How the brain gets wired for stereo vision

Nerve cells that transmit light signals from the eye into the brain use a molecule best known for its role in blood vessel growth as a 'stepping stone' to help them reach the opposite brain hemisphere, according to research published in Neuron. When light enters our eye, it passes through to the retina in the back of the eye, where it is converted to electrical signals that pass along nerve cells known as retinal ganglion cells. These ganglion cells follow a path into the brain, where they reach an area known as the optic chiasm. At this point, the path forks and the signal passes to both hemispheres of the brain - this is essential in order to create stereo vision, which allows us to see perspective. However, until now, it has not been clear what guides the nerves to cross to the opposite side of the brain at the chiasm - why, for example, doesn't light from the right eye just pass to the right side of the brain rather than reaching to the left hemisphere? The answer, according to Dr Lynda Erskine from the University of Aberdeen and Dr Christiana Ruhrberg, a Wellcome Trust New Investigator (UCL Institute of Ophthalmology)is that a molecule known as VEGF164, which ordinarily plays a part in the growth of blood vessels, acts as a stepping stone, allowing nerve cells carrying images from each eye to cross the chiasm and reach the opposite hemisphere. The researchers developed a mouse model that allowed them to track how the ganglion cells are wired during fetal development. In mice lacking VEGF164, the axons of many retinal ganglion cell neurons do not cross to the opposite hemisphere.