A single night of sleep deprivation increases levels of the synaptic density marker SV2A in the thalamus, hippocampus, and parietal cortex, according to a randomized PET imaging study published in PLoS Biology. The findings provide direct in vivo support for the synaptic homeostasis hypothesis in humans.
What they found
Forty healthy adults (mean age 27.5 years) underwent two [18F]SynVesT-1 PET scans on consecutive days. Half were randomly assigned to normal sleep and half to total sleep deprivation (approximately 28 hours of continuous wakefulness). Scans were performed at the same circadian time point to control for time-of-day effects.
Sleep deprivation led to significant increases in SV2A binding, a PET ligand that labels synaptic vesicle glycoprotein 2A and is commonly interpreted as a proxy for synaptic density:
- Thalamus: +4.6%
- Hippocampus: +5.6%
- Parietal cortex: +3.2%
No significant changes were observed in the control group across the same interval.
Importantly, the degree of SV2A increase correlated with elevated slow wave activity during recovery sleep — a well-established physiological marker of sleep pressure. This link directly ties the molecular imaging finding to a functional measure of sleep need.
Why it matters
The synaptic homeostasis hypothesis, proposed by Tononi and Cirelli, holds that wakefulness drives net synaptic potentiation (synapses grow stronger and more numerous), while sleep promotes synaptic down-selection and renormalization. Until now, direct in vivo evidence in humans has been limited.
This study shows that the human brain accumulates synaptic material during wakefulness at a detectable level within a single day, and that the magnitude of this accumulation predicts the intensity of subsequent slow wave activity. It also establishes SV2A PET as a tool sensitive enough to track sleep-wake dependent synaptic plasticity — opening the door for studies in insomnia, depression, and other conditions where synaptic homeostasis may be dysregulated.
Limits
SV2A is a proxy for synaptic density, not a direct measure of synaptic strength or number. The sample was young and healthy, so results may not generalize to older adults or clinical populations. The study measured one night of total sleep deprivation, which is an extreme condition relative to the partial sleep loss common in real life.
Bottom line
A single night of total sleep deprivation increases SV2A binding — a marker of synaptic density — in key brain regions. The accumulation predicts slow wave activity during recovery sleep, consistent with the synaptic homeostasis hypothesis.
Source
“Sleep deprivation increases levels of the synaptic density marker SV2A in the human brain.” PLoS Biology, June 23, 2026; 24(6): e3003816. DOI: 10.1371/journal.pbio.3003816