Scalp-recorded direct current potential shifts induced by hypocapnia and hypercapnia in humans

Shifts in scalp-recorded direct current (DC) potential were studied in relation to the changes in end-tidal partial CO2 (PACO(2)) or O-2 (PAO(2)) of the expired gas either during hyperventilation (HV), hypoventilation (HYPO) or inhalation of high CO2 content air during HV or HYPO in 10 healthy subjects. The DC potential was obtained through a chopper stabilized type of DC amplifier from Ct referred to linked earlobes. Each session was comprised of 3 min control, 3 min experimental and 5 min recovery periods. HV induced a negative shift of the DC potential of 765.5 +/- 203.0 mu V (mean +/- SEM). Inhalation of 6% CO2 air during HYPO induced a positive shift of the DC potential of 280.6 +/- 62.8 mu V (mean +/- SEM). The magnitude of the DC potential shifts was linearly dependent on the changes in the end-tidal PACO(2) (r = 0.78, P < 0.0001). There was no change in the cephalic inter-electrodes impedance during each experimental session. The results suggest that the scalp-recorded DC potentials reflect the changes in cortical excitability associated with the PACO(2) level.