Olfactory deficits decrease the time resolution for trigeminal lateralization

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 32s, stimulus duration was 200ms. Time-lags tested between right and left side of stimulation were at 40, 80, 120, 160 and 200ms. 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 200ms time-lag condition. Normosmics significantly exceeded 50% chance level at the time-lag of 80ms, whereas an/hyposmics were only able to score above chance starting from 120ms time-lag. Lateralization scores significantly decreased with age.

CONCLUSIONS

At a time lag of 200ms 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.

The depth of the olfactory sulcus is an indicator of congenital anosmia

BACKGROUND AND PURPOSE

In congenital anosmia, the OB and OT can be aplastic or hypoplastic. In clinical routine, these are sometimes difficult to assess. We thus wanted to investigate morphologic differences of the OS in patients with IA since birth or early childhood in comparison with controls, to investigate whether there is a depth of OS that is predictive of IA.

MATERIALS AND METHODS

Within the context of a 2-center study, we investigated 36 patients with IA in comparison with 70 controls. MR imaging was performed with a standard quadrature head coil (1.5T; T1- and T2-weighted spin-echo sequences were used on the coronal plane). We assessed the depth of OS in the PPTE.

RESULTS

Looking at the depth of the OS in the PPTE, we found that patients with IA had a significantly smaller OS compared with controls (P < .001). None of the healthy controls exhibited a depth of <8 mm. In patients with IA, 10 had an OS deeper than 8 mm, while 26 had an OS smaller than 8 mm. Thus, a depth of the OS less than 8 mm clearly indicates IA, with a specificity of 1 and a sensitivity of 0.72.

CONCLUSIONS

In IA, the depth of the OS in the PPTE is a useful clinical indicator. Indeed, if it is ≤8 mm, it clearly indicates IA, with a specificity of 1.