that PPA may be composed of functionally distinct subunits. Macaque parahippocampal cortex exhibits distinctive changes in connectivity along the anterior-posterior axis, suggesting that anterior and posterior segments of human PPA might also have differential connectivity properties. To investigate this hypothesis, we utilize a functional connectivity measure for fMRI that can estimate connectivity differences at the voxel level. Applying this method to whole-brain data from two experiments, we provide the first direct evidence that anterior and posterior PPA exhibit distinct connectivity patterns. Anterior PPA is more strongly connected to regions in the default mode network, including the parieto-medial temporal pathway consisting of the caudal Inferior Parietal Lobule (cIPL) and Retrosplenial Cortex (RSC). Posterior PPA is more strongly connected to occipital visual regions, including the Lateral Occipital Complex (LOC) and the Transverse Occipital Sulcus (TOS). We further show that object sensitivity in PPA also has an anterior-posterior gradient, with stronger responses to images of abstract sculptures in posterior PPA than in anterior PPA. Our findings not only reinforce the link between PPA and macaque parahippocampal regions, but also demonstrate that PPA is actually composed of at least two regions operating on different types of visual information, shedding new light on the controversy over its functional properties.