Tiny antenna-like organelles once thought to be holdovers from our ancient past appear to play a crucial role in keeping track of time, according to a recent study on mice by researchers from the University of California, Irvine (UCI), in the US. Known as cilia, the microtubule projections can be found throughout the more complex branches of the tree of life, including on many of our own cells. Where they often have a role in motion, either pushing cells around or moving materials close to their surface, most in the human body – described as primary cilia – are non-motile. Initial investigations more than a century ago considered these kinds of structures to be vestigial. Today, many primary cilia are recognized as part of a signaling hub system that keeps the body adapting and responding appropriately. While various roles of primary cilia in receiving and responding to sensory information have been established, little is known about how these organelles fit in with higher-order cognitive functions going on in the brain. Part of the job of the area of the brain known as the striatum is to act as this central clock, coordinating motor movements, learning, planning, and decision-making. It's also important for managing working memory and maintaining attention. For their study, the researchers used a gene manipulation technique to remove striatum cilia in mice, which had a dramatic effect. While the mice could still maintain long-term memories and habitual or already learned motor skills, various negative effects were observed after the cilia removal. The rodents proved unable to learn new motor tasks and showed repetitive motor behavior as well as noticeable delays in making decisions. Their ability to quickly recall location and orientation information, and their ability to filter out irrelevant environmental sensory information, were negatively affected. A variety of tests and exercises were carried out with the mice to make these conclusions, including putting the animals through mazes and testing their ability to recognize objects and locations. "Successful performance of working memory, attention, decision-making and executive function requires accurate and precise timing judgment, usually within a millisecond to a minute," says UCI neuroscientist Amal Alachkar. "When that capacity is impaired, it means losing the ability to quickly adjust behavior in response to changes in external stimuli and failing to sustain appropriate, goal-oriented motor responses." It's clear that all the impacts of cilia removal have a shared characteristic: the loss of ability to quickly change behavior in response to changes in the environment in an appropriate time frame. How the results of this study relate to humans isn't yet fully known, but it's likely that the human brain's cilia work in a similar way to those in mice. The researchers are already working on follow-up studies to analyze the relationship between cilia and time perception more closely. Not only does the finding improve our understanding of how we perceive the world, but could help us to fix it in cases our view of time goes wrong. Impaired time perception and a faulty judgment of time is a characteristic found in numerous mental and neurological disorders, including schizophrenia, Parkinson's disease, Tourette syndrome, autism spectrum disorder, and Huntington's disease. "Our results may open new avenues for effective intervention through cilia-targeted therapies for treatment," says Alachkar. "Our ongoing work is aimed at understanding the mechanisms by which cilia regulate time perception and developing targeted therapies to improve behavioral deficits." Source
