In a nutshell: When the brain’s visual processing centre is damaged, even older brains can find new ways to transmit their visual signals.

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Human vision relies on signals being transmitted from the retina to a part of the brain called the primary visual cortex (V1).

Damage to V1 – following a stroke, for example – disrupts this process, which leads to blindness. Other parts of the brain that normally communicate with V1, such as the lateral geniculate nucleus (LGN), can deteriorate as a result.

However, some resilient LGN cells survive and create new pathways for visual processing. It’s as if you’d mapped your route to a specific location, only to find that it’s no longer accessible. Instead of giving up, you find a new way to reach a similar destination.

As Maureen Hagan, Marcello Rosa, and Leo Lui from the Brain Function CoE explain in a review of research into this area, marmoset monkeys are ideal candidates for studying how the brain adapts to V1 damage because they share key features of the human visual system.

The Brain Function CoE’s Nafiseh Atapour and colleagues studied young adult and very old marmosets to see if their age affects how much of the LGN is lost after V1 damage. Although older marmosets (which were equivalent in age to 80–100-year-old humans) lost a larger proportion of their LGN cells, some cells still survived and could transmit visual signals.

Their research shows that even in old age, the brain is remarkably flexible in response to injury. This knowledge may help to restore some vision to people who have lost it due to stroke.

Next steps:
The team plans to study LGN cells more closely to see if the cells that survive after V1 damage have any common features. They also want to find the brain areas that LGN cells connect to when V1 is no longer working normally.

Atapour, N., Worthy, K.H., Lui, L.L., Yu, H.H., & Rosa, M.G. (2017). Neuronal degeneration in the dorsal lateral geniculate nucleus following lesions of primary visual cortex: comparison of young adult and geriatric marmoset monkeys. Brain Structure and Function, doi: 10.1007/s00429-017-1404-4

Hagan, M.A., Rosa, M.G., & Lui, L.L. (2017). Neural plasticity following lesions of the primate occipital lobe: The marmoset as an animal model for studies of blindsight. Developmental Neurobiology, 77(3), 314-327.

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