Our studies indicate that different visual areas in the brain may communicate via temporally modulated messages. We showed previously that neurons in different areas of the brain encode and transmit information about stationary, two-dimensional pictures that vary in form, brightness, and duration. We also showed that information about remembered visual features was also carried by a temporal code. Now we have extended those studies to show that neurons in visual cortex (areas V1, V2, and V4) carry information about the form, color, luminance, and size of a stimulus in a temporally modulated code. Our results suggest that cortical neurons are able to convey information about many different features without confounding them. The mechanism for encoding these multiple messages uses temporal modulation to multiplex the different messages on the neuron's response in a separable way. Our recent work has found candidate response waveforms that act as the temporal codes with which the brain represents the visual features of form and color. These codes are very similar for different cells within a visual area, across different visual areas, and in different monkeys. This finding suggests that the temporal codes used by the brain might be invariant and universal. It has been proposed that color and form information is divided into separate channels (e.g., cytochrome oxidase blob and interblob regions) in the cortex. In a visual discrimination task studying the encoding of color and form information in cortical neurons, we showed that information about color and pattern rises over time in all neurons in cortical areas V1-V4. Such a result is not consistent with the idea that information about form and color is grouped into separate """"""""channels"""""""" in cortex but rather suggests that all neurons participate in visual processing, irrespective of the type of visual parameter involved.
