Most people feel groggy after hopping time zones. This is the body’s response to the temporary mismatch between the new local time and the body’s natural 24-hour circadian rhythm. This rhythm in mammals is governed by the suprachiasmatic nucleus (SCN) on a hormonal and neuronal level. The SCN is a small region in the brain that is located above the two optic (eye) nerves. However, long flights are not the only things that are responsible for this mismatched chaos. As we get older, the SCN makes a weaker circadian rhythm, which often results in sleep conditions, depression, and metabolic syndrome.
Medical literature has shown a lot of evidence for the age-related weakening of the rhythm; however, the mechanisms behind it and the connection between the neurons has always remained a mystery. Researchers out of the University of Shanghai for Science and Technology in China have done an experimental analyses of the connections in the SCN in order to better understand the hormonal and neuronal mechanisms of the circadian rhythm. This will hopefully help in the development of potential treatments for what we commonly call jet lag, as well as other sleep disorders. The goal of the experiment was to determine the degree of heterogeneity, or the measure of the number of “hub” nodes in a network that connect to other nodes.
Generally, networks have links and nodes. If there is high network heterogeneity, the hubs link to a number of other nodes. If there is low network heterogeneity, then the topology is flat, and the difference between other nodes and the hubs is limited.
The master clock that is the SCN has about 20,000 neurons that are connected together by neurotransmitters. This network consists of subgroups, with about 25% of coupled neurons receiving light from the retina. The other 75% are then coupled to those neurons (the subgroups are named ventrolateral and dorsomedial).
In their research report, appearing in CHAOS from AIP Publishing, they map out the SCN connections in four different networks, with levels ranging from low to high heterogeneity. The networks were Newman-Watts, all-to-all, Barabási-Albert scale-free, and the Erdös-Rényi networks.
In the all-to-all network, the researchers found that not only was it the least heterogeneous, but the SCN lost the circadian rhythm that was induced by the other networks. This makes the all-to-all network the least likely network type. The amplitude or wave-like crest of the rhythm was biggest in the Barabási-Albert scale-free network.
Changgui Gu, one of the researchers and authors of the study, stated that this experiment suggests that the SCN is heterogeneous, but the details of the network’s structure have not yet been discovered. Gu and colleagues believe that if the network structure in the SCN were heterogeneous, then this would make the circadian rhythm stronger through a small, smooth change in the boundary value of a system, causing a qualitative change in the pattern of arrangement within the network (bifurcation theory).
Researchers state that further research is necessary, but will likely involve collaborative efforts with other researchers around the world to develop medications that will strengthen the SCN heterogeneity in order to counteract the age-related weakening.
Author: Rachael Herman is a professional writer with an extensive background in medical writing, research, and language development. Her hobbies include hiking in the Rockies, cooking, and reading.
© 2020 American Sleep Association.