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 (PACO2) or O2 (PAO2) 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 Cz 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 microV (mean +/- SEM). Inhalation of 6% CO2 air during HYPO induced a positive shift of the DC potential of 280.6 +/- 62.8 microV (mean +/- SEM). The magnitude of the DC potential shifts was linearly dependent on the changes in the end-tidal PACO2 (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 PACO2 level.