Clock News

Three interesting press releases/news-reports today. Click on links to read the whole articles:

Daytime light exposure dynamically enhances brain responses:

Exposure to light is known to enhance both alertness and performance in humans, but little is understood regarding the neurological basis for these effects, especially those associated with daytime light exposure. Now, by exposing subjects to light and imaging their brains while they subsequently perform a cognitive test, researchers have begun to identify brain regions involved in the effects on brain function of daytime light exposure. The findings are reported by Gilles Vandewalle and Pierre Maquet of the University of Li ge, Derk-Jan Dijk of the University of Surrey, and additional colleagues and appear in the August 22nd issue of the journal Current Biology, published by Cell Press.

Our brain does not use light only to form images of the world. Ambient light levels are detected by our nervous system and, without forming any image, profoundly influence our brain function and various aspects of our physiology, including circadian rhythms, hormone release, and heart rate. These responses are induced by a special non-image-forming (NIF) brain system, which researchers have begun to characterize in animal models. In human studies, much work has focused on the effects of nighttime light exposure, but little is known about daytime responses to light. Especially mysterious are the neural correlates of these responses, and their temporal dynamics. Such issues are of significant interest given that daytime sleepiness is a major source of complaint in modern society and has considerable socio-economic implications.

In the present study, the researchers showed that a brief (21-minute) morning exposure to a bright white light increases alertness and significantly boosts the brain's responses to an experimental test that requires attention only to sound. In a parallel neuroimaging analysis, this boost in alertness was found to correlate with responses in various areas of the brain, including regions of the cortex known to support performance on the auditory test. The regional brain changes were found to be highly dynamic, dissipating within a few minutes. These new findings therefore show that light exposure, even during the day, can quickly modulate regional brain function in areas involved in alertness and non-visual cognitive processes.

UM scientist sheds light on workings of internal clock:

Meredith specifically studied gates known as BK channels that control large flows of potassium out of the cell. Prior research suggested that BK channels were controlled by the core clock, so it made sense to Meredith that the channels might play some role in the generation of circadian behaviors.

To make the connection, Meredith, a self-described scientific jack-of-all-trades, brought a mixed bag of new scientific tools and techniques to an old problem.

The first step required her to combine genetic engineering with behavioral science. She engineered mice that had no functioning BK channels in their clock neurons, then watched how they acted. When exposed to light, the engineered mice behaved just like those with BK channels: They ran on their wheels at night and slept during the day. But when the engineered mice were kept in the dark they went haywire.

"We saw a very dramatic difference," Meredith said.

Their strict schedule loosened and they roamed their cages and ran on their wheels at erratic times. Their daily amount of activity stayed about the same, but it was spread out more evenly over the 24-hour period.

Their strict schedule loosened and they roamed their cages and ran on their wheels at erratic times. Their daily amount of activity stayed about the same, but it was spread out more evenly over the 24-hour period.

Meredith had, for the first time, established a link between specific circadian behaviors in the mice and an ion channel on clock neurons.

But the jump from cellular structure to behaviors was a large one. She still needed to find out how her engineering had affected the intermediate step in the process: the electrical signaling in the brain. This phase of the study required her to switch gears and study the electrical properties of nerve cells.

She found that the clock neurons in her engineered mice generated signals different from those in normal mice. Moreover, the odd patterns of signaling corresponded to the odd patterns of behavior in the mice.

Meredith and her colleagues at Stanford had connected the dots between the BK channel and mice behavior patterns. In the engineered mice, the core genetic clocks seemed to be working fine, but the clock appeared to be unable to communicate well with the parts of the brains where actions such as wheel running were generated.

"The signal for time is no longer being transmitted to the legs," Meredith said. "It's like you have an actual clock and you put a piece of tape over it so you can't see the dial anymore."

The results of her study were published in June in the journal Nature Neuroscience. Her work appears to be the first to link a specific cellular structure in the clock neurons to specific circadian behaviors patterns they generate, said Roberto Refinetti, a psychologist at the University of South Carolina and editor of the Journal of Circadian Rhythms.

"The clock itself has been much-studied," Refinetti said. "The novelty of this is being on the output side."

Constant Lighting May Disrupt Development of Preemie's Biological Clocks:

Every year about 14 million low-weight babies are born worldwide and are exposed to artificial lighting in hospitals.

"Today, we realize that lighting is very important in nursing facilities, but our understanding of light's effects on patients and staff is still very rudimentary," said William F. Walsh, chief of nurseries at Vanderbilt's Monroe Carrel Jr. Children's Hospital. "We need to know more. That is why studies like this are very important."

Although older facilities still use round-the-clock lighting, modern NICUs, like that at Vanderbilt, cycle their lighting in a day/night cycle and keep lighting levels as low as possible, Walsh said. Also, covers are kept over the isolets that hold the babies in an effort to duplicate the dark conditions of the womb.

The finding that exposure to constant light disrupts the developing biological clock in baby mice provides an underlying mechanism that helps explain the results of several previous clinical studies. One found that infants from neonatal units with cyclic lighting tend to begin sleeping through the night more quickly than those from units with constant lighting. Other studies have found that infants placed in units that maintain a day/night cycle gain weight faster than those in units with constant light.

The research is a follow-up from a study that the McMahon group published last year which found that long periods of constant light disrupt the synchronization of the biological clock in adult mice. In all mammals, including mice and humans, the master biological clock is located in an area of the brain called the suprachiasmatic nuclei (SCN). It influences the activity of a surprising number of organs, including the brain, heart, liver and lungs and regulates the daily activity cycles known as circadian rhythms.