Abstract
Contingent negative variation (CNV) was elicited using electrical taste stimulation as the warning stimulus. Stimuli were generated for 100 msec or 500 msec using a bipolar stainless steel electrode disc with the center portion acting as the anode and the outer portion as the cathode. The imperative stimulus was a pure tone of 1 kHz at 60 dB and the interstimulus interval of paired stimuli was 2000 msec. The electrode was gently held in contact with the tongue by a specially made fixture and electrical taste stimuli were presented at 5-sec intervals. The CNV was recorded in 10 normal subjects at the Cz site of the 10-20 International System, referred to linked earlobes with a forehead ground. The results from 20 presentations were averaged.
The mean threshold measured by electrogustometry employing a monopolar electrode as the anode was-4.2dB (0dB=8μA), and the mean thresholds measured with the bipolar electrode at a stimulus duration of 100 msec and 500 msec were 0dB and -1.4dB, respectively. As the mean threshold obtained with a duration of 500 msec was closer to the electrogustometry findings than that obtained with a duration of 100 msec, a stimulus duration of 500 msec was useful for determining the CNV threshold.
The CNV could be recorded in all 1O normal subjects, and the late component was conspicuous because of recording at the Cz site. In four subjects, the P300 could be recorded after the warning stimulus at an intensity of 40μA. Clear P300 waveforms were obtained after warning stimuli with a duration of 100 msec, but the P300 waveforms obtained with a stimulus duration of 500 msec were wide and the bounds of the P300 and the CNV were unclear. As it was necessary to maintain the concentration of the subjects during CNV recording, we had to shorten the test period, but we could still approximately determine the CNV thresholds corresponding to the electrogustometry thresholds.
In conclusion, it was possible to evaluate the electrical taste threshold objectively from the CNV and the P300 elicited by electrical taste stimulation.
