A team of neuroscientists have advanced their understanding of how neurons adjust the speed of information flowing through an axon to compensate for its branched design. Axons, with their long, spindly arms utilize a generous amount of cell tissue. Also, recent studies have shown that axons put the break on signal flow speed and do not transmit signals as quickly as they could. This new study, published in Scientific Reports, proposes that neurons actively make adjustments in signal processing in order to maintain operating efficiency as measured by the refraction ratio.
The neuron refraction ratio is defined by the refractory period over the latency period. The refractory period is the time between sending signals and signal latency is the time it takes for information to travel down an axon. The study looked at the refraction ratio of axonal branches of nearly 12,000 rat Basket cell neurons and found the median value to be 0.92, which is close 1.0, the ratio that is theoretically predicted to be a perfect balance. Researchers used 3D morphological data to reconstruct models of axonal branches and compared calculations of signal delay to refraction period to determine refraction ratio.
The study shows that no matter the axon shape—straight or curvy, long or short—their refraction ratio always approached one. This finding suggests that axons grow in a way to slow down signal transmission in order to optimize the refraction ratio. There can be a breakdown in the flow of information when neurons don’t optimize signal transmission, as could be the case in autism spectrum disorder.
"The hypothesis we have is that the refraction ratio deviates from the ideal in neurodevelopmental disorders such as autism," says Gabriel Silva, head of the lab where the study was conducted. "We think that may be the case for individual neurons, as well as networks of neurons."
The research team believes this new understanding of how neurons optimize signal processing will enable studies to investigate ow information flow is interrupted in schizophrenia and other neurological disorders. In addition, it could improve our understanding how different drugs impact synaptic transmission between neurons.
Image: Illustration of a neuron. Image courtesy of David Baillot/ UC San Diego.