One of the first symptoms seen in people with Alzheimer's is disturbances in sleep patterns, including daytime sleepiness, evening agitation or confusion, long periods of sleeplessness, and frequent waking during the night. These changes are thought to be the result of damage to areas of the brain that regulate sleep.
Alzheimer's patients also tend to spend less time in both REM (rapid eye movement) sleep, in which 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, dreamless sleep characterized by slow "delta" brain waves (0.1 to 3.5 Hz), when Daytime memories are consolidated.
A scientific team led by experts from North Carolina, USA, has now shown that the same reduction in sleep time and delta brain waves occurs in dogs with the canine equivalent of dementia, Cognitive Dysfunction Syndrome. canine (CCDS). These dogs sleep less and less soundly. The results of this study have been published in the journal Frontiers in Veterinary Science.
"Our study is the first to assess the association between cognitive decline and sleep using polysomnography, the same technique used in human sleep studies, in older dogs," said lead author Natasha Olby, a professor of veterinary neurology and neurosurgery at North Carolina State University (USA).
Olby's team studied 28 mixed and purebred male and female dogs between the ages of 10.4 and 16.2 years, which corresponds to between 81% and 106% of their average lifespan, according to the study. size. Their owners were asked to complete a questionnaire about their canine companions, to rate the severity of CCDS symptoms, such as disorientation, poor social interactions, and house soiling. The researchers also examined the dogs for possible orthopedic, neurological, biochemical, and physiological comorbidities.
The results of the study indicate that eight of the dogs tested (28.5%) were classified as normal, while another eight (28.5%) had mild CCDS, four (14.3%) moderate, and eight (28.5%). %) had severe CCDS.
The researchers performed a series of cognitive tests on the dogs to measure their attention, working memory, and executive control. For example, in the "diversion task", a dog had to retrieve a treat from a horizontal transparent cylinder by accessing it from either end; this task is made more difficult by blocking their preferred side, so they have to show cognitive skills, flexibility to deviate to the other end of the cylinder.
Alejandra Mondino. The first signatory to the study and a postdoctoral student in Professor Olby's research group, she explained that the team conducted polysomnography studies in a quiet room with dim lighting and white noise in a "sleep clinic." The dogs were allowed to take a spontaneous nap at noon, while the electrodes measured their brain waves, electrical activity of the muscles and heart, and eye movements. These measurements lasted 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 drowsiness, 24 (86%) entered NREM sleep, while 15 (54%) entered REM sleep.
The results showed that dogs with higher dementia scores, and dogs that did better on the diverting task, took longer to fall asleep and spent less time sleeping, and this was true for both NREM and sleep. the REM.
Dogs with lower memory scores showed changes, such as fewer slow oscillations in their EEGs, during REM sleep, indicating that they slept less soundly during this phase.
"In people, slow brain oscillations are characteristic of SWS and are related to the activity of the so-called 'glymphatic system', a transport system that removes protein waste products from the cerebrospinal fluid," said Professor Olby.
"The reduction in slow oscillations in people with Alzheimer's and the associated reduction in the elimination of these toxins has been linked to worse memory consolidation during deep sleep."
In contrast, dogs with poorer 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 soundly.
Dogs that did worse on the "gaze hold" task, which measures attention span, showed tighter coupling in delta waves between the two brain hemispheres, a result 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 resemble those found in people with Alzheimer's. But they caution that it is not yet known whether these changes also occur when dogs sleep at night rather than in the afternoon.
"Our next step will be to follow the dogs over time throughout their adulthood and later life to determine if there are early markers in their sleep-wake patterns, or in the electrical activity of their brain during sleep, that could predict the future development of cognitive dysfunction", details Professor Olby in a note released by her university.