Evaluation of olfactory function by topographic EEG analysis in patients with Parkinson's disease

Olfactory function impairment has been observed in patients with idiopathic Parkinson's disease (PD) using psychophysical procedures. In this study, an electrophysiological technique based on spectral analysis and topographic EEG mapping was used to evaluate EEG arousal response to olfactory stimulation in ten normal subjects and ten PD patients in stage II according to Hoehn and Yahr's scale, all of whom had akinetic-rigid syndrome and were receiving chronic L-Dopa therapy. Olfactory function was stimulated using diluted benzaldehyde by means of an apparatus set up in our laboratory. Spontaneous and post-olfactory stimulus EEGs were recorded from 20 electrodes placed upon the scalp according to the Int. 10-20 System. Total EEG power (from 0.5 to 19.5 Hz) was evaluated over 10 sec. artefact-free epochs. An olfactory arousal reaction was detected in nine of the ten PD patients and was characterised by a significant decrease in total power similar to that observed in all of the 10 normal subjects; these variations in EEG were found in all but the anterior regions of the scalp. The use of this technique does not seem to reveal any clear alteration in the olfactory function of PD patients.