We study the general question of how visual information is transformed between the lateral geniculate nu-cleus of the thalamus (LGN) and layer 4 of the primary visual cortex. LGN cells receive visual input from one eye and are not sensitive to an object's orientation or direction of movement. Cortical cells often receive binocular inputs and are usually orientation and direction selective. We use a number of techniques to explore how these transformations come about.

In our electrophysiological studies, we record the activity of many individual neurons simultaneously in both thalamus and cortex. In the cat, we are studying the cortical mechanisms responsible for the selectivity for orientation and direction of motion in simple cells. In the macaque, we concentrate on the first stages of color processing in the cortex. We have found that the wiring of the direct inputs to cortex is extremely precise. Given the visual properties of any single layer 4 cortical neuron, virtually all of the thalamic neurons that would help it perform this function are directly connected to it. In order to study the facilitatory interactions between these multiple inputs to cortical neurons, we are currently using multielectrode arrays to record up to ten neurons in the thalamus along with several of their potential targets.

In related projects we are using optical imaging, a technique for mapping the function of neural populations in vivo. These studies produce maps of the visual cortex that show the clustering of neurons with different receptive field properties. Functional maps allow us to target specific types of neurons (such as color-selective cells in the macaque) for electrophysiological study.