Hippokratia 2005; 9(3):141-144
I Konstantinidis, Th Hummel
Smell & Taste Clinic, Otolaryngology Dpt, Carl Gustav Carus University Hospital of Dresden, Dresden, Germany
Objective: The development of olfactory screening tests for the every day clinical practice was a useful tool for the assessment of olfactory and trigeminal function. These psychophysical tests have numerous advantages in the clinical utilization, but also important limitations. Subsequently, new techniques have been developed which rely less on the subjects' cooperation. The aim of this review is to describe the methods used to record and analyze olfactory and trigeminal event-related potentials (ERPs).
Methods: Odors are applied intranasaly by means of a special device called olfactometer. Stimulus presentation and recording of stimulus-linked ????segments typically are under computer control. Different techniques for the recording of olfactory system response have been developed: 1.Electro-olfactograms (???? which are electrical potentials of the olfactory epithelium that occur in response to olfactory stimulation, collected by an electrode placed in the olfactory cleft. 2. Event-related potentials which are EEG-derived poly-phasic signals, due to the activation of cortical neurons which generate electro-magnetic fields. 3. Imaging techniques include positron emission tomography (????, functional magnetic resonance imaging (FMRI), and magnetic source imaging (MSI).
Results: ERP olfactometry allows the investigation of subjects who have difficulties to respond properly (e.g., children, or aphasic, demented, unconscious, or inexperienced patients). It is also necessary for the diagnosis of olfactory deficits for medicolegal purposes. Olfactory dysfunction is an early symptom of some neurodegenerative diseases and the development of the techniques will be useful for the early diagnosis of these disorders. Conclusion: Olfactory ERPs are a validated means which allows the investigation of early components of olfactory information with a special focus on high temporal resolution. This technique is a useful tool in the study of subtle alterations in olfactory perception, odor memory, or odor aversion.
Keywords: olfaction, trigeminal, event - related potentials, objective olfactometry