Abstract
ObjectivesThe objective of the present study was to investigate the usefulness of time-frequency analysis (TFA) of olfactory-induced EEG change with a low-cost, portable olfactometer in the clinical investigation of smell function.Materials & methodsA total of 78 volunteers participated. The study was composed of three parts where olfactory stimuli were presented using a custom-built olfactometer. Part I was designed to optimize the stimulus as well as the recording conditions. In part II EEG-power changes after olfactory/trigeminal stimulation were compared between healthy participants and patients with olfactory impairment. In Part III the test-retest reliability of the method was evaluated in healthy subjects.ResultsPart I indicated that the most effective paradigm for stimulus presentation was cued stimulus, with an interstimulus interval of 18-20s at a stimulus duration of 1000ms with each stimulus quality presented 60 times in blocks of 20 stimuli each. In Part II we found that central processing of olfactory stimuli analyzed by TFA differed significantly between healthy controls and patients even when controlling for age. It was possible to reliably distinguish patients with olfactory impairment from healthy individuals at a high degree of accuracy (healthy controls vs anosmic patients: sensitivity 75%; specificity 89%). In addition we could show a good test-retest reliability of TFA of chemosensory induced EEG-power changes in Part III.ConclusionsCentral processing of olfactory stimuli analyzed by TFA reliably distinguishes patients with olfactory impairment from healthy individuals at a high degree of accuracy. Importantly this can be achieved with a simple olfactometer.
Highlights
Research in the field of olfaction has focused on physiological evaluations using standard smell tests such as UPSIT and “Sniffin’ Sticks” while evaluating trigeminal functionality with menthol lateralization tests [1,2,3]
In Part II we found that central processing of olfactory stimuli analyzed by time-frequency analysis (TFA) differed significantly between healthy controls and patients even when controlling for age
Central processing of olfactory stimuli analyzed by TFA reliably distinguishes patients with olfactory impairment from healthy individuals at a high degree of accuracy
Summary
Research in the field of olfaction has focused on physiological evaluations using standard smell tests such as UPSIT and “Sniffin’ Sticks” while evaluating trigeminal functionality with menthol lateralization tests [1,2,3] These procedures are fast, reliable and can segregate individuals into groups of differencing chemosensory abilities. The temporal information of the same processes has been investigated, non-invasively with event-related potentials (ERP) [4]. This type of measurement became possible after the introduction of appropriate olfactory stimulus delivery devices that reduced somatosensory responses and provided chemosensory stimuli in a precise, timely matter [5]. Using across-trial averaging in the time-domain ERP can be characterized as a negative wave peaking approximately 320–500 ms after stimulus onset (N1), followed by a positive wave peaking approximately 450–800 ms after stimulus onset (P2 and/or P3) [6]
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