What Color is Your Night Light? It May Affect Your Mood

Study Finds Red Light Least Harmful, While Blue Light is Worst

When it comes to some of the health hazards of light at night, a new study suggests that the color of the light can make a big difference.

In a study involving hamsters, researchers found that blue light had the worst effects on mood-related measures, followed closely by white light.

But hamsters exposed to red light at night had significantly less evidence of depressive-like symptoms and changes in the brain linked to depression, compared to those that experienced blue or white light.

The only hamsters that fared better than those exposed to red light were those that had total darkness at night.

The findings may have important implications for humans, particularly those whose work on night shifts makes them susceptible to mood disorders, said Randy Nelson, co-author of the study and professor of neuroscience and psychology at The Ohio State University.

“Our findings suggest that if we could use red light when appropriate for night-shift workers, it may not have some of the negative effects on their health that white light does,” Nelson said.

The study appears in the Aug. 7, 2013, issue of The Journal of Neuroscience.

The research examined the role of specialized photosensitive cells in the retina — called ipRGCs — that don’t have a major role in vision, but detect light and send messages to a part of the brain that helps regulate the body’s circadian clock. This is the body’s master clock that helps determine when people feel sleepy and awake.

Other research suggests these light-sensitive cells also send messages to parts of the brain that play a role in mood and emotion.

“Light at night may result in parts of the brain regulating mood receiving signals during times of the day when they shouldn’t,” said co-author Tracy Bedrosian, a former graduate student at Ohio State who is now a postdoctoral researcher at the Salk Institute. “This may be why light at night seems to be linked to depression in some people.”

What people experience as different colors of light are actually lights of different wavelengths. The ipRGCs don’t appear to react to light of different wavelengths in the same way.

“These cells are most sensitive to blue wavelengths and least sensitive to red wavelengths,” Nelson said. “We wanted to see how exposure to these different color wavelengths affected the hamsters.”

In one experiment, the researchers exposed adult female Siberian hamsters to four weeks each of nighttime conditions with no light, dim red light, dim white light (similar to that found in normal light bulbs) or dim blue light.

They then did several tests with the hamsters that are used to check for depressive-like symptoms. For example, if the hamsters drink less-than-normal amounts of sugar water — a treat they normally enjoy — that is seen as evidence of a mood problem.

Results showed that hamsters that were kept in the dark at night drank the most sugar water, followed closely by those exposed to red light. Those that lived with dim white or blue light at night drank significantly less of the sugar water than the others.

After the testing, the researchers then examined the hippocampus regions of the brains of the hamsters.

Hamsters that spent the night in dim blue or white light had a significantly reduced density of dendritic spines compared to those that lived in total darkness or that were exposed to only red light. Dendritic spines are hairlike growths on brain cells that are used to send chemical messages from one cell to another. 

A lowered density of these dendritic spines has been linked to depression, Nelson said.

“The behavior tests and changes in brain structure in hamsters both suggest that the color of lights may play a key role in mood,” he said.

“In nearly every measure we had, hamsters exposed to blue light were the worst off, followed by those exposed to white light,” he said. “While total darkness was best, red light was not nearly as bad as the other wavelengths we studied.”

Nelson and Bedrosian said they believe these results may be applicable to humans.

In addition to shift workers, others may benefit from limiting their light at night from computers, televisions and other electronic devices, they said. And, if light is needed, the color may matter.

“If you need a night light in the bathroom or bedroom, it may be better to have one that gives off red light rather than white light,” Bedrosian said.

Sleep deprivation linked to junk food cravings

A sleepless night makes us more likely to reach for doughnuts or pizza than for whole grains and leafy green vegetables, suggests a new study from UC Berkeley that examines the brain regions that control food choices. The findings shed new light on the link between poor sleep and obesity.

Using functional magnetic resonance imaging (fMRI), UC Berkeley researchers scanned the brains of 23 healthy young adults, first after a normal night’s sleep and next, after a sleepless night. They found impaired activity in the sleep-deprived brain’s frontal lobe, which governs complex decision-making, but increased activity in deeper brain centers that respond to rewards. Moreover, the participants favored unhealthy snack and junk foods when they were sleep deprived.

“What we have discovered is that high-level brain regions required for complex judgments and decisions become blunted by a lack of sleep, while more primal brain structures that control motivation and desire are amplified,” said Matthew Walker, a UC Berkeley professor of psychology and neuroscience and senior author of the study published today (Tuesday, Aug. 6) in the journal Nature Communications.

Moreover, he added, “high-calorie foods also became significantly more desirable when participants were sleep-deprived. This combination of altered brain activity and decision-making may help explain why people who sleep less also tend to be overweight or obese.”

Previous studies have linked poor sleep to greater appetites, particularly for sweet and salty foods, but the latest findings provide a specific brain mechanism explaining why food choices change for the worse following a sleepless night, Walker said.

“These results shed light on how the brain becomes impaired by sleep deprivation, leading to the selection of more unhealthy foods and, ultimately, higher rates of obesity,” said Stephanie Greer, a doctoral student in Walker’s Sleep and Neuroimaging Laboratory and lead author of the paper. Another co-author of the study is Andrea Goldstein, also a doctoral student in Walker’s lab.

In this newest study, researchers measured brain activity as participants viewed a series of 80 food images that ranged from high-to low-calorie and healthy and unhealthy, and rated their desire for each of the items. As an incentive, they were given the food they most craved after the MRI scan.

Food choices presented in the experiment ranged from fruits and vegetables, such as strawberries, apples and carrots, to high-calorie burgers, pizza and doughnuts. The latter are examples of the more popular choices following a sleepless night.

On a positive note, Walker said, the findings indicate that “getting enough sleep is one factor that can help promote weight control by priming the brain mechanisms governing appropriate food choices.”

Breastfeeding may reduce Alzheimer’s risk

A new study suggests that mothers who breastfeed run a lower risk of developing Alzheimer’s, with longer periods of breastfeeding further reducing the risk.

Mothers who breastfeed their children may have a lower risk of developing Alzheimer’s Disease, with longer periods of breastfeeding also lowering the overall risk, a new study suggests.

The report, newly published in the Journal of Alzheimer’s Disease, suggests that the link may be to do with certain biological effects of breastfeeding. For example, breastfeeding restores insulin tolerance which is significantly reduced during pregnancy, and Alzheimer’s is characterised by insulin resistance in the brain.

Although they used data gathered from a very small group of just 81 British women, the researchers observed a highly significant and consistent correlation between breastfeeding and Alzheimer’s risk. They argue that this was so strong that any potential sampling error was unlikely.

At the same time, however, the connection was much less pronounced in women who already had a history of dementia in their family. The research team hope that the study – which was intended merely as a pilot – will stimulate further research looking at the relationship between female reproductive history and disease risk.

The findings may point towards new directions for fighting the global Alzheimer’s epidemic – especially in developing countries where cheap, preventative measures are desperately needed.

More broadly, the study opens up new lines of enquiry in understanding what makes someone susceptible to Alzheimer’s in the first place. It may also act as an incentive for women to breastfeed, rather than bottle-feed – something which is already known to have wider health benefits for both mother and child.

Dr Molly Fox, from the Department of Biological Anthropology at the University of Cambridge, who led the study, said: “Alzheimer’s is the world’s most common cognitive disorder and it already affects 35.6 million people. In the future, we expect it to spread most in low and middle-income countries. So it is vital that we develop low-cost, large-scale strategies to protect people against this devastating disease.”

Previous studies have already established that breastfeeding can reduce a mother’s risk of certain other diseases, and research has also shown that there may be a link between breastfeeding and a woman’s general cognitive decline later in life. Until now, however, little has been done to examine the impact of breastfeeding duration on Alzheimer’s risk.

Fox and her colleagues – Professor Carlo Berzuini and Professor Leslie Knapp – interviewed 81 British women aged between 70 and 100. These included both women with, and without, Alzheimer’s. In addition, the team also spoke to relatives, spouses and carers.

Through these interviews, the researchers collected information about the women’s reproductive history, their breastfeeding history, and their dementia status. They also gathered information about other factors that might account for their dementia, for example, a past stroke, or brain tumour.

Dementia status itself was measured using a standard rating scale called the Clinical Dementia Rating (CDR). The researchers also developed a method for estimating the age of Alzheimer’s sufferers at the onset of their disease, using the CDR as a basis and taking into account their age and existing, known patterns of Alzheimer’s progression. All of this information was then compared with the participants’ breastfeeding history.

Despite the small number of participants, the study revealed a number of clear links between breastfeeding and Alzheimer’s. These were not affected when the researchers took into account other potential variables such as age, education history, the age when the woman first gave birth, her age at menopause, or her smoking and drinking history.

The researchers observed three main trends:

• Women who breastfed exhibited a reduced Alzheimer’s Disease risk compared with women who did not.

• Longer breastfeeding history was significantly associated with a lower Alzheimer’s Risk.

• Women who had a higher ratio of total months pregnant during their life to total months breastfeeding had a higher Alzheimer’s risk.

The trends were, however, far less pronounced for women who had a parent or sibling with dementia. In these cases, the impact of breastfeeding on Alzheimer’s risk appeared to be significantly lower, compared with women whose families had no history of dementia.

The study argues that there may be a number of biological reasons for the connection between Alzheimer’s and breastfeeding, all of which require further investigation.

One theory is that breastfeeding deprives the body of the hormone progesterone, compensating for high levels of progesterone which are produced during pregnancy. Progesterone is known to desensitize the brain’s oestrogen receptors, and oestrogen may play a role in protecting the brain against Alzheimer’s.

Another possibility is that breastfeeding increases a woman’s glucose tolerance by restoring her insulin sensitivity after pregnancy. Pregnancy itself induces a natural state of insulin resistance. This is significant because Alzheimer’s is characterised by a resistance to insulin in the brain (and therefore glucose intolerance) to the extent that it is even sometimes referred to as “Type 3 diabetes”.

“Women who spent more time pregnant without a compensatory phase of breastfeeding therefore may have more impaired glucose tolerance, which is consistent with our observation that those women have an increased risk of Alzheimer’s disease,” Fox added.

Are we there yet?

MIT researchers reveal how the brain keeps eyes on the prize.

“Are we there yet?”

As anyone who has traveled with young children knows, maintaining focus on distant goals can be a challenge. A new study from MIT suggests how the brain achieves this task, and indicates that the neurotransmitter dopamine may signal the value of long-term rewards. The findings may also explain why patients with Parkinson’s disease — in which dopamine signaling is impaired — often have difficulty in sustaining motivation to finish tasks.

The work is described this week in the journal Nature.

Previous studies have linked dopamine to rewards, and have shown that dopamine neurons show brief bursts of activity when animals receive an unexpected reward. These dopamine signals are believed to be important for reinforcement learning, the process by which an animal learns to perform actions that lead to reward.

Taking the long view

In most studies, that reward has been delivered within a few seconds. In real life, though, gratification is not always immediate: Animals must often travel in search of food, and must maintain motivation for a distant goal while also responding to more immediate cues. The same is true for humans: A driver on a long road trip must remain focused on reaching a final destination while also reacting to traffic, stopping for snacks, and entertaining children in the back seat.

The MIT team, led by Institute Professor Ann Graybiel — who is also an investigator at MIT’s McGovern Institute for Brain Research — decided to study how dopamine changes during a maze task approximating work for delayed gratification. The researchers trained rats to navigate a maze to reach a reward. During each trial a rat would hear a tone instructing it to turn either right or left at an intersection to find a chocolate milk reward.

Rather than simply measuring the activity of dopamine-containing neurons, the MIT researchers wanted to measure how much dopamine was released in the striatum, a brain structure known to be important in reinforcement learning. They teamed up with Paul Phillips of the University of Washington, who has developed a technology called fast-scan cyclic voltammetry (FSCV) in which tiny, implanted, carbon-fiber electrodes allow continuous measurements of dopamine concentration based on its electrochemical fingerprint.

“We adapted the FSCV method so that we could measure dopamine at up to four different sites in the brain simultaneously, as animals moved freely through the maze,” explains first author Mark Howe, a former graduate student with Graybiel who is now a postdoc in the Department of Neurobiology at Northwestern University. “Each probe measures the concentration of extracellular dopamine within a tiny volume of brain tissue, and probably reflects the activity of thousands of nerve terminals.”

Gradual increase in dopamine

From previous work, the researchers expected that they might see pulses of dopamine released at different times in the trial, “but in fact we found something much more surprising,” Graybiel says: The level of dopamine increased steadily throughout each trial, peaking as the animal approached its goal — as if in anticipation of a reward.

The rats’ behavior varied from trial to trial — some runs were faster than others, and sometimes the animals would stop briefly — but the dopamine signal did not vary with running speed or trial duration. Nor did it depend on the probability of getting a reward, something that had been suggested by previous studies.

“Instead, the dopamine signal seems to reflect how far away the rat is from its goal,” Graybiel explains. “The closer it gets, the stronger the signal becomes.” The researchers also found that the size of the signal was related to the size of the expected reward: When rats were trained to anticipate a larger gulp of chocolate milk, the dopamine signal rose more steeply to a higher final concentration.

In some trials the T-shaped maze was extended to a more complex shape, requiring animals to run further and to make extra turns before reaching a reward. During these trials, the dopamine signal ramped up more gradually, eventually reaching the same level as in the shorter maze. “It’s as if the animal were adjusting its expectations, knowing that it had further to go,” Graybiel says.

An ‘internal guidance system’

“This means that dopamine levels could be used to help an animal make choices on the way to the goal and to estimate the distance to the goal,” says Terrence Sejnowski of the Salk Institute, a computational neuroscientist who is familiar with the findings but who was not involved with the study. “This ‘internal guidance system’ could also be useful for humans, who also have to make choices along the way to what may be a distant goal.”

One question that Graybiel hopes to examine in future research is how the signal arises within the brain. Rats and other animals form cognitive maps of their spatial environment, with so-called “place cells” that are active when the animal is in a specific location. “As our rats run the maze repeatedly,” she says, “we suspect they learn to associate each point in the maze with its distance from the reward that they experienced on previous runs.”

As for the relevance of this research to humans, Graybiel says, “I’d be shocked if something similar were not happening in our own brains.” It’s known that Parkinson’s patients, in whom dopamine signaling is impaired, often appear to be apathetic, and have difficulty in sustaining motivation to complete a long task. “Maybe that’s because they can’t produce this slow ramping dopamine signal,” Graybiel says. 

Questions answered with the pupils of your eyes

Patients who are otherwise completely unable to communicate can answer yes or no questions within seconds with the help of a simple system—consisting of just a laptop and camera—that measures nothing but the size of their pupils. The tool, described and demonstrated in Current Biology, a Cell Press publication, on August 5 takes advantage of changes in pupil size that naturally occur when people do mental arithmetic. It requires no specialized equipment or training at all.

The new pupil response system might not only help those who are severely motor-impaired communicate, but might also be extended to assessing the mental state of patients whose state of consciousness is unclear, the researchers say.

"It is remarkable that a physiological system as simple as the pupil has such a rich repertoire of responses that it can be used for a task as complex as communication," says Wolfgang Einhäuser of Philipps-Universität Marburg in Germany.

The researchers asked healthy people to solve a math problem only when the correct answer to a yes or no question was shown to them on a screen. The mental load associated with solving that problem caused an automatic increase in pupil size, which the researchers showed they could measure and translate into an accurate answer to questions like “Are you 20 years old?”

They then tested out their pupil response algorithm on seven “typical” locked-in patients who had suffered brain damage following a stroke. In many cases, they were able to discern an answer based on pupil size alone.

"We find it remarkable that the system worked almost perfectly in all healthy observers and then could be transferred directly from them to the patients, with no need for training or parameter adjustment," Einhäuser says.

While the system could still use improvement in terms of speed and accuracy, those are technical hurdles Einhäuser is confident they can readily overcome. Their measures of pupil response could already make an important difference for those who need it most.

"For patients with altered state of consciousness—those who are in a coma or other unresponsive state—any communication is a big step forward," he says.