Live-Imaging of Myelin in Animal Models and in Human.

The pioneer work of Paul Broca (1824-1880) was the first demonstration that brain is functionally not homogeneous, but on the contrary constituted by the assembly of different areas each responsible for specific function. Investigating aphasic patients Broca described a small area in the left frontal lobe, which he described as responsible for articulate language [1, 2]. This region is now known as Broca’s area. Since then the localizationism theory has extended and in association to the long-life concept that only neurons were true functional cells, it has generally been assumed that each brain function is driven by some groups or subpopulation of neurons. As a consequence, any neurological dysfunction had to be attributed to the lesion of a subgroup of neuronal cell. One of the most puzzling situation had been reached by Gerstmann’s syndrome, a condition where a small lesion localized in the dominant inferior parietal lobe results in the association of four apparently completely unrelated symptoms: dysgraphia/agraphia dyscalculia/acalculia, finger agnosia, and left-right disorientation. First described in 1924 by Joseph Gerstmann [3, 4] this syndrome has stirred a controversy for over 80 years among neurologists questioning which population of cortical neurons localized in the angular and supramarginal gyrus could be responsible for such a diversity of cognitive functions. It is only very recently with the development of