McEwen’s team turned lab lights on and off to create 20-hour days for mice, while a control group was kept on a regular 24 hour schedule. Within six weeks, the disrupted group started to gain weight, despite eating the same diet as controls. They grew obese, and had altered levels of insulin and leptin, two key metabolic hormones. Effects extended to their brains. In the prelimbic prefrontal cortex, a region important to emotional control and cognitive flexibility, neurons shrank and were arranged in less complex ways. The mice had trouble learning to navigate mazes, and were spooked by new environments. The researchers hope their model of disruption will be used for further investigation of circadian disruption.