Neurobiology

Richard T. Born, M.D.

Professor of Neurobiology

Born Website: http://www.hms.harvard.edu/bss/neuro/bornlab/

My lab is interested in the neural circuitry of the primate visual cortex and how it relates to perception and visually guided behavior. Our current focus is on areas of the brain that make calculations about out visual motion. In what direction is it moving? How fast? Is it really moving with respect to its surroundings, or does it just seem to be moving because IÍm moving? The calculations that allow an animal to answer these critical questions are performed by single neurons which are anatomically arranged to form a map representing all possible directions of motion in all parts of the visual field. Superimposed on this map is a coarser organization of neurons whose receptive fields have differing center-surround interactions with respect to moving stimuli. This organization consists of slab-like clusters of cells whose receptive fields have motion opponent surrounds (local-contrast motion columns) interdigitated with clusters of cells whose receptive fields have additive surrounds (wide-field motion columns). We believe that these neurons are performing calculations necessary for distinguishing object-related motion from self-motion. This sensory mapping appears to be crucial for ensuring that the right information is made available to motor systems that must do intelligent things in the world if the animal is to survive.

We use combinations of extracellular electrophysiology, 2-deoxyglucose mapping and anatomical tracing techniques in order to learn the nature of the neural circuitry and the sorts of calculations that it makes. This allows us to make predictions about what that circuit is doing for the animal-predictions which we can test by manipulating the circuits electrically to assess their role in behavior. If we have formulated our theories correctly, we should be able to perturb the behavior in specific and interesting ways.

Correlation of 2-deoxyglucose (2dg) labeling and neuronal receptive field properties in the middle temporal visual area (MT). The gray-level image at the top center is an autoradiograph of a section through MT cut parallel to the cortical surface. The patterns of 2dg uptake were produced by showing the animal a wide-field pattern of random dots (covering ~60 degrees of the visual field) that moved coherently at systematically varied directions and speeds while 2dg was infused intravenously. Regions of high 2dg uptake appear dark (wide-field motion columns), while regions of 2dg uptake equal to that of unstimulated cortex are lighter (local-contrast motion columns). The graphs immediately below the 2dg image depict the responses of two representative neurons to patches of random dots moving in the cellÍs preferred direction and speed as a function of the size of the random dot patch (area response test). Neurons in the dark regions respond more vigorously as the area of the random dot patch increases; neurons in the light regions respond well to small patches of motion but are indifferent to wide-field motion due to the presence of opponent surrounds.