Neuroscientists know that some connections in the brain for processing visuals are pruned through neural development. This knowledge may, however, be wrong, scientists from Virginia Institute of Technology have discovered.
Retinal neurons associated with vision generate connections in the brain -- and as the brain develops, it strengthens and maintains some of those connections more than others.
The disused connections are eliminated.
"We found that this activity-dependent pruning might not be as simple as we would like to believe," said Michael Fox, associate professor at Virginia Tech's Carilion Research Institute.
Fox and his team of researchers used two different techniques to examine how retinal ganglion cells -- neurons that live in the retina and transmit visual information to the visual centres in the brain -- develop in a mouse model.
Using a technique dubbed "brainbow", the scientists tagged the terminals with proteins that fluoresce different colours.
The researchers thought one colour, representing the single source of the many terminals, would dominate in the clusters.
Instead, several different colours appeared together, intertwined but distinct.
The samples showed a true "brainbow".
"I could see, right in front of me, something very different than the concept I learned from my textbooks," added Aboozar Monavarfeshani, graduate student in Fox's laboratory who tagged the terminals.
The results showed individual terminals from more than one retinal ganglion cell in a mature mouse brain.
The study is a direct contradiction to some other research indicating that neural development weeds out most connections between retinal ganglion axons and target cells in the brain.
"The research provides strong evidence for multiple innervation and calls for a reevaluation of the current understanding of information flow and neural circuit maturation in the visual system," noted Albert Pan, assistant professor in the Medical College of Georgia at Georgia Regents University.
"The lesson in this particular study is that no single technique gives us all the right answers. Science is never as simple as we like to make it seem," Fox concluded.
The results were published in the journal Cell Reports.
