"'What we found in this study was that as people get older, they tend to have a loss of rhythmicity in a number of these core clock genes,' she says. It's likely throwing their timing out of whack. That finding was expected."

"But they also found something else: another set of genes that seemed to pick up a rhythm, but only in older brains. That second set of genes, McClung speculates, might be working like a backup clock that starts ticking when the main one becomes less reliable."

"If that's the case, it could be contributing to neurodegenerative and psychiatric diseases that tend to set in later in life, many of which involve changes in the sleep-wake cycle."

"'We're particularly interested in a condition called sundowning, where people become agitated and irritable and anxious only in the evening, and this is usually in older people that have dementia,' McClung says. Their backup clock genes might not be kicking in correctly, she says."