BCIwiki (bciwiki.com) — Excitability of the human motor pathway drops further during sleep spindles than in spindle-free non-rapid eye movement (NREM) sleep, but without any increase in GABA-A receptor-mediated inhibition, researchers at the Leibniz Institute for Resilience Research (LIR) and the NeuroImaging Center (NIC), Johannes Gutenberg University Medical Center, Mainz, Germany, reported in a preprint posted to bioRxiv on September 8, 2026 (DOI: 10.64898/2026.09.03.748984). The study has not been peer reviewed.
Sleep spindles are brief thalamocortical rhythms thought to support memory consolidation by opening transient windows of communication between the hippocampus and the neocortex. An earlier study using real-time electroencephalography (EEG)-triggered transcranial magnetic stimulation (TMS) found a pulsed suppression of corticospinal excitability during spindles, driven by the spindle falling phase. The team hypothesized that this suppression reflects local inhibitory network activity, measurable as short-interval intracortical inhibition (SICI) with paired-pulse TMS.
Using live EEG to time the pulses, the researchers applied single- and paired-pulse TMS over the primary motor cortex during pre-sleep wakefulness, spindle-free N2/N3 sleep, and at 4 spindle phases: peak, falling, trough and rising.
Corticospinal excitability fell sharply from wakefulness to spindle-free N2/N3 sleep and dropped further during spindles. It was numerically lowest during the falling phase and trough, but differences across phases were not statistically significant. Contrary to the hypothesis, neither spindle presence nor phase significantly changed SICI.
Secondary analyses gave preliminary evidence that slow oscillations present at the time of stimulation raised excitability and reduced SICI regardless of spindles. The authors said vigilance state, spindles and slow oscillations each contribute differently to cortical network dynamics.