Related Experiment Video
Updated: Jun 4, 2026

Optogenetic Entrainment of Hippocampal Theta Oscillations in Behaving Mice
Published on: June 29, 2018
Circadian modulation of GABA-mediated cortical inhibition
Nicolas Lang1, Holger Rothkegel, Heidi Reiber
1Department of Neurology, Christian-Albrechts-University, 24105 Kiel, Germany. n.lang@neurologie.uni-kiel.de
Abstract:
Circadian rhythms exert powerful influence on various aspects of human physiology and behavior. Here, we tested changes of human cerebral cortex excitability over the course of the day with transcranial magnetic stimulation (TMS). At different times of the day, intracortical and corticospinal excitability of the primary motor cortex (M1) was evaluated in 15 healthy subjects by TMS of left M1. While motor thresholds, short-interval intracortical inhibition and facilitation and input/output curves remained unchanged, we found that a specific form of γ-aminobutyric acid (GABA)-mediated intracortical inhibition, revealed by long-interval intracortical inhibition and cortical silent periods, progressively decreased during the course of the day. Additional experiments demonstrated that morning inhibition persisted irrespective of previous sleep or sleep deprivation. Corticotropin-releasing hormone (CRH) infusions in the evening lead to morning cortisol levels but did not restore levels of morning inhibition, whereas suppression of endogenous CRH release by repeated oral dexamethasone intake over 24 h prevented morning inhibition. The findings suggest a specific modulation of GABAergic motor cortex inhibition within the circadian cycle, possibly linked to the CRH system, and may indicate a neurobiological basis for variable neuroplasticity over the course of the day.
More Related Videos
Related Concept Videos
Antiepileptic Drugs: GABAergic Pathway Potentiators
The key GABA pathway potentiators used in epilepsy management are as follows.
Benzodiazepines are a well-known class of drugs used for their...
Circadian Rhythms and Gene Regulation
Circadian Rhythms and Gene Regulation
Ligand-Gated Ion Channel Receptor: Gating Mechanism
CNS Depressants: Barbiturates and Benzodiazepines
Chronopharmacokinetics: Circadian Rhythms and Influence on Drug Response
The time of drug administration is an important factor to consider, as it can influence the toxic dose of a drug. For example, a study conducted by Prins et al. in 1997 examined the effects of the timing of...

