Multimodal imaging of human early visual cortex by combining functional and molecular measurements with fMRI and PET

Receptor distribution patterns of neurotransmitters and distinct functional fields of the human brain appear to be tightly connected with respect to their topological allocation along the cerebral cortex. There is, however, considerable lack of human data directly demonstrating this association in vivo. Here, we assessed the relationship between the distribution of the major inhibitory serotonergic neurotransmitter receptor, the 5-HT(1A) subtype, and the functional organization within early visual cortex defined by retinotopic mapping. The 5-HT(1A) receptor-binding potential was quantified by positron emission tomography (PET) using the highly selective and specific radioligand [carbonyl-(11)C]WAY-100635 in seven healthy subjects. The retinotopic maps and borders determined by functional magnetic resonance imaging (fMRI) were compared to the receptor distribution employing surface-based region of interest analysis in each of these subjects. We found a significant difference in receptor-binding potential in the functionally defined primary (V1) compared to secondary (V2) visual area, as V1 exhibits only 68% of receptor binding found in V2 in both hemispheres, which is consistent with postmortem data. Our in vivo findings clearly support prior assumptions of a link between receptor distribution and functional fields of the human cortex.