Old dogs afflicted with dementia experience less restful sleep, similarly to individuals with Alzheimer’s.

In people with Alzheimer’s disease, the early symptoms are usually disturbances in sleep rhythms. These include daytime sleepiness, showing agitation or confusion around dusk, staying awake longer, and waking up more often at night. These changes are thought to result from damage to the sleep-regulating areas of the brain. Alzheimer’s patients tend to spend less time in rapid eye movement (REM) sleep, which is when most dreams occur, and non-REM (NREM) sleep. But they show the greatest reduction in so-called slow-wave sleep (SWS)—a stage of deep, non-dreaming sleep, characterized by slow “delta” brain waves (0.1 to 3.5 Hz)—when memories of the day are consolidated.

Now, scientists have shown that the same decrease in sleep time and delta brain waves occurs in dogs with the dementia, Canine Cognitive Dysfunction Syndrome (CCDS). Consequently, these dogs sleep less and less deeply. The results are published in Frontiers in Veterinary Science.

“Our study is the first to evaluate the relationship between cognitive impairment and sleep using polysomnography — the same technique used in sleep studies of people — in geriatric dogs,” said lead researcher Dr. Natasha Olby, professor of veterinary neurology and neurosurgery at North Carolina State University.

Elderly dogs with or without dementia

Olby and colleagues studied 28 female and male mixed-bred and full-bred dogs between the ages of 10.4 and 16.2 years, which equates to between 81% and 106% of their average lifespan, depending on size. Owners were asked to fill out a questionnaire about their canine companions, rating the severity of CCDS symptoms such as confusion, poor social interactions, and house soiling. The researchers also examined the dogs for possible orthopedic, neurological, biochemical and physiological diseases.

Based on the results, eight dogs (28.5%) were classified as normal, while another eight dogs (28.5%), four (14.3%), and eight (28.5%) had mild, moderate, or severe CCDS, respectively.

The researchers then administered a series of cognitive tests to the dogs, measuring attention, working memory, and executive control. For example, in the ‘wrap task’ the dog had to retrieve a treat from a horizontal transparent cylinder by reaching for it from either end – this task was then made more difficult by blocking it or their preferred side so they had to show perceptive flexibility in turning to the other end of the cylinder.

Dog sleep clinic

Next, first author Dr. Alejandra Mondino (a postdoctoral fellow in Olby’s research group) and colleagues conducted polysomnography studies in a quiet room with dim lighting and white noise in a “sleep clinic.” The dogs were allowed to spontaneously take an afternoon nap, while the electrodes measured brain waves, electrical activity of muscles, heart and eye movements. These measurements continued for up to two hours, but were stopped if the dogs became anxious, tried to leave the room, or removed the electrodes. 26 (93%) dogs entered sleepiness, 24 (86%) entered NREM sleep, and 15 (54%) entered REM sleep.

Results showed that dogs who had higher dementia scores, and dogs who did better on the turning task, took longer to fall asleep and spent less time sleeping, and this was true for both NREM and REM sleep.

Dogs with poor memory results showed changes, such as fewer slow oscillations in the EEG, during REM sleep, indicating that they were sleeping less deeply during this stage.

“In humans, slow oscillations of the brain are characteristic of SWS and are associated with activity of the so-called ‘glymphatic system,’ a transport system that removes protein waste from the cerebrospinal fluid,” Olby said.

“The decrease in slow oscillations in people with Alzheimer’s disease, and the associated reduced removal of these toxins, has a role in the impairment of memory consolidation during deep sleep.”

In contrast, dogs with poor memory had more pronounced fast beta waves, between 15.75 and 19 Hz. Strong beta waves are typical of wakefulness in healthy people and dogs, so they are not a normal phenomenon during sleep – again indicating that dogs with CCDS sleep less deeply.

Daytime sleep versus night sleep

Dogs that performed worse on the “continuous gaze” task, which measures attention span, showed tighter coupling of delta waves between the two hemispheres of the brain — a finding that has also been found in people with dementia.

The authors concluded that dogs with CCDS showed changes in the sleep-wake cycle during the experiments that were similar to those in people with Alzheimer’s disease. But they caution that it is still not known if these changes also occur while dogs sleep at night rather than in the afternoon.

“Our next step will be to follow the dogs over time through their adult and older years to determine if there are any early signs in their patterns of wakefulness during sleep, or in the electrical activity of their brain during sleep, that could predict the future development of cognitive impairment,” Olby said.