The neurons in the SCN are coupled oscillators, like these metronomes on a moveable table that has enough wiggle that each metronome’s motion affects the others’. Like the metronomes the neurons keep time individually and, because the VIP network couples them, they synchronize their beats.
Video by the Ikeguchi Laboratory, in the graduate school of science and engineering at Saitama University in Japan.
Did you know you have a biological clock in your brain that drives your sleep patterns and metabolism?
The clock is mostly in a brain region called the suprachiasmatic nucleus—a collection of about 20,000 brain cells, or neurons. Each one of these neurons can keep time, just like a metronome sitting on a piano. Together, these 20,000 biological clocks are kept perfectly synchronized, and they are accurate to about a few minutes within a 1440-minute day. A brain signaling chemical called VIP (vasoactive intestinal polypeptide) plays an important role in keeping all of the neurons ticking in unrelenting lock step. But VIP doesn’t work alone.
An NIH-funded team, led by researchers at Washington University in St. Louis, has discovered that another brain signaling molecule, called GABA (gamma-amino-butyric acid), helps these clocks stay in synch. But GABA also gives these neurons a little wiggle room so they can respond to environmental cues. Although this network of clock neurons allows for gradual changes in seasonal day length, it can’t respond well to large shifts that weren’t often encountered in evolution—such as crossing time zones or working night shifts. This may explain why such time changes wreak havoc on our body.
VIP seems to decline with age. Without this synchronizing molecular taskmaster, clock neurons are influenced by the more lenient GABA—which allows them to tick to their own beat. Perhaps that’s why, as we age, our sleep/wake cycle becomes more erratic and fragmented.
GABA Networks Destabilize Genetic Oscillations in the Circadian Pacemaker. Freeman GM Jr, Krock RM, Aton SJ, Thaben P, Herzog ED. Neuron. 2013 Jun 5;78(5):799-806.
If you want to know how this worked, check out Robert Krulwich’s explanation on NPR’s Blog post.
NIH support: National Institute of Mental Health; National Institute of Neurological Disorders and Stroke