Olfactory Evoked Potentials and Contingent Negative Variation Simultaneously Recorded for Diagnosis of Smell Disorders

Abstract

Objective diagnosis of olfaction can be performed by registration of cortical olfactory evoked potentials (OEP) and of contingent negative variation (CNV). The CNV is a negative voltage developing at the vertex after discrimination of one of two smells while the patient is expecting a second stimulus. By an adequate procedure, including a long time window for averaging (2.56 seconds) with appropriate filters, the two tests can be performed simultaneously in a single session of less than 10 minutes. Anosmia is determinable by both OEP and CNV, although CNV shows less variability. On the other hand, CNV requires attention and some cooperation of the patient. Parosmia is accessible by CNV only; two odor qualities presented in random order have to be distinguished. Hyposmia can also be detected; just above the discrimination threshold, CNV amplitudes tend to be large--even enhanced--whereas OEP amplitudes may still be undetectable.

Time-Frequency Analysis of Chemosensory Event-Related Potentials to Characterize the Cortical Representation of Odors in Humans

“…The stimulator opened new perspectives for exploring how the human brain processes odors, through the non-invasive recording of time-locked chemosensory event-related brain potentials (ERPs) [2], [3], [4], [5]. Until then, the use of electrophysiological techniques for the functional exploration of olfaction in humans had remained limited, mainly because of the lack of adequate methods to produce a selective, controlled and transient chemosensory stimulus [6], and the fact that pioneering studies had yielded conflicting results [7], [8], [9]. Early stimulation methods relied on the delivery of brief air puffs containing a given odorant.…”

Objektiver Riechtest mit kognitiven Potenzialen

“…Die Untersuchungen werden in einem elektrisch geschirmten, gut gelüfteten Raum durchgeführt. Ein in unserem Labor erstelltes Olfaktometer [9] liefert in beide Nasenhälften bei jedem spontanen Atembeginn einen von 4 wählbaren Duft-bzw. Wasserdampfimpulsen.…”

“…Mehrere Arbeitsgruppen [6 -8] konnten nachweisen, dass das Potenzial P300 bei der Unterscheidung olfaktorischer Reize registrierbar ist. In unserer Klinik wird die CNV (contingent negative variation) zusätzlich zum Riechtest mit OEP zur Diagnostik der Parosmie abgeleitet [9,10].…”

Clinical trial design, nasal allergen challenge models, and considerations of relevance to pediatrics, nasal polyposis, and different classes of medication

“…This is very complicated for the smell stimulus, and the corresponding equipment (olfactometer) is only available in specialized laboratories. 140,141 Simpler systems for clinical use have been developed, but their precision is difficult to assess. 142,143 Unfortunately, this is relevant for the evaluation of treatment efficacy in nasal polyposis because nasal polyps may block the passage to the olfactory area and cause elevation or absence of thresholds, whereas little is known of their influence on discrimination.…”