Salle Langevin, 29 rue d'Ulm, 75005 Paris
We all appreciate substantial differences among our friends and colleagues in their cognitive ability and style. Such variability introduces a rich diversity of culture and lifestyle into our society. Importantly, individual differences can be used as a source of information that links brain structure to cognitive functions, functional differences of a brain region across individuals can be detected as systematic variation of regional gray matter volume and white matter microstructure using voxel-based morphometry (VBM) and diffusion tensor imaging (DTI), respectively (Kanai & Rees 2011). In this talk, I will show how this approach can be applied to identify the brain structure that determines the dynamics of perceptual rivalry. Our VBM and DTI results show that anterior and posterior parts of intraparietal sulcus (IPS) play distinct roles in perceptual rivalry. VBM shows that individuals with fast switch rate exhibited greater gray matter volume in posterior IPS, whereas slow switchers had greater anterior IPS. Fractional anisotropy (FA) values derived from DTI show that the white matter integrity beneath these regions correlated with perceptual switch rate. We complemented the correlational nature of these analyses by confirmatory TMS experiments and thereby established causal involvement of these regions in perceptual rivalry. These results together suggest that perceptual rivalry reflects a balance between top-down sustention of a current percept by anterior IPS and monitoring of possibly conflicting sensory evidence by posterior IPS. Finally, I will discuss the application of this approach in real life situations. In contrast to functional neuroimaging, structural neuroimaging does not require a virtual environment that emulates cognitive and social tasks motivated by real life situations. Instead, brain structure information can be directly linked to behaviors observed in real life. I will provide a few examples in which variability in brain structure has been linked to everyday behaviors such as attentional distractibility, loneliness and online social networks. This opens a new possibility to investigate brain functions from the perspective of everyday behavioral data by introducing fieldwork to cognitive neuroscience.