A study published on June 23 found that a night without sleep produced increased markers of connections between brain cells, suggesting that sleep may be important for restoring cellular balance in the human brain. The research was conducted by David Elmenhorst from the Forschungszentrum Jülich Institute of Neuroscience and Medicine in North Rhine-Westphalia, Germany, and colleagues.
The scientists aimed to understand why humans and other animals need to sleep. One hypothesis is that sleep is required to restore synaptic connections and homeostasis in the brain. Synapses, which are the connections between brain cells, become stronger during wakefulness. This process increases energy demands and leads to protein buildup in the brain. Sleep is thought to reset these levels by reducing synaptic connections and restoring homeostasis; however, evidence supporting this theory has previously been limited to animal models.
To test whether this hypothesis holds true for humans, researchers used positron emission tomography (PET) scans to look for markers of synaptic vesicle glycoprotein 2A (SV2A), an indicator of brain synapses. The study involved 40 participants, half of whom went one night without sleep.
After 28 hours of continuous wakefulness, those who were sleep deprived showed higher measures of SV2A in several regions of the brain—including the hippocampus, which plays a key role in memory formation—and the thalamus, an important information relay center. When these participants were later allowed a two-hour nap, higher SV2A levels were associated with more slow wave activity during their rest—a marker linked with deep sleep and increased 'sleep pressure.' While SV2A serves only as a proxy for actual neural connections and its elevation was relatively small, these findings support the idea that lack of sleep results in measurable changes within neural networks.
The authors said, "During sleep deprivation, the brain remains awake longer and continues to process stimuli and information. Our study shows that after approximately 28.5 hours of wakefulness, a marker for synaptic density increases in several brain regions. This suggests that sleep deprivation not only causes fatigue but is also accompanied by measurable changes in neural connections."
