Excitability of human motor and visual cortex before, during, and after hyperventilation

Area of Science:

• Neuroscience
• Human Physiology
• Cortical Excitability

Background:

• Hyperventilation (HV) affects systemic physiology and neuronal function.
• Mechanisms of HV's cortical effects remain unclear.
• Understanding HV's impact on brain excitability is crucial for clinical insights.

Purpose of the Study:

• Investigate HV-induced hypocapnia effects on primary motor (M1) and visual cortex (V1) excitability.
• Assess modulation of intrinsic neuronal circuits in the motor cortex.
• Elucidate HV's impact on measures like motor threshold (MT) and phosphene threshold (PT).

Main Methods:

• Utilized transcranial magnetic stimulation (TMS) with motor threshold (MT) and phosphene threshold (PT) measurements.
• Employed stimulus-response (S-R) curves to assess cortical excitability.
• Applied paired-pulse TMS to probe intracortical inhibition and facilitation in M1.

Main Results:

• HV significantly increased motor-evoked potential (MEP) amplitudes, especially at lower TMS intensities.
• HV reduced intracortical inhibition (ICI) without altering intracortical facilitation.
• Decreased PT and enhanced phosphene perception indicated comparable HV effects on M1 and V1 excitability.

Conclusions:

• Low PCO2 levels during HV modulate intrinsic neuronal circuits, particularly GABAergic-mediated ICI.
• HV-induced changes in MT likely involve alterations in Na+ channel conductances.
• HV impacts M1 and V1 excitability similarly, suggesting broader central nervous system modulation.