To further study human vision, lead author Kathryn Murphy, a professor in the Department of Psychology, Neuroscience and Behavior at McMaster University, and co-authors obtained post-mortem brain-tissue samples from 30 people ranging in age from 20 days to 80 years to study how expression of a set of glutamatergic proteins (PSD-95, GluA2, GluN1, GluN2A, GluN2B) — which regulate neurotransmission at a majority of synapses in the human visual cortex — changes in this region over time.
Their analysis recasts previous understanding of when this part of the brain reaches maturity, extending the timeline until about age 36, plus or minus 4.5 years.
The finding was a surprise to the authors, who had expected to find that the cortex reached its mature stage by 5 to 6 years, consistent with previous results from animal samples and with prevailing scientific and medical belief.
“Our results show development of the visual cortex occurs in five different stages that mirror changes in vision,” the researchers said.
For example, the expression of three of these proteins — GluN1, PSD-95 and GluA2 — peaks between 5 and 11 years of age, which coincides with the end of the period when children are susceptible to developing amblyopia, or lazy eye.
Another protein, GluN2A, did not peak until about 40 years of age and then dropped dramatically, by about 75%, in adults over 55 years of age, perhaps signaling degeneration in the visual cortex.
“There’s a big gap in our understanding of how our brains function,” Prof. Murphy said.
“Our idea of sensory areas developing in childhood and then being static is part of the challenge. It’s not correct.”
“Treatment for conditions such as amblyopia, for example, have been based on the idea that only children could benefit from corrective therapies, since it was thought that treating young adults would be pointless because they had passed the age when their brains could respond,” Prof. Murphy added.
“Though the research is isolated to the visual cortex, it suggests that other areas of the brain may also be much more plastic for much longer than previously thought.”
This research was presented in a paper published in the Journal of Neuroscience on May 29, 2017