Science & Research

Scientist shines light on how vision affects sleep cycle

The Harvard professor discussed how to help regulate the circadian rhythms of blind people

Contributing Writer
Wednesday, November 20, 2013

When the sun set in the middle of Harvard Associate Professor of Medicine Steven Lockley’s lecture, Lockley’s  computer darkened as a program called f.lux automatically disabled his computer’s blue light. Blue light has been shown to stimulate cognitive brain activity even in visually blind individuals and should be eliminated before bed to facilitate sleep, Lockley said.

A group of 15 experts gathered Tuesday night to hear Lockley talk about advances in how scientists understand “the relative contributions and interactions of visual and non-visual photoreceptors in mediating the physiological effects of light, and the role of light wavelength, timing, duration,” in a seminar organized by the Providence Sleep Research Interest Group, according to an email from Professor of Psychiatry and Human Behavior Mary Carskadon.

Humans have an internal clock — called a circadian rhythm — that measures light levels from the sun and programs important bodily functions, such as waking up from a night’s sleep.

“We need a daily, light-dark cycle to reset our clock,” Lockley said. “Many people think still that (blind people) have no rhythms.”

In reality, the clock works but fails to synchronize to a 24-hour rhythm. In studies of totally blind individuals, 100 percent of test subjects experience non-24-hour cycles, according to Lockley’s slides. But researchers may be on the verge of a solution.

A team at Vanda Pharmaceuticals has presented the Food and Drug Administration with two successful clinical trials in which Tasimelteon, a melatonin receptor agonist, was used to correct the non-24-hour cycle.

“As a field, we need to start pushing hard the need for circadian phase assessments to diagnose circadian disorder,” Lockley said. He chastened the International Classification of Sleep Disorders for suggesting physicians take only seven days to diagnose a non-24-hour sleep-wake disorder, when it generally takes about a month to ascertain a diagnosis.

“You completely change your mind when you get more data,” Lockley said. “With one month it is still not always possible to see if someone has a circadian disorder.”

Lockley also shined light on how phase angle, a measurement of how an individual’s sleep cycle is shifted from the 24-hour normal, can affect mood and performance. “Phase angle is what really drives these daytime symptoms and daytime function.”

A normally entrained individual wakes four hours after a neurological peak in the concentration of sulfate.  People whose cycles are “advanced do go to sleep earlier and wake earlier in clock time, but wake later in their circadian phase,” Lockley said.  “Advanced type are better in the morning, but fall off more rapidly because they wake at equivalent of noon.”

The “delayed” go to bed later and wake up later in clock time, but since they arise early in their circadian phase, their performance and mood tend to be significantly impaired.

Lockley also tackled what he called a prevalent misconception among his peers that significant exposure to light is necessary to have a biological effect.

“I don’t understand why. We all know it does,” Lockley said. Even the small amount of light visible “in the evening is pushing the teenagers (further),” keeping them up late into the night, Lockley said.

Lockley is doing “incredibly important work at a really basic level. Bringing it into the applied realm is really important,” Carskadon said, citing the possiblity of manipulating the human response to light-dark cycles to help people stay awake and sleep soundly.

Lockley suggested in his lecture that “lighting design optimize visual and non-visual effects,” as with the f.lux program on his computer.

Looking at the number of practical applications already surfacing as a result of this research, it’s clear “there’s still a lot of work to be done in this area,” said Instructor in Psychiatry  and Human Behavior Eliza Van Reen, who did postdoctoral work in Lockley’s lab.