May 10, 2012

VU research team’s vision study yields eye-opening results

Vivien Casagrande, PhD

VU research team’s vision study yields eye-opening results

The pulvinar, a mysterious structure buried in the center of our brains, determines how we see the world — and whether we see at all.

That’s the dogma-shattering conclusion reached by Vanderbilt University neuroscientists in a report published online this week in the journal Nature Neuroscience.

Vivien Casagrande, Ph.D.

Vivien Casagrande, Ph.D.

The pulvinar sits at the back of the thalamus, a walnut-sized structure that relays sensory and motor signals to the cerebral cortex, the outer, “thinking” part of our brains, and which also regulates sleep and alertness.

The classical view of vision is that signals from the retina are sent to a tiny relay station in the thalamus called the lateral geniculate nucleus. It, in turn, sends the information on to the primary visual cortex at the back of the brain.

But when the Vanderbilt researchers inactivated the pulvinar, they discovered something extraordinary — the primary visual cortex stopped responding to visual stimulation. The pulvinar, in essence, is a switch so powerful that when it is turned off, it can overrule the visual input and prevent the brain from seeing.

This result “was stunning and suggests that we don’t really understand how this system works, that we need to revise the way we look at how the thalamus operates,” said senior author Vivien Casagrande, Ph.D., professor of Cell & Developmental Biology, Ophthalmology & Visual Sciences and Psychology.

Schizophrenia, attention deficit hyperactivity disorder (ADHD) and “mad cow disease” all are associated with damage to the pulvinar, which is suspected to regulate visual attention among many other yet-to-be defined functions.

“Our finding offers hope for better understanding of the neural circuits underlying the symptoms of these diseases,” she said.

Casagrande is known internationally for her contributions to evolutionary, developmental and sensory systems neuroscience. Her co-authors on this paper were postdoctoral research fellow Gopathy Purushothaman, Ph.D., the first author, and graduate students Roan Marion and Keji Li.

The study was supported by the National Institutes of Health.