As many as one-third of people who survive a stroke lose their eyesight – and most will not fully recover their vision. Known as ‘cortical blindness’, their loss of vision is the result of damage to the primary visual cortex (V1), which blocks the flow of information from the eyes to the brain. This damage also triggers degeneration in brain regions that send visual information to V1, such as the lateral geniculate nucleus (LGN). However, some LGN cells can survive and retain their visual function.
The potential for recovery from cortical blindness was thought to depend on a balance between degeneration and cell survival. But new research from the Brain Function CoE has found a third, previously unknown factor: changes in the chemical activity in LGN cells after V1 damage. The research was carried out by a team led by Marcello Rosa from Monash University.
Normally, LGN cells that send visual information to the cortex use excitatory neurotransmitters – chemicals that help to transmit signals from one cell to the next. Other LGN cells use inhibitory neurotransmitters, which stop signals from going further. This balance of neurotransmitters helps the brain to prioritise which visual information it processes. But after V1 damage, there is a seven-fold increase in the number of LGN cells producing an inhibitory neurotransmitter called GABA. This includes cells that are expected to make the surviving connections to the cortex.
The researchers aren’t sure why cells that need to transmit information produce a chemical that stops transmission. Perhaps it has a positive effect, somehow helping the surviving cells to make the most of their remaining resources. Or it might have a negative effect, limiting the potential for recovery. Either way, this discovery provides neuroscience researchers with new information for understanding – and maybe eventually treating – cortical blindness.
The researchers are investigating the connections made by the surviving cells to see which brain areas they send information to.
Atapour, N., Worthy, K. H., Rosa, M. G. P. (2021). Neurochemical changes in the primate lateral geniculate nucleus following lesions of striate cortex in infancy and adulthood: implications for residual vision and blindsight. Brain Structure and Function, https://doi.org/10.1007/s00429-021-02257-0