People who smoke pot can feel lost in time—for some, it's part of the draw. Now researchers may have figured out one reason why cannabinoids, the psychoactive compounds in marijuana and hashish, make people feel this way; they disrupt the body's internal clock.
Sleeping, eating, and other activities are all part of a 24-hour physiological cycle known as the circadian rhythm. This internal clock is controlled by neurons in a region of the brain called the suprachiasmatic nucleus (SCN). The SCN normally uses light to reset the clock. That's what happens when you travel from one time zone to another. But absent any sensory input, SCN neurons will still maintain a circadian rhythm: People and animals kept in total darkness continue to eat and sleep at the usual times.
Several years ago, researchers discovered that SCN neurons possess receptors for cannabinoids. In the new study, a team led by Yale University circadian biologist Anthony van den Pol tried to figure out what role these receptors play.
The researchers housed 42 mice in total darkness for 2 weeks to synchronize their internal clocks. In this environment the animals cycled through active and inactive phases lasting about 12 hours each. After 2 weeks, the researchers shined a light into some of the cages shortly after the mice had entered their active phase. Because mice are nocturnal, they became active about 2 hours later in the day than did mice not exposed to light, a phenomenon called "phase delay." But mice given brain injections of cannabinoids before light exposure exhibited much less of a phase delay; they became active only 1 hour later than did animals not exposed to light.
The researchers then looked at the SCN cells themselves. When they added cannabinoids to mouse SCN cells in a petri dish, the cells fired about 50% more frequently. This increased activity likely mucks up the circadian rhythm in a live mouse, the researchers reported  online this week in The Journal of Neuroscience.
The team believes cannabinoids may have a similar effect in humans. People tend to lose track of time when they smoke pot, van den Pol says. That may be because the cannabinoids in the drug cause their SCN neurons to fire erratically, he says, disrupting their internal clock.
Joseph Bass, a circadian researcher at Northwestern University in Evanston, Illinois, says the work supports the idea that addictive substances can impact the body's circadian rhythm. Anecdotally, this may seem obvious, but until recently studies of addictive substances focused only on the brain's reward system. Evidence that molecules can impact both the reward system and the circadian system is just emerging, Bass says.