The research is complex but here is the simplified version.
The consensus is that the primary visual cortex stops developing at around the age of 5 or 6 years. Development of the visual cortex is linked with different inhibitory (GABA) and excitatory (glutamate) neurotransmitters. The right balance can either enhance or inhibit brain plasticity.
In this study, the team analyzed postmortem brain tissue of 30 people, ranging in age from 20 days to 80 years. They found that some of the “glutamatergic proteins develop until late childhood, but others develop until around the age of 35-40”.
Who might this be important for?
Treating adult amblyopia has been considered futile, as their visual cortex is thought to not respond to treatment anymore. However, this research suggests that certain brain areas still have plasticity and are more flexible than previously thought. (via)