A short afternoon nap recalibrates both homeostatic and associative synaptic plasticity in the human cortex, as evidenced by reduced net synaptic strength and increased inducibility of LTP-like plasticity following nap compared to wake.
Key Findings
Results
A short afternoon nap reduced net synaptic strength compared to wakefulness, as indexed by higher TMS intensity needed to induce motor evoked potentials.
Twenty healthy adults participated in a repeated measures sleep laboratory study with an adaptation session and two experimental sessions (nap and wake, 1:15–2:15 pm).
Corticospinal excitability was assessed using transcranial magnetic stimulation (TMS)-probed motor evoked potentials (MEPs).
Higher TMS intensity was needed to induce MEPs after the nap session compared to the wake session, indicating reduced net synaptic strength.
This finding is consistent with the synaptic homeostasis hypothesis, which predicts that sleep downscales net synaptic strength built up during wakefulness.
Results
Wake EEG theta activity was reduced after the nap compared to wakefulness, providing a second index of reduced net synaptic strength following sleep.
Wake EEG theta activity was used as a non-invasive index of net synaptic strength.
Lower theta activity was observed following the nap session compared to the wake session.
Theta activity during wakefulness is thought to reflect cortical synaptic load, with higher activity indicating greater net synaptic strength.
The reduction in theta activity after nap parallels findings previously reported for nighttime sleep.
Results
The inducibility of associative (LTP-like) synaptic plasticity was greater after a nap than after wakefulness.
Associative plasticity was indexed by TMS-induced MEPs following paired associative stimulation (PAS).
PAS combines peripheral nerve stimulation with TMS to induce LTP-like plasticity in the motor cortex.
A greater increase in MEP amplitude in response to PAS was observed after the nap session compared to the wake session.
This indicates that a short nap restores the brain's capacity for Hebbian-type synaptic strengthening, which is thought to be occluded by high net synaptic strength during prolonged wakefulness.
Results
The study demonstrates that even a short nap of approximately one hour is sufficient to promote restorative effects on both homeostatic and associative synaptic plasticity.
The nap session lasted from 1:15 to 2:15 pm, corresponding to approximately one hour of opportunity for sleep.
Previous research had established nighttime sleep as the primary period for synaptic renormalization; this study extends those findings to daytime naps.
Both independent measures of plasticity (homeostatic and associative) showed consistent nap-related changes, strengthening the convergent validity of the findings.
The study used a within-subjects repeated measures design, with each participant completing both nap and wake conditions, controlling for individual differences.
Methods
The study design employed multiple non-invasive neurophysiological measures to index distinct aspects of synaptic plasticity in the human cortex.
Net synaptic strength (homeostatic plasticity) was indexed by two measures: TMS-probed corticospinal excitability and wake EEG theta activity.
Inducibility of LTP-like plasticity (associative plasticity) was indexed by MEP changes following paired associative stimulation (PAS).
Twenty healthy adults participated in a repeated measures sleep laboratory study.
The experimental design included an adaptation session and two counterbalanced experimental sessions (nap and wake).
What This Means
This research suggests that taking a short afternoon nap — roughly one hour — is enough to reset the brain's synaptic plasticity in two important ways. First, it reduces the overall 'synaptic load' that builds up during waking hours (a process called homeostatic plasticity), meaning the brain's connections are downscaled back toward a baseline level. Second, it restores the brain's ability to form new strong connections in response to learning-related stimulation (a process called associative plasticity, similar to the cellular mechanism underlying memory formation). Both of these effects were measured using non-invasive brain stimulation and brain activity recording techniques in 20 healthy adults who completed both a nap session and a wake session in a sleep laboratory.
The significance of these findings lies in connecting short daytime sleep to the same restorative brain processes previously associated only with a full night of sleep. During prolonged wakefulness, synaptic connections across the brain gradually strengthen to the point where the brain becomes less able to efficiently encode new information. Sleep — including a brief nap — appears to reset this balance, clearing the way for further learning and memory consolidation. The study used two independent measures of synaptic load (brain stimulation intensity required to produce a muscle response, and electrical brain wave patterns) that both pointed in the same direction after the nap, lending confidence to the conclusion.
This research suggests that daytime napping may serve a genuine neurobiological function in maintaining optimal brain plasticity, not merely providing subjective relief from fatigue. The findings could have relevance for understanding the cognitive benefits of napping observed in behavioral studies, and may inform future research on sleep interventions for conditions where plasticity is disrupted, such as depression or cognitive decline. However, this was a small study in healthy adults, and further research would be needed to understand how these effects translate across different populations and nap durations.
Fehér K, Henckaerts P, Hirsch V, Bucsenez U, Kuhn M, Maier J, et al.. (2026). A nap can recalibrate homeostatic and associative synaptic plasticity in the human cortex.. NeuroImage. https://doi.org/10.1016/j.neuroimage.2026.121723