Alzheimer’s: the brain defends itself whilst sleeping and is more resilient thanks to ‘sleep spindles’
In people who sleep poorly, orexin levels rise, which has a negative effect. However, there are electrical currents that have the opposite effect. And these might facilitate memory. So far, only an association has been observed.
It is well known that getting too little sleep – and, above all, poor-quality sleep – increases the risk of developing cognitive decline and Alzheimer’s disease. But new research now suggests that the body may have some defence mechanisms built into the very rhythms of sleep itself. Let’s start from the beginning. In people who sleep too little and poorly, levels of a neurotransmitter called orexin – which is essential for regulating sleep and appetite – rise. And if there is a rise in this substance in people with Alzheimer’s disease, the risk of developing memory deficits and difficulty thinking increases – in short, those troubles associated with the ‘fog’ of the neurodegenerative disease that pervades the brain. But take note: the body appears to be able to activate protective mechanisms designed to make brain functions resilient and thus to protect itself as far as possible from neurodegeneration.
The study involved collaboration between specialists from various centres, coordinated by researchers at Concordia University, and was published in Neurology. It hypothesises that specific brain waves during sleep, known as sleep spindles, are associated with protection against excessive levels of orexin. In short, there appears to be a link between the levels of this neurotransmitter and markers of Alzheimer’s disease. Please note: “The study shows that in patients with Alzheimer’s, higher levels of orexin are associated with poorer cognitive performance,” explains Lino Nobili, President of the Italian Academy of Sleep Medicine and lecturer at the University of Genoa’s Gaslini Institute. Increased activity of sleep spindles and slow-wave oscillations appears to mitigate this relationship.”
Patients followed over time
The study monitored orexin levels in the cerebrospinal fluid of 60 adults with mild to moderate Alzheimer’s disease who were followed by experts at the University of Lleida over a three-year period. The participants spent a night at a specialist centre where their brain activity was recorded using overnight polysomnography. In addition, the following morning, samples of cerebrospinal fluid were taken to measure orexin and other known biomarkers of Alzheimer’s disease. Cognitive and neuropsychiatric assessments were then carried out at regular intervals over the following three years, enabling the researchers to examine how sleep, brain chemistry and cognitive decline changed over time. The result: as well as confirming the harmful role of excess levels of the neurotransmitter, the research also revealed a ‘natural’ countermeasure. Those who exhibited sleep spindles during non-REM sleep showed a slower rate of cognitive decline over time compared with those with weaker spindles. In short: this activity during sleep appears to provide natural resilience against the negative effects of high levels of orexin on cognition and mental health.
Sleep spindles and orexin
Sleep spindles are bursts of electrical activity in the brain. They help to block out external stimuli and noise, filtering out unnecessary information, and promote the transfer and organisation of memories. Orexin neurons activate the neurotransmitter systems associated with wakefulness, keeping us active and alert during the day. Not only that: this substance also regulates appetite, muscle tone, the stress response and heart rate. A deficiency in orexin can lead to type 1 narcolepsy, resulting in excessive daytime sleepiness and sudden loss of muscle tone. However, an excess of orexin can cause hypervigilance at night, making it difficult to rest. Nowadays, targeting orexin with specific medicines helps to reduce brain activity and promote sleep in cases of insomnia.
Prospects for treatment
According to a statement from the University by Arsenio Paez, one of the study’s authors, “thanks to these data, we can observe how the course of Alzheimer’s disease changes over time. Alzheimer’s is a very long-term process, so this gives us a clearer picture of how the condition may change over time and allows us to intervene at different stages of the disease”. It should be noted that drugs that block orexin are already used to treat insomnia and are being studied as potential therapies for Alzheimer’s disease. This study suggests that monitoring sleep spindles, slow-wave oscillations and orexin levels could help measure the progression of the disease and identify patients who might benefit from a specific treatment. But we must not get ahead of ourselves.
