The clinical and functional measurement of cortical (in)activity in the visual brain, with special reference to the two subdivisions (V4 and V4 alpha) of the human colour centre

We argue below that, at least in studying the visual brain, the old and sim ple methods of detailed clinical assessment and perimetric measurement stil l yield important insights into the organization of the visual brain as a w hole, as well as the organization of the individual areas within it. To dem onstrate our point, we rely especially on the motion and colour systems, em phasizing in particular how clinical observations predicted an important fe ature of the organization of the colour centre in the human brain. With the use of data from functional magnetic resonance imaging analysed by statist ical parametric mapping and independent component analysis, we show that th e colour centre is composed of two subdivisions, V4 and V4 alpha, the two t ogether constituting the V4 complex of the human brain. These two subdivisi ons are intimately linked anatomically and act cooperatively The new eviden ce about the architecture of the colour centre might help to explain why th e syndrome, cerebral achromatopsia, produced by lesions in it is so variabl e.