The suprachiasmatic nucleus functions beyond circadian rhythm generation

Abstract

We recently discovered that human activity possesses a complex temporal organization characterized by scale-invariant/self-similar fluctuations from seconds to ~4 hour-statistical properties of fluctuations remain the same at different time scales. Here, we show that scale-invariant activity patterns are essentially identical in humans and rats, and exist for up to ~24 hour: six-times longer than previously documented. Theoretically, such scale-invariant patterns can be produced by a neural network of interacting control nodes-system components with feedback loops-operating at different time scales. However such control nodes have not yet been identified in any neurophysiological model of scale invariance/self-similarity in mammals. Here we demonstrate that the endogenous circadian pacemaker (suprachiasmastic nucleus; SCN), known to modulate locomotor activity with a periodicity of ~24 hour, also acts as a major neural control node responsible for the generation of scale-invariant locomotor patterns over a broad range of time scales from minutes to at least 24 hour (rather than solely at ~24 hour). Remarkably, we found that SCN lesion in rats completely abolished the scale-invariant locomotor pattern between 4 and 24 hour and significantly altered the patterns at time scales <4 hour. Identification of the control nodes of a neural network responsible for scale invariance is the critical first step in understanding the neurophysiological origin of scale invariance/self-similarity. KeywordsActivity; Scale-invariance; Suprachiasmatic nucleus lesion; Human; Rat; Network The suprachiasmastic nucleus (SCN) in mammals generates self-sustained oscillations that orchestrate a wide range of neurophysiologic functions-from cellular processes to overt behaviors-with a time period of ~24 hour (Weaver, 1998). One of the fundamental processes influenced by the SCN is motor activity, which displays clear ~24 hour rhythms even under

The Circadian System in Alzheimer’s Disease: Disturbances, Mechanisms, and Opportunities

“…This is of interest, because scale invariance in activity patterns is found in rodents to be dependent on the SCN (33), and so the changes observed in AD might be taken as indicative of changes occurring in the master clock that are then translated into gross patterns of behavior. This finding is in accordance with the findings from neuropathological studies discussed later.…”

Simulated shift work in rats perturbs multiscale regulation of locomotor activity

“…Specifically, decreased a (less than 1) in activity fluctuations at large timescales has been observed in animals after the lesion of the SCN (more than approx. 4 h) [7] and in humans with aging and in dementia (more than approx. 2 h) [11].…”

“…This is consistent with our previous study in which we showed that the SCN itself cannot generate scale-invariant patterns [24] despite the fact that the ). The dashed curve is the fitting line derived from SCN-lesion animals [7]. On the abscissa, n represents the timescale in hours.…”

Slow waves during sleep in crayfish. Origin and spread

“…However, there are examples of neuronal spontaneous electrical oscillations whose function is known, such as neurons from the isolated suprachiasmatic nucleus, which become coupled to perform two main functions, i.e. timekeeping and controlling the circadian overt rhythm (Colwell, 2000;Silver and Schwartz, 2005;Hu et al, 2007;Bernard et al, 2007).…”