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A geriatric resident reads in the "winter garden room" at the Institut Universitaire de Geriatre de Montreal in Montreal on March 8, 2019.Christinne Muschi/The Globe and Mail

A long-term care facility in Quebec is helping to shed light on a tantalizing question: Could opening the curtains more often improve cognitive function in patients with dementia?

The study is one of two led by Dr. Julie Carrier, professor of the psychology department at the University of Montreal, to test the effects of light therapy on older adults with cognitive impairment.

Scientists have long recognized that changes in light exposure can alter one’s circadian rhythm, including sleep-wake cycles. Now, they’re also learning about the mechanisms involved in the direct, stimulating effects of light on the brain – the kind of instant clearing of the cobwebs that happens when you step outside on a sunny day.

Increasing their exposure to light “doesn’t cost that much, but could make a major difference in the behaviour and well-being of the patients,” said Dr. Carrier, who is also the scientific director of the Canadian Sleep and Circadian Network.

Yet, she says, some long-term care facilities keep patients in dimly lit environments, in part, due to the unproven belief that bright lighting may cause those with dementia to become agitated.

At L’Institut universitaire de gériatrie de Montréal, a health centre for seniors affiliated with the University of Montreal that provides long-term residential care, she plans to introduce measures, such as allowing in more sunlight through the windows and switching to brighter light fixtures. In the study, which is expected to launch soon, she will assess whether this helps regulate patients’ sleep-wake cycles, which are often disturbed with dementia, and boosts their mood and daytime alertness.

In a separate study, Dr. Carrier is asking patients with Parkinson’s disease to wear special light-therapy glasses, which resemble a visor with a built-in lamp. She emphasizes light exposure cannot slow the degenerative process of this disease, but she believes about four hours a day of wearing the glasses may help combat drowsiness, a symptom that can be challenging for many patients.

In this way, light could be “like using caffeine to increase vigilance,” she said.

These studies build on research Dr. Carrier and her colleagues have conducted in recent years to examine why people generally become less responsive to light as they age. It takes longer for the circadian rhythm of older adults to adjust to changes in light, which tends to make it more difficult for them to overcome jet lag, for example, she explained. Older adults also tend to be less responsive to the direct effects of light on mood and alertness.

This decline in light-sensitivity appears to occur in the brain, rather than in the eyes, she says. With brain imaging, she and her research team found adults over the age of 65 had less activity in certain regions of the brain when stimulated with light, compared with participants in their 20s, regardless of whether they had undergone cataract surgery to replace cloudy, yellowed lenses with clear new ones.

But perhaps, she suggests, diminished light sensitivity could be offset with greater light exposure.

“Everybody needs light in order to be in tune with the environment and to be stimulated, et cetera, but it will be even more important [in older adults] because their brain is less responsive,” she said.

At Michigan State University, Dr. Lily Yan, who is not involved in Dr. Carrier’s research, says her own work with animal models has led her to believe light therapy could be beneficial for older adults.

Dr. Yan, an associate professor of psychology, conducts experiments on Nile grass rats, a specific type of rat which, like humans, is diurnal, or active during the day. She found that when the rats were kept in dim lighting, they exhibited impaired spatial learning memory. That is, they fared worse on a maze test. Moreover, she and her colleagues found that after four weeks, the rodents had a reduction of spine density, or a loss of synapse connections, in certain areas of their hippocampus, a part of the brain involved in spatial navigation and formation of memories.

Four weeks after being returned to brighter lighting conditions, the rats’ cognitive deficits recovered and the structural changes to their hippocampus returned to normal.

Upon reviewing these findings, Dr. Yan said: “The first thing that came to mind was we should definitely improve the lighting conditions in …nursing homes" so as not to contribute to residents’ cognitive decline.

She noted long-term care residents who are not able to get outside regularly may be particularly lacking in light exposure.

While she says the discovery that rats’ brains could bounce back is “really good news,” Dr. Yan pointed out the animals used in her study were young and healthy. It’s unclear whether older rats would respond the same way, let alone older humans.

Still, she notes, mood and cognitive function have been shown to fluctuate with light exposure in humans with seasonal affective disorder. Other researchers have also found seasonal fluctuations in symptoms of Alzheimer’s disease in older adults, which may be related to seasonal changes in light. A study published in the journal PLOS Medicine last year led by researchers at the University of Toronto, for example, found older adults were more likely to meet diagnostic criteria for mild cognitive impairment or dementia in winter and spring than in the summer or fall.

Nevertheless, there are still many unanswered questions about the effects of light on the brain. While light therapy has been shown to help boost mood and energy in individuals with depression, it is unknown how much light is optimal for healthy adults, says Dr. Kathryn Roecklein, an associate professor of psychology at the University of Pittsburgh. She adds she is not aware of any evidence that light exposure prevents cognitive decline.

And although the risks are small, Dr. Roecklein says, light therapy can include similar risks to antidepressant medication, such as a chance of a manic episode in people with undetected bipolar disorder, as well as headaches, eye fatigue, a sense of feeling “wired” or insomnia.

Dr. Yan, meanwhile, says she believes light exposure can benefit aging brains. “But to [what] extent? That is the question.”

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