title: Signal-to-noise ratio of chemosensory event-related potentials.
abstract: OBJECTIVE
  We investigated the influence of the number of stimuli on signal-to-noise (S/N) ratio of CSERP.
  
  
  METHODS
  CSERP from 20 normosmic subjects were obtained in response to stimulation with two olfactory (H(2)S and PEA) and a trigeminal (CO(2)) stimulant. For each of these odors, 160 stimuli were delivered into the right nostril (duration 200ms, mean ISI 30s) using a constant-flow, air-dilution olfactometer. For each EEG recording site (Fz, Cz, Pz, C3, C4), peak-to-peak amplitude N1P2 and noise amplitude levels were determined. Subsequently, S/N ratios were calculated.
  
  
  RESULTS
  The S/N ratios for olfactory ERP generally improved for H(2)S and PEA. For responses to PEA, S/N ratios increased significantly up to 80 averages (S/N ratio=5.6). The number of stimuli for an optimal S/N ratio for trigeminal ERP was slightly lower, i.e. 60 averages (S/N ratio=7.9).
  
  
  CONCLUSIONS
  S/N N1P2 ratios in olfactory and trigeminal ERP significantly improve with an increasing number of responses averaged under these experimental conditions. This is mainly due to a reduction of noise level. Applying more stimuli has little additional effect on S/N ratio due to a concomitant decrease in signal amplitude.
  
  
  CONCLUSIONS
  An optimal S/N ratio is essential when recording CSERP in neurodegenerative disorders, where responses may be of low amplitude, and for medico-legal purposes.
authors.affiliation: Department of Neurology, VU University Medical Center, de Boelelaan 1117, 1081 HV Amsterdam, The Netherlands. s.boesveldt@vumc.nl
authors.forename: Sanne
authors.initials: S
authors.lastname: Boesveldt
authors.forename: Antje
authors.initials: A
authors.lastname: Haehner
authors.forename: Henk W
authors.initials: HW
authors.lastname: Berendse
authors.forename: Thomas
authors.initials: T
authors.lastname: Hummel
mesh_terms: D000293:Adolescent; D000328:Adult; D002245:Carbon Dioxide / Q000494:pharmacology; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D006862:Hydrogen Sulfide / Q000494:pharmacology; D008297:Male; D009832:Olfactory Nerve / Q000502:physiology; D009833:Olfactory Pathways / Q000187:drug effects / Q000502:physiology*; D010626:Phenylethyl Alcohol / Q000494:pharmacology; D017603:Signal Detection, Psychological / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D012903:Smell / Q000502:physiology*; D013268:Stimulation, Chemical; D014276:Trigeminal Nerve / Q000502:physiology
chemical_list: D002245:Carbon Dioxide; D010626:Phenylethyl Alcohol; D006862:Hydrogen Sulfide