Neural Coding of Color

We measured multi-channel MEG (MagnetoEncephaloGraphy) responses to a set of color stimuli (for twelve colors). Subjects are gazing at colored squares during the measurements. Each ECD (Estimated Current Dipole) in the brain, thus localized response to the corresponding color stimulus, is moving inside area V4α (BARTELS and ZEKI, 2000), showing a characteristic orbital path. In our measurements, absolute positional- errors are still large. However, the relative resolution is quite high, since the orbits of ECDs are localized in quite a small volume (1 (cm 3 )). This localized volume corresponds to V4α. ECDs in the volume are forming different orbits from each other. V4α conserves topological relation in the chromatic coordinate. Our results suggest that the neural coding of chromaticity topologically corresponds to well known geometrical coding of chromaticity in terms of a continual deformation between neighboring representations. Therefore, the observations could be interpreted as that the chromatic topology is represented in V4α and that the refined coding of each color is spatiotemporally represented within V4α. This fine spatiotemporal resolution in the results is obtained by our non-parametric gICA (geometric Independent Component Analysis) algorithm based on the isotropy condition of connections among adjacent tangential spaces in the neural activities.