Summary: The visual cortex continues to develop into our 40s, a new study reports.
Source: McMaster University.
Brain research recasts timeline for visual cortex development.
The visual cortex, the human brain’s vision-processing centre that was previously thought to mature and stabilize in the first few years of life, actually continues to develop until sometime in the late 30s or early 40s, a McMaster neuroscientist and her colleagues have found. Kathryn Murphy, a professor in McMaster’s department of Psychology, Neuroscience and Behaviour, led the study using post-mortem brain-tissue samples from 30 people ranging in age from 20 days to 80 years.
Her analysis of proteins that drive the actions of neurons in the visual cortex at the back of the brain recasts previous understanding of when that 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 Murphy and her colleagues, 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.
“There’s a big gap in our understanding of how our brains function,” says Murphy. “Our idea of sensory areas developing in childhood and then being static is part of the challenge. It’s not correct.”
The research appears May 29 in The Journal of Neuroscience.
Murphy says treatment for conditions such as amblyopia or “lazy eye”, 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.
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, Murphy says.
Funding: Natural Sciences and Engineering Research Council of Canada funded this study.
Source: Kathryn Murphy – McMaster University
Image Source: NeuroscienceNews.com image is in the public domain.
Original Research: Abstract for “Development of glutamatergic proteins in human visual cortex across the lifespan” by Caitlin R. Siu, Simon P. Beshara, David G. Jones and Kathryn M. Murphy in Journal of Neuroscience. Published online May 29 2017 doi:10.1523/JNEUROSCI.2304-16.2017
Development of glutamatergic proteins in human visual cortex across the lifespan
Traditionally, human primary visual cortex (V1) has been thought to mature within the first few years of life, based on anatomical studies of synapse formation, and establishment of intra- and inter-cortical connections. Human vision, however, develops well beyond the first few years. Previously, we found prolonged development of some GABAergic proteins in human V1 (Pinto et al., 2010). Yet as over 80% of synapses in V1 are excitatory, it remains unanswered if the majority of synapses regulating experience-dependent plasticity and receptive field properties develop late like their inhibitory counterparts. To address this question, we used Western blotting of post-mortem tissue from human V1 (12 female, 18 male) covering a range of ages. Then quantified a set of post-synaptic glutamatergic proteins (PSD-95, GluA2, GluN1, GluN2A, GluN2B), calculated indices for functional pairs that are developmentally regulated (GluA2:GluN1; GluN2A:GluN2B), and determined inter-individual variability. We found early loss of GluN1, prolonged development of PSD-95 and GluA2 into late childhood, protracted development of GluN2A until ∼40 years and dramatic loss of GluN2A in aging. The GluA2:GluN1 index switched at ∼1 year but the GluN2A:GluN2B index continued to shift until ∼40 year before changing back to GluN2B in aging. We also identified young childhood as a stage of heightened inter-individual variability. The changes show that human V1 develops gradually through a series of 5 orchestrated stages, making it likely that V1 participates in visual development and plasticity across the lifespan.
Anatomical structure of human V1 appears to mature early, but vision changes across the lifespan. This discrepancy has fostered 2 hypotheses: either other aspects of V1 continue changing, or later changes in visual perception depend on extrastriate areas. Previously, we showed that some GABAergic synaptic proteins change across the lifespan but most synapses in V1 are excitatory leaving unanswered how they change. So we studied expression of glutamatergic proteins in human V1 to determine their development. Here we report prolonged maturation of glutamatergic proteins, with 5 stages that map onto life-long changes in human visual perception. Thus, the apparent discrepancy between development of structure and function may be explained by life-long synaptic changes in human V1.
“Development of glutamatergic proteins in human visual cortex across the lifespan” by Caitlin R. Siu, Simon P. Beshara, David G. Jones and Kathryn M. Murphy in Journal of Neuroscience. Published online May 29 2017 doi:10.1523/JNEUROSCI.2304-16.2017