RELATION OF OLFACTORY EVENT-RELATED POTENTIALS TO CHANGES IN STIMULUSCONCENTRATION

Objective: The aim of this study was to investigate the influence of o dorant concentration on the olfactory event-related potential (OERP). Methods: OERP were evaluated in 8 men and 8 women (17-34 years of age) in response to 4 concentrations of vanillin (7, 28, 56 and 84% v/v). Sixteen presentations of each concentration (stimulus duration 200 ms, interval 40 s, flow 8 l/min) were applied in a randomized order. EEG recordings were made at 3 midline sites (pos. Fz, Ct, Pt). Amplitudes and latencies of four peaks were measured (latencies in ms at Pz after stimulation with 84% v/v vanillin): P1 (277), N1 (348), P2 (412) and P3 (496). Statistical analysis was performed with MANOVAs ('concentrat ion', 'recording site' = within-subject-factors; 'age' as covariate). Results: With increasing stimulus concentration amplitudes became sign ificantly larger; this was most pronounced for P3 (PIN1: F = 2.90, P < 0.05; N1P2: F = 5.15, P < 0.01; N1P3: F = 35.7, P < 0.001; P3: F = 38 .6; p < 0.001). Correspondingly, latencies shortened with increasing c oncentrations (P1: F = 25.2; N1:7.51; P2: 14.8; P3: 13.4; all P < 0.00 1). While there was no correlation between OERP amplitudes and butanol odor detection thresholds, latencies were the shorter the lower the s ubjects' thresholds (coefficients of correlations for peak latencies a t Cz for 84% v/v: P1 r(15) = -0.59; N1 r(15) = -0.58; P2 r(15) = -0.55 ; P-3 r(15) = -0.45). Conclusions: The results indicated that both OER P amplitudes and latencies are related to the concentration of olfacto ry stimuli. They also suggested that latencies exhibit a stronger rela tion to changes in stimulus intensity compared to OERP amplitudes. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.