A New Code for Contrast in the Primate Visual Pathway

Chris Tailby, Samuel G. Solomon, Neel T. Dhruv, Najib J. Majaj, Sach H. Sokol, Peter Lennie
The Journal of Neuroscience, April 4, 2007, 27(14):3904-3909;

We characterize a hitherto undocumented type of neuron present in the regions bordering the principal layers of the macaque lateral geniculate nucleus. Neurons of this type were distinguished by a high and unusually regular maintained discharge that was suppressed by spatiotemporal modulation of luminance or chromaticity within the receptive field. The response to any effective stimulus was a reduction in discharge, reminiscent of the "suppressed-by-contrast" cells of the cat retina. To a counterphase-modulated grating, the response was a phase-insensitive suppression modulated at twice the stimulus frequency, implying a receptive field comprised of multiple mechanisms that generate rectifying responses. This distinctive nonlinearity makes the neurons well suited to computing a measure of contrast energy; such a signal might be important in regulating sensitivity early in visual cortex.

Fulltext: http://www.jneurosci.org/cgi/reprint/27/14/3904