- A: The density of fibers can be quantified by counting the number of intersections with lines projected onto a terminal field. B: Representative coronal plot of neurons retrogradely labeled with differently labeled tract tracers injected at distinct locations within the insula of a macaque monkey. C: High-resolution T1-weighted anatomical scan (MDEFT) showing an injection site (light spot) of modified biocytin conjugated with gadolinium in the somatosensory cortex of a rat.
We use various neuroanatomical methods (quantitative hodology, in vivo tract tracing with MR contrast agents, allometry, and 3D-structural analysis) and combinations of neuroanatomical and functional methods (tract tracing combined with fMRI, or histology combined with optical imaging and electrophysiology) to examine the intricate connectivity of the brain, the correlation between histology and neuronal activity in the visual cortex, and the fine 3D organization of cortical microvasculature.
Neuroanatomy reveals the network structure within and between brain regions. Knowing the network structure is a fundamental prerequisite for understanding mechanisms behind brain functions. We investigate connectivity using four different approaches:
1) Quantitative connectivity in the cerebral cortex. This is a study on the cortico-cortical connectivity in the mouse  based on the anterograde tracer biotinylated dextran amine (Figure 1A). The study quantifies the rich connectivity of the cortex within itself and allows the development of a generalized model of horizontal connectivity in the cortex .
2) Anatomofunctional connectivity in the insular cortex in the macaque monkey. We combine high-resolution tract tracing (Figure 1B) with our department's advanced MRI and fMRI to examine the neuronal connections of the insular cortex in the macaque monkey. This examination contributes to our understanding of how the insula integrates bodily sensations with emotions – and how it might engender a sense of self awareness in humans.
3) In vivo connectivity using new contrast agents. Our chemists develop tracers (modified biocytin) which can be detected by magnetic resonance imaging (MRI) and which have some advantages over the previously used manganese [3,4]. Histological investigations in combination with MRI studies (Figure 1C) are in progress in order to see if the modified tracers are taken up and transported as efficiently as conventional biocytin.
4) Allometric study of the cerebral and the cerebellar cortex.The size of the cerebral and the cerebellar cortex increases indifferent ways with global brain size in different mammalian species. This phenomenon can be explained by the different network structure within the cerebral and cerebellar cortex.