A night without sleep increases markers of connectivity between brain cells, suggesting that sleep in humans may be important in restoring the brain’s cellular balance, according to research published June 23 in an open access journal. PLOS Biology By David Elmenhorst and colleagues at the Jülich Institute for Neuroscience and Medicine in North Rhine-Westphalia, Germany.
Scientists have long wondered why humans and other animals need to sleep. One possible mechanism is that sleep is necessary to restore synaptic connections and homeostasis in the brain. Synapses (connections between brain cells) are strengthened during wakefulness. This increases the amount of energy required by the brain and leads to the accumulation of proteins in the brain. Sleep is thought to reset these levels, reduce synaptic connections, and restore homeostasis, but so far evidence is limited to animal models. To determine whether the synaptic homeostasis hypothesis in humans is supported, the study authors used positron emission tomography (PET) to look for markers of synaptic vesicle glycoprotein 2A (SV2A), a marker of brain synapses, in 40 participants, half of whom did not sleep through the night.
The authors found that after 28 hours of continuous wakefulness, the sleep-deprived group had higher SV2A measurements in several brain regions, including the hippocampus (an area important for memory) and the thalamus (an important information relay in the brain). When sleep-deprived participants were allowed to take a two-hour nap, higher levels of SV2A were associated with increased slow-wave activity during sleep, a marker of deep sleep and sleep pressure. Although SV2A is only a surrogate for brain cell connectivity and the increase was relatively small, the results support a synaptic homeostasis model of sleep and suggest a biological link between the need for sleep and the establishment of cellular connections.
The authors add: ”During sleep deprivation, the brain stays awake longer and continues to process stimuli and information. Our study shows that markers of synaptic density increase in several brain regions after approximately 28.5 hours of wakefulness. This suggests that sleep deprivation not only causes fatigue, but is also accompanied by measurable changes in neural connectivity.”
sauce:
Reference magazines:
Griffa, G. others. (2026). Learning involves both temporal and persistent cellular mechanisms in the human brain. PLOS Biology. DOI: 10.1371/journal.pbio.3003861. https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3003861
