There is accumulating evidence for sensory processing deficits in the visual system, which can also be measured by ERP. P300, traditionally a measure of higher order cognitive processing, was recently shown [13] to be also strongly related to early sensory processing, as measured by MMN. In a double-blind, randomized ketamine challenge experiment [14], a visual oddball task known to generate P300 was tested. Ketamine led to a reduction in P300 amplitude, which was associated with a reduced fMRI response that was primarily seen in visual sensory areas. Similarly to the auditory experiment, differences in the frontal cortex were much less pronounced.
