In a nutshell: A small subpopulation of brain cells in the eye sends alert signals to the brain in response to visual threats.

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When we see something, our eyes send messages to our brain through the optic nerves. Each nerve contains around a million long ‘wires’, called axons, which carry information from ganglion cells in the retina to relevant parts of the brain. Although at least 20 ganglion cell types have been discovered in primate retinas, how each type contributes to visual processing is not clear.

Brain Function CoE investigators Ashleigh Chandra, Sammy Lee and Ulrike Grünert have taken a big step towards identifying which wires are responsible for sending alerting messages to the brain areas that regulate attention. The team used a biological marker to tag all the brain cells in the retina that contain a protein called calretinin. Closer inspection revealed that most of the tagged cells were thorny cells – named after their special thorn-like connections to other cells in the retina.

“We knew that thorny cells project to areas of the brain that help you adjust to new or threatening stimuli in the environment, for example the image of an approaching car when you start to cross the street,” says Chandra. “What surprised us when we counted the thorny cells is that there are a lot more of them than we previously thought.”

This discovery suggests that the eye and brain devote a lot of processing power to threat detection, which may reflect the importance of survival for our ancestors. “Of course, now we have traffic lights to help us avoid threats from cars, but our thorny cells are still there if we need them,” Chandra says.

In addition to revealing an important role for this ganglion cell type, the researchers have confirmed that tagging calretinin is a useful method for studying these cells in the retina.

Next steps:
The team plans to work with other Brain Function CoE researchers to record activity from areas in the brain involved in paying attention, which receive information from the retinal thorny cells.

Chandra, A. J., Lee, S. C. S., & Grünert, U. (2017). Thorny ganglion cells in marmoset retina: Morphological and neurochemical characterization with antibodies against calretinin. Journal of Comparative Neurology, doi: 10.1002/cne.24319.

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