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Excitability of human motor cortex during hyperventilation and hypercapnia
1Playfair Neuroscience Unit, University of Toronto, Toronto Western Hospital, ON, Canada.
Canadian Journal of Physiology and Pharmacology
|August 1, 1994
Summary
Changes in carbon dioxide levels (PCO2) do not significantly affect corticospinal neuron excitability. This study found no impact on motor cortex neurons during varying PCO2 conditions in healthy subjects.
Area of Science:
- Neuroscience
- Physiology
Background:
- The excitability of corticospinal neurons is crucial for motor control.
- The influence of arterial carbon dioxide partial pressure (PCO2) on central nervous system excitability is not fully understood.
Purpose of the Study:
- To investigate whether changes in PCO2 affect the excitability of human corticospinal neurons.
- To determine the relationship between PCO2 levels and the excitability of the fast-conducting corticospinal pathway.
Main Methods:
- Transcranial magnetic stimulation was used to activate corticospinal neurons in the motor cortex.
- Excitatory postsynaptic potentials (EPSPs) in spinal motoneurons were measured indirectly via motor unit firing probability.
- Cortical neuron excitability was inferred from the amplitude of composite EPSPs under varying PCO2 conditions (normocapnia, hypocapnia, hypercapnia).
Main Results:
- No statistically significant changes in corticospinal neuron excitability were observed across different PCO2 levels.
- Mean end-tidal PCO2 values ranged from 2.9 kPa (hypocapnia) to 6.9 kPa (hypercapnia).
- Individual subject data showed no consistent trend related to PCO2 variations.
Conclusions:
- The excitability of corticospinal neurons, as assessed by magnetic stimulation, is not significantly altered by changes in PCO2.
- These findings suggest that the motor cortex's response to magnetic stimulation is robust to alterations in blood gas levels within the tested physiological range.