Sensory evoked potentials and their changes with respiration in man and cat

Cutaneously evoked cortical potentials were recorded in man and chloralosed cats, in order to analyse the neural mechanisms responsible for their fluctuation with respiration. From the Cz region of the human scalp, 2 components of potentials, early and late, were evoked following mechanical stimulation of a finger contralateral to the recording side. These potentials varied with the phase of respiration, the late component being larger in amplitude and longer in duration when the stimulus was applied during expiration. From the surface of the primary somatosensory cortex of the cat (gyri sigmoideus posterior), 3 components of potentials were evoked following mechanical stimulation of the skin around the contralateral hind limb. These were surface negative (N1), followed by positive (P) and delayed negative (N2) potentials. The respiratory fluctuations were mainly in the duration of N2, which was shortest at the end of the inspiratory phase, while it was longest at the shifting point from expiration to inspiration. The peak time of N2 was shortest at the end of the inspiratory phase and longest at the end of the expiratory phase. On the contrary, N1 and P potentials did not fluctuate. The results indicate that the late components of cutaneously evoked cortical potentials vary, depending on the respiratory phase. Each response was increased during expiration and decreased during inspiration. These fluctuations may possibly originate in the brain stem reticular formation.