title: Visually evoked gamma responses in the human brain are enhanced during voluntary hyperventilation.
abstract: Hypocapnia induced by hyperventilation (HV) has powerful effects on neuronal excitability and synaptic transmission. We have studied the effect of hyperventilation on the phase-locked oscillatory components of the evoked responses in the human brain. We recorded visually evoked magnetoencephalographic responses before, during, and after voluntary hyperventilation to pattern-reversal checkerboard stimuli. Gamma-band (30-45 Hz) responses phase-locked to the stimuli were generated in the occipital visual cortex. A wavelet-based time-frequency analysis revealed that the gamma responses increased during HV whereas their frequency did not change significantly. A recent in vitro study in the rat hippocampus demonstrated that the stability of spontaneous gamma activity increases during hypocapnia as a result of enhanced GABAergic transmission. To test if a similar mechanism could account for our findings, we performed simulations on a network of 100 Hodgkin-Huxley neurons connected by inhibitory synapses. We found that enhanced GABA(A) transmission, paired with enhanced excitability, can explain the increase in evoked gamma activity without changing the frequency.
authors.affiliation: Brain Research Unit, Helsinki University of Technology, Helsinki, FIN-02015 HUT, Finland.
authors.forename: Ole
authors.initials: O
authors.lastname: Jensen
authors.forename: Riitta
authors.initials: R
authors.lastname: Hari
authors.forename: Kai
authors.initials: K
authors.lastname: Kaila
mesh_terms: D000328:Adult; D004569:Electroencephalography; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D006985:Hyperventilation / Q000503:physiopathology*; D002534:Hypoxia, Brain / Q000503:physiopathology; D007395:Interneurons / Q000502:physiology; D008297:Male; D009433:Neural Inhibition / Q000502:physiology; D009778:Occipital Lobe / Q000503:physiopathology; D009991:Oscillometry; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation; D011963:Receptors, GABA-A / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*; D014793:Visual Cortex / Q000503:physiopathology
chemical_list: D011963:Receptors, GABA-A