Summary
GABAergic intracortical inhibition in the motor cortex follows a circadian pattern, being highest in the morning and progressively declining through the day, independent of prior sleep history. This suggests that neuroplasticity and cortical excitability vary predictably across the day, with implications for timing of cognitive tasks, therapeutic interventions, and lighting strategies that support circadian alignment.
Key Findings
- Long-interval intracortical inhibition (LICI) and cortical silent periods progressively decreased over the course of the day in 15 healthy subjects measured by TMS.
- Morning cortical inhibition persisted regardless of prior sleep or sleep deprivation, confirming a circadian (not homeostatic sleep) mechanism.
- CRH infusion in the evening elevated cortisol to morning levels but did not restore morning-level GABAergic inhibition.
- Suppression of endogenous CRH release via 24-hour oral dexamethasone prevented morning inhibition, implicating the CRH/cortisol axis in circadian cortical modulation.
- Motor thresholds, short-interval intracortical inhibition/facilitation, and input/output curves showed no significant time-of-day variation.
Categories
Sleep & Circadian Health: Demonstrates circadian modulation of cortical excitability independent of sleep, linking GABAergic inhibition to time-of-day cycles.
The Science of Light: Provides neurobiological evidence for circadian-driven changes in brain physiology relevant to understanding light's role in entraining daily rhythms.
Author(s)
J Ly
Publication Year
2015
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The Science of Light
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