Association of simultaneous sour taste stimulation with prefrontal cortex activation during stroop task performance in healthy adults: a fNIRS study.

BACKGROUND

The prefrontal cortex (PFC) plays a central role in executive functions, particularly during cognitive conflict tasks. Sour taste is a salient oral sensory stimulus and may be associated with changes in behavioral performance and prefrontal activation during cognitive tasks. This study examined whether simultaneous sour taste stimulation was associated with behavioral and prefrontal hemodynamic changes during Stroop task performance in healthy adults using functional near-infrared spectroscopy (fNIRS).

METHODS

Twenty-six right-handed healthy adults were randomly assigned to either the sour taste group (0.1 M citric acid, n = 13) or the water control group (n = 13). Participants completed a simplified color-word Stroop task in a between-subject block design while receiving simultaneous oral stimulation through cotton swabs placed on the anterior-lateral surface of the tongue. A 52-channel fNIRS system recorded changes in oxygenated and deoxygenated hemoglobin concentrations in the frontal cortex, while behavioral data (reaction time, accuracy) were collected concurrently. Behavioral data were analyzed using mixed-design analysis of variance and interference-score comparisons. Task-related Oxy-Hb responses were analyzed using a general linear model with false discovery rate correction, whereas Deoxy-Hb signals were reviewed descriptively only.

RESULTS

The sour taste group showed faster overall reaction times and higher overall accuracy than the water control group during Stroop task performance. However, no significant between-group differences were observed in Stroop interference scores for reaction time or accuracy. At the neural level, both groups showed task-related frontal activation, while the sour taste group exhibited higher Oxy-Hb β values in several channels, particularly in the left dorsolateral prefrontal cortex and frontopolar region.

CONCLUSION

Simultaneous sour taste stimulation was associated with better overall task performance and stronger task-related prefrontal hemodynamic responses in healthy adults during the Stroop task. These findings support an association between sour taste stimulation, broader behavioral facilitation, and altered prefrontal recruitment, but do not provide clear evidence for a conflict-specific enhancement of Stroop interference control.