Some people with anxiety and depression may just have internal clocks that aren’t ticking right, and giving them a tuneup could help treat the mental illnesses.

Findings published in the journal Biological Psychiatry suggest that disruptions in the circadian rhythm, the body’s timekeeping system that tells us when to sleep and eat and keeps our organs moving to the same choreography, are enough on their own to cause the conditions. While such disruptions have previously been associated with mood disorders like depression and bipolar disorder, there was a question of the chicken or the egg — it was unclear whether the illnesses caused the disturbances or vice versa.

Researchers from the University of California at San Diego studying mice found that the latter was true: When they manipulated mouse genes to suppress the ones in the brain responsible for regulating their circadian rhythm, the study says, the mice “were slower to escape” from an uncomfortable situation, which is a sign of hopelessness, and gained more weight than control mice despite eating the same portions. Those affected mice additionally spent less time in bright light, considered to be a sign of anxiety, and “they also spent more time immobile” when suspended by their tails.

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“Our data show that perturbing circadian rhythms in otherwise totally undisturbed animals is enough to cause behaviors similar to human depression,” first author Dominic Landgraf of UC San Diego said in a statement.

Our internal clock has long been believed to be linked to mental health, and experts recognize conditions that are closely tied to the rhythm of day and night. Seasonal affective disorder, for example, is a form of depression that follows the cycle of the seasons, with reduced daylight in winter being one of its drivers. Our circadian rhythm is an internal regulation, but it can be influenced by environmental factors.

“It is perhaps not surprising that disruptions of our natural synchronization can have heavy impacts on our physical and mental health,” Landgraf said.

He suggested that targeting the circadian rhythm could one day prove a new way to treat depression.

Read: How Therapy Can Treat Seasonal Affective Disorder, The Winter Blues

Source: Welsh DK, Landgraf D, Long JE, Proulx CD, Barandas R and Malinow R. Genetic Disruption of Circadian Rhythms in the Suprachiasmatic Nucleus Causes Helplessness, Behavioral Despair, and Anxiety-like Behavior in Mice. Biological Psychiatry. 2016.