Objectives: To date the temporal resolution of the detection of almost simultaneously applied intranasal trigeminal stimuli is unknown. The aim of our study was to examine this temporal resolution in an/hyposmic subjects, who are known to have reduced trigeminal sensitivity and compare it with healthy controls. Methods: Participants were 20 posttraumatic an/hyposmic patients, and 23 healthy controls (matched with regard to sex and age). Olfactory function was tested psychophysically using the Sniffin' Sticks test battery. Bilateral trigeminal stimulation was carried out using a birhinal high-precision olfactometer. The trigeminal stimulus used was CO2 60% v/v, the interstimulus interval ranged from 28 to 32 s, stimulus duration was 200 ms. Time-lags tested between right and left side of stimulation were at 40, 80, 120, 160 and 200 ms. Subjects raised their left or right hand to indicate the side on which the stimulus had been perceived first. Results: In both groups the accuracy in the trigeminal lateralization task increased with the time-lag but normosmic subjects significantly outperformed an/hyposmics in the 200 ms time-lag condition. Normosmics significantly exceeded 50% chance level at the time-lag of 80 ms, whereas an/hyposmics were only able to score above chance starting from 120 ms time-lag. Lateralization scores significantly decreased with age. Conclusions: At a time lag of 200 ms intranasal trigeminal stimuli can be lateralized. The reduced trigeminal sensitivity in patients with anosmia or hyposmia leads to an increased time lag required for correct perception of intranasal, almost simultaneously, applied stimuli.
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