Neuroscience Letters 406 (2006) 222–226 Chemosensory event-related potentials during sleep—A pilot study Boris A. Stuck a , Heike Weitz b , Karl H ¨ ormann a , Joachim T. Maurer a , Thomas Hummel b,∗ a Department of Otorhinolaryngology, Head and Neck Surgery, University Hospital Mannheim, Germany b Smell & Taste Clinic, Department of Otorhinolaryngology, University of Dresden Medical School (“Technische Universit¨ at Dresden”), Fetscherstrasse 74, 01307 Dresden, Germany Received 1 July 2006; received in revised form 26 July 2006; accepted 26 July 2006 Abstract Aim of the present pilot study was to investigate whether cortically generated chemosensory event-related potentials (ERPs) can be recorded during sleep. Chemosensory function during sleep was assessed in 14 healthy female volunteers. An overnight polysomnography was performed to assess nocturnal sleep and to classify sleep stages. Chemosensory ERPs were recorded using air-dilution olfactometry. H 2 S (4 ppm) was used for olfactory and CO 2 (40%, v/v) for trigeminal stimulation. Chemosensory ERPs could be recorded during sleep for both olfactory and trigeminal stimuli in some but not all subjects. Compared to baseline, latencies of olfactory ERPs were longer and amplitudes were larger during light sleep and slow wave sleep (SWS). For trigeminal stimulation N1 latencies were longest during REM sleep. These results indicate that both trigeminal and olfactory ERPs can be recorded during sleep suggesting that chemosensory stimuli are processed on a cortical level during sleep. © 2006 Elsevier Ireland Ltd. All rights reserved. Keywords: Chemosensation; Event related potentials; Olfaction; Trigeminal Sensory activation during sleep has been studied extensively for visual, auditory, and somatosensory stimuli. In terms of electro- physiological measures, it was shown that the late components of auditory event-related potentials (ERPs) are significantly altered during sleep, while brainstem auditory evoked poten- tials were relatively unaffected [3]. During both slow wave sleep (SWS) and REM-sleep responses exhibited longer latencies while reports for amplitudes were equivocal [7,18,22,23]. How- ever, more recent research suggests that amplitude N1 decreases while P2 actually increases [4,6]. No such data exists for olfac- tory ERPs. Research suggests that olfactory stimuli are processed during sleep as awakening reactions occur [2,5]. In this context, how- ever, it is not exactly clear whether these responses are due to activation of the trigeminal system which is also stimulated by most odors [8]. Further, olfactory information is processed dif- ferently than other sensory information [10]. Aims of the present pilot study were to investigate chemosensory ERPs during sleep to assess (1) whether chemosensory ERPs can be recorded dur- ing sleep, also with regard to arousal reactions/awakenings and a good signal-to-noise ratio, and, if so, (2) whether sleep does ∗ Corresponding author. Tel.: +49 351 458 4189; fax: +49 351 458 4326. E-mail address: thummel@rcs.urz.tu-dresden.de (T. Hummel). alter chemosensory ERPs in the same way as it alters ERPs in other sensory modalities. The study was conducted at the Department of Otorhino- laryngolgoy, Head and Neck Surgery Mannheim. The study protocol was approved by the local ethics board of the Faculty of Clinical Medicine Mannheim of the University of Heidelberg; written informed consent was obtained from all participating subjects. Participants: 15 young healthy female volunteers were included in this prospective study (mean age 24.6 ± 1.9 years, range: 21–29 years). Exclusion criteria were present/previous history of smell or taste disorders, use of any medication known to affect chemosensory function [1], and a history of sleep dis- orders. At the screening visit, relevant nasal pathology such as mucosal inflammation, significant septal deviation, or nasal polyposis were ruled out with a clinical examination including nasal endoscopy. Patency of the nasal airways was also ascer- tained using active anterior rhinomanometry (Rhinomanometer 300, ATMOS Medizintechnik GmbH & Co.KG, Lenzkirch, Ger- many). Psychophysical testing of olfactory function: All of the partic- ipating subjects underwent olfactory testing using the “Sniffin’ Sticks” test kit to establish normal olfactory function [12,14]. Testing involved assessment of butanol odor thresholds, odor discrimination, and odor identification. 0304-3940/$ – see front matter © 2006 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2006.07.068