He led an experiment in which mice were forced to live on a 20-hour cycle, rather than the usual 24-hour cycle. Although the animals got the same number of hours of sleep, it was of a different, less restorative quality. Just as occurred among humans who slept too little, immune system function suffered. Some mice had sluggish immune responses to an intentionally administered immunity challenge, while others showed overactive responses."This represents a very clear dysregulation of the system," said Karatsoreos. "The system is not responding in the optimal manner.”