A new finding challenges conventional wisdom about the mind’s internal clock
Researchers have found some misbehaving neurons in the part of the brain that tells time. The startling discovery could change how neuroscientists think about the brain’s influence on the body’s biological rhythms, and has raised questions about the very definition of a functioning neuron.
At the University of Manchester in England, electrophysiologist Mino Belle studies the electrical activity of neurons in the mammalian suprachiasmatic nucleus, or SCN. Although no bigger than a grain of rice, the SCN is the brain’s central timekeeper and command center in charge of coordinating the cycles, called circadian rhythms, that determine the crucial timing of processes like hormone release, the sleep-wake cycle, and metabolism.
Neuroscientists like Belle are busy trying to figure out how and why the cells in the SCN behave the way they do, because insights at the cellular level could lead to more effective therapies for sleep disorders, like insomnia and narcolepsy, as well as disorders linked to disrupted circadian rhythms, like shift work sleep disorder and jet lag. Understanding what makes the SCN tick could also lead to better therapies for metabolism disorders like diabetes.
For decades, conventional wisdom has said that SCN neurons fire frequently during the day, while an individual is awake, and rest at night. But researchers now know that not all SCN neurons are created equal. Specifically, not all of them contain genes that code for a specific type of “molecular clock.”
In 2007, Belle began experimenting with mice that were genetically engineered so their clock-containing SCN cells would glow fluorescent green, standing out amongst their neighbors. When he recorded only from clock-containing cells, he observed a perplexing pattern in the data: instead of firing during the day, these cells were actually at rest.
Even stranger: they were resting in an electrical state never before recorded in healthy neurons.
“When we started to see the behavior, it took me several months to accept,” said Belle. “But it was overwhelmingly the case.” Belle spent those months not only replicating the result, but also performing various tests to make sure the cells were healthy. His findings were published in the October 9 issue of the journal Science.