Sleep is a complex and important process that goes beyond energy restoration. It is essential for an individual's physical and mental well-being, particularly for a number of brain functions, like how nerve cells communicate with each other.
Sleep-Related Brain Rhythms
In 2021, experts from Ludwig-Maximilians-Universität München have investigated how memories are consolidated during sleep. Led by Dr. Thomas Schreiner, the researchers had shown the direct relationship between the emergence of sleep-related brain activity patterns and the reactivation of memory contents during sleep. However, it was not clear whether a central pacemaker orchestrated such rhythms.
To answer this question, the team collaborated with scientists from the University of Oxford and the Max Planck Institute for Human Development to help them reanalyze the data. Their investigation has identified respiration as a potential pacemaker. Their research findings are discussed in the paper "Respiration modulates sleep oscillations and memory reactivation in humans."
In this study, 20 participants were shown 120 images throughout two sessions. All the pictures were connected with particular words. The participants are then asked to sleep for around two hours in the sleep laboratory. When they awoke, the participants were questioned about the associations they had learned. During the entire period of learning and sleeping, the experts recorded their brain activity and breathing patterns.
It was discovered that previously learned contents were spontaneously reactivated by the sleeping brain of the participants during the presence of slow oscillations and sleep spindles. According to Schreiner, the precision of the coupling of these sleep-related brain rhythms increases from childhood to adolescence and declines again during adulthood.
Since the frequency of breathing also changes with age, the researchers analyzed the data in relation to the recorded breathing, establishing a connection between these factors. The results of their study reveal that a person's breathing and the emergence of characteristic slow oscillation and spindle patterns are linked.
While other studies have already established a relationship between breathing and cognition during wake, this research clarifies that respiration is also important for memory processing while asleep.
Older people usually suffer from respiratory disorders, sleep disorders, and declining memory functions. Schreiner and his colleagues plan to investigate further whether there are connections between these phenomena and whether some interventions make sense from a cognitive perspective.
Sleep Spindles Mechanisms
Sleep spindles refer to burstlike signals in the electroencephalogram (EEG) of the sleeping mammalian brain, as well as the electrical surface correlates of neuronal oscillations in the thalamus. This sequence of 10-15 Hz sinusoidal cycles is considered one of the most inheritable sleep EEG signatures.
Also known as "sigma bands" or "sigma waves," spindles are important in sensory processing and long-term memory construction. It is believed that the organization of spindles enables the neurons to communicate across cortices.
The density of the sleep spindle correlates with markers of intelligence and several neurological disorders that lead to cognitive deficits and dementia. Understanding their spatiotemporal distribution can have the potential for diagnostic purposes.
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