Advanced gustometer design for reliable recording of gustatory event-related potentials in healthy young adults

Abstract

Introduction: This study introduces an advanced gustometer to record Gustatory Event-Related Potentials (GERPs) in healthy young adults. We aimed to validate its functionality and reliability.

Methods: The gustometer includes a programmable controller, a human-machine interface, a modular pump system, and supporting hardware. The Neuro-Audio EEG platform recorded EEG data from 46 volunteers. Psychophysical gustatory tests assessed gustatory function. GERPs were tested using distilled water as a control and sodium chloride solutions (0.3 and 0.6%) as tastants. Tetracaine anesthetized the tongue surface to observe waveform changes and confirm GERP specificity. GERP responses were recorded at the Fz and Cz sites, focusing on the latency and amplitude of GERP P1 and P2 waves and their correlation with psychophysical test results. No stable waveforms were recorded with distilled water.

Results: All subjects displayed stable GERP waveforms following salty stimulation. These waveforms disappeared post-anesthesia, confirming GERP specificity. The recorded GERP comprised P1-N1-P2 components. The latency of P1 and P2 waves decreased with increasing salt concentration (p < .05). No significant differences in latency were observed between the Fz and Cz sites. Additionally, 48% of subjects showed increased P1-N1 and P2-N2 amplitudes with higher salty stimulation. The latency of P1 and P2 positively correlated with psychophysical test results.

Discussion: This novel gustometer effectively evoked reliable GERP waveforms. The study validated the consistency of GERP amplitude and latency with psychophysical tests, highlighting the gustometer's potential for clinical and research applications in gustatory system.

Keywords: gustatory event-related potentials; gustometer; psychophysical tests; salty stimulation; taste.

Figure 1

Photographs of the gustometer, showing its front (A) and back (B) views.

Figure 2

Schematic illustration of the gustometer. The front and back of the gustometer machine consists of a system of computer (A) controlled pumps (channel 1–3 for tastants, channel 4 for distilled water). The tastant solutions are contained in glass bottles (B); GERPs was recorded via Neuro-Audio EEG system (C); During testing, visual stimuli and auditory stimuli, as well as swallowing movements, were avoided. (D) The pump’s drive pulse is a pulsatile flush with a delay of approximately 1–5 ms, and the maximum pump flow rate is 0.85 mL/s.

Figure 3

(A) The upper image shows a side view and the lower image a front view of the mouthpiece, indicating the position where it is held between the teeth. The distance between the teeth contact point and the U point is adjustable to 1.5 ± 0.5 cm, allowing for precise positioning of the internal Teflon tubing. This ensures that the taste solution stimulates the lateral anterior part of the tongue—innervated by the facial nerve—without activating the trigeminal nerve. (B) The session timeline illustrates that each stimulus consists of four phases: preparation, taste stimulus delivery, tasting, and rinsing. Each session includes a total of 17 stimuli (sweeps). (C) The gustometer’s human-machine interface is displayed, showing parameter settings that allow for independent adjustments of each of the four channels. The stimulation calibration screen enables adjustments to the flow rate parameters.

Figure 4

(A) schematic drawing of ERP peaks and EEG recording position. (B,C) show typical recordings from 2 subjects (No 45, 38 respectively) for all experimental conditions plus the corresponding Grand Means. GERP at recording position Fz and Cz in response to distilled water (blue), 0.3% (green) and 0.6% NaCl (red) from an individual subject. Under water stimulation, no GERPs were recorded at Fz and Cz. Compared with lower salty concentration, GERP evoked by higher salty concentration at both two recording sites had larger P1-N1 and P2-N2 amplitude (B,C) and shorter P1 and P2 latency. After the subjects’ anterior tongues were sprayed with 1% tetracaine to anesthetize the areas innervated by the trigeminal and facial nerves on the tongue surface, the GERPs were tested again using the NaCl stimulus, and the aforementioned waveforms disappeared (B, purple).

Figure 5

Topographical and concentration distribution of GERPs latency (a,b) and amplitude (c,d). (F: Fz; C: Cz; 0.3: 0.3% NaCl; 0.6: 0.6% NaCl).

Figure 6

Analysis of the correlation between various GERP components and taste psychophysical tests. The latency of P1 (a,b) and P2 (c) are positively correlated with taste psychophysical tests. (F: Fz; C: Cz; 0.3: 0.3% NaCl; 0.6: 0.6% NaCl).