Plastic and Fantastic

Figure 1. The retina-pulvinar-MT pathway supports the preservation of vision following a lesion of the primary visual cortex (V1) in early life (1). LGN, lateral geniculate nucleus, MT, middle temporal region of the cortex.

A recent study (1) has shed new light on how the brain can reroute visual information to bypass damaged areas and preserve vision. As vision is the most complex of our senses, over half of the cerebral cortex is devoted to facilitating it. Typically, signals travel from the retina via the lateral geniculate nucleus (LGN) in the thalamus and on to the primary visual cortex (V1). From there, it is distributed to other areas of the visual cortex. The middle temporal (MT) area of the visual cortex also receives input from the LGN. If this pathway is damaged, it can often result in cortical blindness. However, children with lesions in the V1 area can often retain vision, while adults with identical injuries go blind.

The study involved removing sections of V1 in neonatal and adult marmoset monkeys, then using neural tract tracing, diffusion magnetic resonance imaging and immunohistochemistry to measure brain and visual activity. In the neonatal monkeys, damage or removal of V1 resulted in greater connectivity between the retina and the pulvinar nucleus of the thalamus, and degeneration of retinal input to the LGN, when compared with both controls and adults with V1 lesions – indicating the potential importance of the pulvinar in preserving vision. To date, research has mainly focused on the role of the retina–LGN–MT pathway in the absence of the primary visual cortex, but the study authors argue that the retina–pulvinar–MT pathway, and its ability to restructure itself in childhood, has not been accounted for. “Decades of research have focused on one pathway in the brain thought to be responsible for conscious vision. We knew the brain has the capacity to rewire itself following injury or trauma but the idea that there is a second pathway providing visual information to the brain is a relatively new phenomenon,” said James Bourne, a professor at Monash University, Australia, who led the study. “Our research proves a second pathway exists (Figure 1), but significantly it also shows the brain is much more plastic than originally believed.”

“The next step is to undertake more work to better understand the complex circuitry of the visual brain and how pathways are established in early life and removed at a later stage,” added co-author Claire Warner, stating “We’re a long way off but this opens up a whole new line of inquiry to see if we can develop regenerative techniques to restore vision loss.”