Discovery of Mysterious Brain Waves Linked to Memory Loss

Arabia.net – Episodic memory, which allows for the retrieval of events from a person’s life, underpins the recall of personal experiences such as the first day of school or an event that occurred minutes ago, like where a car was parked in a parking lot. These memories help form the foundation of long-term memory, whether related to a prominent teacher from childhood or the location where a set of keys or a handbag was left just moments ago.

According to a report published on Science Daily, this ability tends to weaken with age, making it more difficult to retrieve scenes, sounds, and other details associated with past experiences. Scientists still do not fully understand why this occurs.

A new study conducted by researchers at the University of California and published in the journal Nature Neuroscience provides important insights into what may be happening in the brain as it ages. Neuroscientist Omer Sharon and his colleagues, under the supervision of former University of California sleep researcher Matthew Walker, discovered a link between disruptions in brain wave activity during deep sleep, declining memory performance, and the accumulation of tau protein, a protein associated with Alzheimer’s disease. The findings suggest that the accumulation of tau protein in the brain’s frontal cortex is linked to changes in the coordinated electrical activity that helps consolidate memories throughout the night.

Researcher Sharon stated that this is “the first time this relationship between tau protein and its negative impact on memory consolidation through the weakening of slow-moving waves originating in the frontal cortex has been demonstrated.”

Sleep involves distinct stages, each associated with different patterns of brain activity. Rapid Eye Movement (REM) sleep is particularly notable because the eyes move beneath closed eyelids, and most dreaming occurs during this stage. However, another stage, known as Non-Rapid Eye Movement (NREM) sleep, is crucial for maintaining healthy brain function.

During this deep stage of sleep, when dreaming is limited or absent, large groups of nerve cells briefly stop functioning and then resume activity in a coordinated sequence. These synchronized changes produce slow electrical waves that spread throughout the brain, typically starting from the frontal cortex.

Researcher Sharon explained, “Each slow wave reflects a vast number of nerve cells that stop functioning and then resume activity together. The new study shows that for memory, it is essential for these events to occur sequentially across large parts of the brain. This coordinated cessation of activity is observed only during deep sleep and may be one of the reasons for sleep.”

The researchers found that this highly organized activity becomes less coordinated as tau protein accumulates in the brain with age. Instead of waves moving together across wide areas, they become more scattered and cover shorter distances. These changes are associated with impaired memory consolidation, declining cognitive abilities, and Alzheimer’s disease.

To verify this relationship, the scientists monitored brain activity during sleep using electroencephalography (EEG). They compared cognitively healthy young adults in their early twenties with older participants aged between their mid-sixties and mid-seventies.

The differences were striking. In the younger participants, groups of slow waves moved together over distances roughly equivalent to the width of a hand on the scalp. In contrast, among older adults, the waves typically covered shorter distances and appeared more independently, rather than moving in coordinated groups.

The research team also examined whether these changes were associated with the accumulation of tau protein. In collaboration with Dr. William Jagust, Professor Emeritus of Public Health and Neuroscience at the University of California, the researchers used positron emission tomography (PET) imaging to examine the brains of older participants. This imaging technique relies on the injection of radioactive tracers into the bloodstream to detect biological activity and the distribution of specific substances.

The scans revealed that tau protein accumulation in the prefrontal cortex was linked to disruptions in the longer brain waves that typically occur during deep sleep. Notably, these changes were present in individuals who had not developed Alzheimer’s disease.