Distinguished Speaker Series | Carol Mason, PhD

The developing visual system could easily turn into a traffic pileup. Nerve cells, or neurons, extend roots from the retina, in the back of the eye, several centimeters into the brain. And somehow they seem to know precisely where they are going. At Columbia’s Mortimer B. Zuckerman Mind Brain Behavior Institute, Carol Mason, PhD, studies the circuitry of the visual system to understand how neurons that extend from the eyes make their way to their specified destinations deep in the brain.

She studies a type of neuron called the retinal ganglion cell (RGC) that stretches from the back of the eye to the thalamus and midbrain, which are sensory relay stations in the middle of the brain. (From these sites, signals are sent to the visual stations in the cortex, the brain region that interprets these signals.) Projecting from one end of each neuron is a thick root called an axon. About half of the RGCs send their axons to the part of the thalamus that sits on the same side of the brain in which they are located, while the axons from the other half of the RGCs cross over to the opposite side. This splitting of the circuit—by which each side of the brain receives signals from both eyes—allows for binocular vision. The question is, how does an axon, once it reaches the intersection at the brain’s midline (called the optic chiasm), know whether to cross over or remain on the same side?