Electroencephalography and clinical Neurophysiology, 84 (1992) 84-89 © 1992 Elsevier Scientific Publishers Ireland, Ltd. 0168-5597/92/$05.00
84
EVOPOT 90675
Differences in h u m a n evoked potentials related to olfactory or trigeminal chemosensory activation Thomas Hummel and Gerd Kobal Department ~]"Pharmacology and Toxicolo,t,% Unit'ersity of Erlangen-Niirnberg, D-8520 Erlangen (F. R. G. ) (Accepted for publication: 12 July 1991)
Summary The aim of the present study was to determine, whether there are differences in the topographical distribution of chemosensory evoked potentials (CSEPs) due to stimulation with different odorous substances. The odorants used in the study which mainly excited the olfactory nerve were vanillin and acetaldehyde; those which additionally excited the trigeminal nerve were sulphur dioxide and ammonia. Twelve subjects participated in the study. The subjects separately estimated the intensity of the odorous and of the painful/pricking sensation caused by the stimuli, and described the odorous qualities in their own words. CSEPs were recorded from 7 positions. After stimulation with "olfactory" substances maximum CSEP amplitudes were recorded at parieto-central sites, and after stimulation with "trigeminal" substances maximum amplitudes were obtained at the vertex, Following stimulation with ammonia and sulphur dioxide amplitudes were largest contralatera[ to the stimulated nostril. In contrast, little difference in CSEP amplitudes was observed between hemispheres after stimulation with vanfllin or acetaldehyde. Thus, the topographical distribution of CSEP amplitudes may provide information with regard to the sensory system (olfactory or trigeminal) activated by the presentation of an odorous stimulus. Key words: Olfactory nerve; Trigeminal nerve; Laterality; Smell; Pain; Cortical generator; Topographical distribution
Two sensory systems participate in the perception of an odorant - - the olfactory and the somatosensory systems. Since scientists first became interested in the sense of smell, the question of the degree to which an odorant excites either the one or the other has remained an unsolved problem. By investigating patients whose olfactory nerves have been severed by trauma or intracranial surgery it can be determined whether a certain odorant selectively excites filaments of the olfactory nerve (Furukawa et al. 1988; Hendriks 1988), e.g., such anosmic patients were able to perceive carbon dioxide, but were unable to smell an odorant such as vanillin (Kobal and Hummel 1991). Kobal et al. (1989)demonstrated in healthy subjects that they inevitably failed to localize the stimulated side after randomized, dichorhinic chemical stimulation of the nasal mucosa with vanillin and hydrogen sulphide, whereas they effortlessly succeeded in doing so after stimulation with carbon dioxide and menthol. From this phenomenon the authors deduced that to be
Correspondence to: Dr. Thomas Hummel, Department of Pharmacology and Toxicology, University of Erlangen-Nflrnberg, Universit~itsstr. 22, D-8520 Erlangen (F.R.G.). Tel.: 09131/852277; Fax: 09131/206119.
unlocatable is a characteristic feature of odorous substances which mainly excite the olfactory nerve. Another approach to differentiate between olfactory and trigeminal activity is to determine the differences in the shape of chemosensory evoked potentials (CSEPs) after stimulation with different odorous stimulants. However, Kobal and Hummel C. (1988)were not able to find a distinctive, discriminative feature in the pattern of the evoked potentials after stimulation with either painful non-odorous carbon dioxide or vanillin, which mainly excites the olfactory nerve, Since they only recorded CSEPs from one position (Cz/A1), it was not possible to determine whether there are topographical differences in the distribution of CSEPs in relation to the activation of either the olfactory or the trigeminal system. Thus, the aim of the present study was to investigate differences in the topographical distributions of CSEPs after stimulation with two separate odorant pairs, designed to excite the trigeminal and the olfactory system to different degrees. For stimulation of the trigeminal nerve two substances, sulphur dioxide and ammonia, were chosen. These are easily locatable, evoke painful in addition to odorous sensations, and can be detected by anosmics (Elsberg et al. 1935; Eccles 1982). Vanillin and acet-
85
OLFACTORY AND TRIGEMINAL CHEMOSENSORY EPs aldehyde were selected for stimulation of the olfactory nerve. In preliminary experiments it was found that neither could be localized in a dichorhinic stimulation paradigm. The conclusion that both odorants in the given concentrations excited only the olfactory nerve was supported by the observation that neither could be detected by anosmic patients (Kobal and Hummel 1991).
into the left nostril (stimulus duration 200 msec; interstimulus interval approximately 40 sec).
Chemosensory evoked potentials
Four odorants were investigated: vanillin (Sigma; 0.78 ppm), acetaldehyde (Fluka; 800 ppm), ammonia (Linde; 457 ppm) and sulphur dioxide (Linde; 137 ppm). The cristalline vanillin and the liquid acetaldehyde were diluted with propylene glycol (Fluka), the gaseous stimulants ammonia and sulphur dioxide were taken from pressure cylinders.
CSEPs were recorded with an 8-channel E E G amplifier (Mingograf E E G 10, Siemens), from 7 positions of the 10/20 system referred to A1. Possible blink artifacts were registered from F p 2 / A 1 . The bandpass of the system was between 0.2 and 70 Hz, and the sampling frequency of the stimulus-linked E E G segments of 2048 msec was 250 Hz. Recording started 240 msec before stimulus onset. After analogue-to-digital conversion, the E E G segments were stored on disk cartridges of a computer ( P D P l l / 2 3 , DEC). Subsequently, the averaged records were evaluated off-line (Kobal and Hummel 1989). All single responses contaminated by eye blinks or eye movements were discarded from the average, and averaged responses with a blink artifact greater than 40 /xV in the Fp2 lead ( F p 2 / A 1 ) were excluded from further analysis. Due to the stimulation procedure 16 records were available for averaging in order to produce late nearfield evoked potentials. The peak-to-peak amplitudes N 1 / P 2 , and the latencies of N1 and P2 (in relation to the stimulus onset) were measured (Kobal and Hummel C. 1988). In addition, the base-to-peak amplitudes N1 and P2 were evaluated.
Test procedure
Qualitative evaluation of the odorants
Subjects were comfortably installed in an electrically shielded chamber with good air circulation. The presentation of the stimuli did not activate mechano- or thermosensors in the nasal mucosa due to a specially devised stimulation technique (for details see Kobal 1985; Kobal and Hummel C. 1988). White noise of approximately 50 dB SPL prevented the subjects from hearing the switching process. The subjects participated in 4 testing sessions on 4 different days. A preliminary testing session was conducted so that the subjects could familiarize themselves with the experimental conditions. In this session the subjects also practiced a specific breathing technique (velopharyngeal closure: Kobal and Hummel 1989) in order to avoid respiratory flow of air inside the nasal cavity during stimulation. Two measuring sequences with an interval of approximately 30 rain constituted the single testing session. Technical limitations of the stimulation device demanded the following procedures: if vanillin had been randomly selected to be presented in the first sequence of a testing session, acetaldehyde was presented in the second, and vice versa. In contrast, ammonia and sulphur dioxide were presented in both sequences of the respective testing session. During one measuring sequence 16 chemical stimuli were delivered
After each testing sequence the subjects were required to describe the quality of the perceived odorants. They were at liberty to choose their own descriptors.
Material and methods
Twelve healthy volunteers (6 females, 6 males; between 23 and 34 years of age, mean age 27.3 years) participated in the study. They were informed about the aim of the experiment and had given written consent. The study was performed in accordance with the Declaration of H e i s i n k i / T o k y o / V e n i c e .
Odorants
Intensity estimates At the end of a measuring sequence the subjects estimated, with the aid of two visual analogue scales, (1) the intensity of the odorous sensation, and (2) the intensity of the painful/pricking sensation. Scale graduations numbered from 1 to 7. The gradation mark 7 was defined as "very strong smell" or "very painful/pricking," the mark 1 was defined as "very weak smell" or "very weak painful/pricking sensation."
Tracking performance During the measuring sequences two squares of different sizes appeared on the video screen (Kobal et al. 1990). Subjects were instructed to keep the smaller square, which could be controlled by a joy-stick, inside the larger one, which moved unpredictably. This task was evaluated in arbitrary units. If subjects never lost track of the larger square, the result was 100 units, if they never succeded in keeping the smaller square inside the larger one, the result was 0 units.
86
T. HUMMEL, G. KOBAL ChemosensoryEvokedPotentials(Pos.Cz)
Statistical analys& B e f o r e b e i n g s u b m i t t e d to statistical analysis, t h e raw d a t a o b t a i n e d in b o t h m e a s u r i n g s e q u e n c e s w e r e a v e r a g e d s e p a r a t e l y for e a c h o d o r a n t . S u b s e q u e n t l y , the m e a n s of b o t h m e a s u r i n g s e q u e n c e s w e r e e v a l u a t e d as follows. (a) E s t i m a t e s of o d o r o u s a n d stinging s e n s a t i o n s as well as units of the t r a c k i n g p e r f o r m a n c e w e r e submitt e d to analysis of v a r i a n c e ( M A N O V A , r e p e a t e d m e a s u r e m e n t design, with " o d o r a n t " as w i t h i n - s u b j e c t factor; d f 3 3 / 3 ) . (b) T o find d i f f e r e n c e s b e t w e e n r e c o r d s f r o m different sites C S E P p a r a m e t e r s w e r e i n v e s t i g a t e d by m e a n s of a 2-way M A N O V A ( r e p e a t e d m e a s u r e m e n t s design) with w i t h i n - s u b j e c t factors " o d o u r " a n d " r e c o r d i n g p o s i t i o n " . B e f o r e this analysis d a t a u n d e r w e n t a norm a l i z a t i o n p r o c e d u r e , as p r o p o s e d by M c C a r t h y a n d W o o d (1985), to avoid m i s i n t e r p r e t a t i o n , i.e., t h e m e a n m i n i m u m a n d m a x i m u m v a l u e s w e r e f o u n d at the 7 r e c o r d i n g sites for e a c h c o n d i t i o n (i.e., o d o r a n t a n d C S E P p a r a m e t e r ) , s u b t r a c t e d f r o m e a c h d a t a point, a n d t h e result was d i v i d e d by t h e d i f f e r e n c e b e t w e e n mean maximum and minimum. T h e SPSS PC + p r o g r a m was u s e d for statistical analysis.
Examplesof One Subject
J
A
.
.
Grand Means
~
Acetaldehyde
,.....~J~ ~
sutphur
....
,a
FO0 [msecl ~ F0 [rnsecl Fig. l. Chemosensory evoked potentials (CSEPs): grand means averaged across all subjects (n = 12); evoked potentials of a single subject after stimulation with the 4 stimulants obtained in the 2 different sessions. CSEPs to the trigeminal stimulants sulphur dioxide and ammonia have larger amplitudes and shorter latencies compared to the responses to the olfactory stimulants vanillin and acetaldehyde.
p l i t u d e s N1 a n d P2, as well as t h e p e a k - t o - p e a k amplit u d e N1P2, o f t h e C S E P e v o k e d by a m m o n i a a n d s u l p h u r dioxide, w e r e l a r g e r t h a n t h o s e e v o k e d by a c e t a l d e h y d e a n d vanillin. L a t e n c i e s N1 a n d P2 w e r e s h o r t e s t w h e n a m m o n i a a n d s u l p h u r dioxide w e r e applied.
Topographical distribution of CSEP
Results
R e s u l t s of statistical analyses a r e given in T a b l e I.
Chemosensory evoked potentials G r a n d m e a n s o f c h e m o s e n s o r y e v o k e d p o t e n t i a l s , as well as e x a m p l e s f r o m o n e subject, a r e given in Figs. 1 a n d 2. T h e g r a p h s show clearly t h a t b a s e - t o - p e a k am-
TABLE I Results of statistical analysis. (A) Ratings, tracking performance: MANOVA (repeated measurement design, within-subject factor "odour" [dr 33/3]) Tracking performance Odorous sensation Pricking sensation
F = 0.73 F = 9.24 F = 13.37
n.s. P < 0.001 P < 0.001
It was possible to g r o u p the C S E P s into two categories (Fig. 3). W h e n a c e t a l d e h y d e a n d vanillin were used as stimulants, a m p l i t u d e s w e r e largest at p a r i e t o c e n t r a l r e c o r d i n g sites. In contrast, with s u l p h u r dioxide a n d a m m o n i a as stimulants, a m p l i t u d e s o b t a i n e d at Cz w e r e l a r g e r t h a n t h o s e at any o t h e r r e c o r d i n g position. A d d i t i o n a l l y , d i f f e r e n c e s b e t w e e n C S E P amp l i t u d e s r e c o r d e d ipsi- a n d c o n t r a l a t e r a l to t h e stimul a t e d side w e r e s m a l l e r a f t e r p r e s e n t a t i o n of e i t h e r a c e t a l d e h y d e or vanillin t h a n t h o s e o b t a i n e d after stimulation with s u l p h u r dioxide a n d a m m o n i a . T h e s e findTopographicalDistributionof CSEP: GrandMeans(n=12) Stimulus:SulphurDioxide
Stimulus:Acetaldehyde
(B) Chemosensory evoked potentials: MANOVA (repeated measurement design, within-subject factors "odour" [df 33/3] and "recording position" [df 66/6], interaction between both factors [dr 198/18])
Amplitude N1 Amplitude P2 Amplitude NI/P2 Latency NI Latency P2
Factor odour
Factor recording position
Interaction odour x position
F = 0.30 n.s. F = 0.36 n.s.
F = 2.60 P < 0.05 F = 1.51 n.s. F = 17.98 P < 0.001 F = 1.25 n.s.
F = 0.14 n.s. F = 0.03 n.s. F = 0.57 n.s.
F=42.46P
84
EVOPOT 90675
Differences in h u m a n evoked potentials related to olfactory or trigeminal chemosensory activation Thomas Hummel and Gerd Kobal Department ~]"Pharmacology and Toxicolo,t,% Unit'ersity of Erlangen-Niirnberg, D-8520 Erlangen (F. R. G. ) (Accepted for publication: 12 July 1991)
Summary The aim of the present study was to determine, whether there are differences in the topographical distribution of chemosensory evoked potentials (CSEPs) due to stimulation with different odorous substances. The odorants used in the study which mainly excited the olfactory nerve were vanillin and acetaldehyde; those which additionally excited the trigeminal nerve were sulphur dioxide and ammonia. Twelve subjects participated in the study. The subjects separately estimated the intensity of the odorous and of the painful/pricking sensation caused by the stimuli, and described the odorous qualities in their own words. CSEPs were recorded from 7 positions. After stimulation with "olfactory" substances maximum CSEP amplitudes were recorded at parieto-central sites, and after stimulation with "trigeminal" substances maximum amplitudes were obtained at the vertex, Following stimulation with ammonia and sulphur dioxide amplitudes were largest contralatera[ to the stimulated nostril. In contrast, little difference in CSEP amplitudes was observed between hemispheres after stimulation with vanfllin or acetaldehyde. Thus, the topographical distribution of CSEP amplitudes may provide information with regard to the sensory system (olfactory or trigeminal) activated by the presentation of an odorous stimulus. Key words: Olfactory nerve; Trigeminal nerve; Laterality; Smell; Pain; Cortical generator; Topographical distribution
Two sensory systems participate in the perception of an odorant - - the olfactory and the somatosensory systems. Since scientists first became interested in the sense of smell, the question of the degree to which an odorant excites either the one or the other has remained an unsolved problem. By investigating patients whose olfactory nerves have been severed by trauma or intracranial surgery it can be determined whether a certain odorant selectively excites filaments of the olfactory nerve (Furukawa et al. 1988; Hendriks 1988), e.g., such anosmic patients were able to perceive carbon dioxide, but were unable to smell an odorant such as vanillin (Kobal and Hummel 1991). Kobal et al. (1989)demonstrated in healthy subjects that they inevitably failed to localize the stimulated side after randomized, dichorhinic chemical stimulation of the nasal mucosa with vanillin and hydrogen sulphide, whereas they effortlessly succeeded in doing so after stimulation with carbon dioxide and menthol. From this phenomenon the authors deduced that to be
Correspondence to: Dr. Thomas Hummel, Department of Pharmacology and Toxicology, University of Erlangen-Nflrnberg, Universit~itsstr. 22, D-8520 Erlangen (F.R.G.). Tel.: 09131/852277; Fax: 09131/206119.
unlocatable is a characteristic feature of odorous substances which mainly excite the olfactory nerve. Another approach to differentiate between olfactory and trigeminal activity is to determine the differences in the shape of chemosensory evoked potentials (CSEPs) after stimulation with different odorous stimulants. However, Kobal and Hummel C. (1988)were not able to find a distinctive, discriminative feature in the pattern of the evoked potentials after stimulation with either painful non-odorous carbon dioxide or vanillin, which mainly excites the olfactory nerve, Since they only recorded CSEPs from one position (Cz/A1), it was not possible to determine whether there are topographical differences in the distribution of CSEPs in relation to the activation of either the olfactory or the trigeminal system. Thus, the aim of the present study was to investigate differences in the topographical distributions of CSEPs after stimulation with two separate odorant pairs, designed to excite the trigeminal and the olfactory system to different degrees. For stimulation of the trigeminal nerve two substances, sulphur dioxide and ammonia, were chosen. These are easily locatable, evoke painful in addition to odorous sensations, and can be detected by anosmics (Elsberg et al. 1935; Eccles 1982). Vanillin and acet-
85
OLFACTORY AND TRIGEMINAL CHEMOSENSORY EPs aldehyde were selected for stimulation of the olfactory nerve. In preliminary experiments it was found that neither could be localized in a dichorhinic stimulation paradigm. The conclusion that both odorants in the given concentrations excited only the olfactory nerve was supported by the observation that neither could be detected by anosmic patients (Kobal and Hummel 1991).
into the left nostril (stimulus duration 200 msec; interstimulus interval approximately 40 sec).
Chemosensory evoked potentials
Four odorants were investigated: vanillin (Sigma; 0.78 ppm), acetaldehyde (Fluka; 800 ppm), ammonia (Linde; 457 ppm) and sulphur dioxide (Linde; 137 ppm). The cristalline vanillin and the liquid acetaldehyde were diluted with propylene glycol (Fluka), the gaseous stimulants ammonia and sulphur dioxide were taken from pressure cylinders.
CSEPs were recorded with an 8-channel E E G amplifier (Mingograf E E G 10, Siemens), from 7 positions of the 10/20 system referred to A1. Possible blink artifacts were registered from F p 2 / A 1 . The bandpass of the system was between 0.2 and 70 Hz, and the sampling frequency of the stimulus-linked E E G segments of 2048 msec was 250 Hz. Recording started 240 msec before stimulus onset. After analogue-to-digital conversion, the E E G segments were stored on disk cartridges of a computer ( P D P l l / 2 3 , DEC). Subsequently, the averaged records were evaluated off-line (Kobal and Hummel 1989). All single responses contaminated by eye blinks or eye movements were discarded from the average, and averaged responses with a blink artifact greater than 40 /xV in the Fp2 lead ( F p 2 / A 1 ) were excluded from further analysis. Due to the stimulation procedure 16 records were available for averaging in order to produce late nearfield evoked potentials. The peak-to-peak amplitudes N 1 / P 2 , and the latencies of N1 and P2 (in relation to the stimulus onset) were measured (Kobal and Hummel C. 1988). In addition, the base-to-peak amplitudes N1 and P2 were evaluated.
Test procedure
Qualitative evaluation of the odorants
Subjects were comfortably installed in an electrically shielded chamber with good air circulation. The presentation of the stimuli did not activate mechano- or thermosensors in the nasal mucosa due to a specially devised stimulation technique (for details see Kobal 1985; Kobal and Hummel C. 1988). White noise of approximately 50 dB SPL prevented the subjects from hearing the switching process. The subjects participated in 4 testing sessions on 4 different days. A preliminary testing session was conducted so that the subjects could familiarize themselves with the experimental conditions. In this session the subjects also practiced a specific breathing technique (velopharyngeal closure: Kobal and Hummel 1989) in order to avoid respiratory flow of air inside the nasal cavity during stimulation. Two measuring sequences with an interval of approximately 30 rain constituted the single testing session. Technical limitations of the stimulation device demanded the following procedures: if vanillin had been randomly selected to be presented in the first sequence of a testing session, acetaldehyde was presented in the second, and vice versa. In contrast, ammonia and sulphur dioxide were presented in both sequences of the respective testing session. During one measuring sequence 16 chemical stimuli were delivered
After each testing sequence the subjects were required to describe the quality of the perceived odorants. They were at liberty to choose their own descriptors.
Material and methods
Twelve healthy volunteers (6 females, 6 males; between 23 and 34 years of age, mean age 27.3 years) participated in the study. They were informed about the aim of the experiment and had given written consent. The study was performed in accordance with the Declaration of H e i s i n k i / T o k y o / V e n i c e .
Odorants
Intensity estimates At the end of a measuring sequence the subjects estimated, with the aid of two visual analogue scales, (1) the intensity of the odorous sensation, and (2) the intensity of the painful/pricking sensation. Scale graduations numbered from 1 to 7. The gradation mark 7 was defined as "very strong smell" or "very painful/pricking," the mark 1 was defined as "very weak smell" or "very weak painful/pricking sensation."
Tracking performance During the measuring sequences two squares of different sizes appeared on the video screen (Kobal et al. 1990). Subjects were instructed to keep the smaller square, which could be controlled by a joy-stick, inside the larger one, which moved unpredictably. This task was evaluated in arbitrary units. If subjects never lost track of the larger square, the result was 100 units, if they never succeded in keeping the smaller square inside the larger one, the result was 0 units.
86
T. HUMMEL, G. KOBAL ChemosensoryEvokedPotentials(Pos.Cz)
Statistical analys& B e f o r e b e i n g s u b m i t t e d to statistical analysis, t h e raw d a t a o b t a i n e d in b o t h m e a s u r i n g s e q u e n c e s w e r e a v e r a g e d s e p a r a t e l y for e a c h o d o r a n t . S u b s e q u e n t l y , the m e a n s of b o t h m e a s u r i n g s e q u e n c e s w e r e e v a l u a t e d as follows. (a) E s t i m a t e s of o d o r o u s a n d stinging s e n s a t i o n s as well as units of the t r a c k i n g p e r f o r m a n c e w e r e submitt e d to analysis of v a r i a n c e ( M A N O V A , r e p e a t e d m e a s u r e m e n t design, with " o d o r a n t " as w i t h i n - s u b j e c t factor; d f 3 3 / 3 ) . (b) T o find d i f f e r e n c e s b e t w e e n r e c o r d s f r o m different sites C S E P p a r a m e t e r s w e r e i n v e s t i g a t e d by m e a n s of a 2-way M A N O V A ( r e p e a t e d m e a s u r e m e n t s design) with w i t h i n - s u b j e c t factors " o d o u r " a n d " r e c o r d i n g p o s i t i o n " . B e f o r e this analysis d a t a u n d e r w e n t a norm a l i z a t i o n p r o c e d u r e , as p r o p o s e d by M c C a r t h y a n d W o o d (1985), to avoid m i s i n t e r p r e t a t i o n , i.e., t h e m e a n m i n i m u m a n d m a x i m u m v a l u e s w e r e f o u n d at the 7 r e c o r d i n g sites for e a c h c o n d i t i o n (i.e., o d o r a n t a n d C S E P p a r a m e t e r ) , s u b t r a c t e d f r o m e a c h d a t a point, a n d t h e result was d i v i d e d by t h e d i f f e r e n c e b e t w e e n mean maximum and minimum. T h e SPSS PC + p r o g r a m was u s e d for statistical analysis.
Examplesof One Subject
J
A
.
.
Grand Means
~
Acetaldehyde
,.....~J~ ~
sutphur
....
,a
FO0 [msecl ~ F0 [rnsecl Fig. l. Chemosensory evoked potentials (CSEPs): grand means averaged across all subjects (n = 12); evoked potentials of a single subject after stimulation with the 4 stimulants obtained in the 2 different sessions. CSEPs to the trigeminal stimulants sulphur dioxide and ammonia have larger amplitudes and shorter latencies compared to the responses to the olfactory stimulants vanillin and acetaldehyde.
p l i t u d e s N1 a n d P2, as well as t h e p e a k - t o - p e a k amplit u d e N1P2, o f t h e C S E P e v o k e d by a m m o n i a a n d s u l p h u r dioxide, w e r e l a r g e r t h a n t h o s e e v o k e d by a c e t a l d e h y d e a n d vanillin. L a t e n c i e s N1 a n d P2 w e r e s h o r t e s t w h e n a m m o n i a a n d s u l p h u r dioxide w e r e applied.
Topographical distribution of CSEP
Results
R e s u l t s of statistical analyses a r e given in T a b l e I.
Chemosensory evoked potentials G r a n d m e a n s o f c h e m o s e n s o r y e v o k e d p o t e n t i a l s , as well as e x a m p l e s f r o m o n e subject, a r e given in Figs. 1 a n d 2. T h e g r a p h s show clearly t h a t b a s e - t o - p e a k am-
TABLE I Results of statistical analysis. (A) Ratings, tracking performance: MANOVA (repeated measurement design, within-subject factor "odour" [dr 33/3]) Tracking performance Odorous sensation Pricking sensation
F = 0.73 F = 9.24 F = 13.37
n.s. P < 0.001 P < 0.001
It was possible to g r o u p the C S E P s into two categories (Fig. 3). W h e n a c e t a l d e h y d e a n d vanillin were used as stimulants, a m p l i t u d e s w e r e largest at p a r i e t o c e n t r a l r e c o r d i n g sites. In contrast, with s u l p h u r dioxide a n d a m m o n i a as stimulants, a m p l i t u d e s o b t a i n e d at Cz w e r e l a r g e r t h a n t h o s e at any o t h e r r e c o r d i n g position. A d d i t i o n a l l y , d i f f e r e n c e s b e t w e e n C S E P amp l i t u d e s r e c o r d e d ipsi- a n d c o n t r a l a t e r a l to t h e stimul a t e d side w e r e s m a l l e r a f t e r p r e s e n t a t i o n of e i t h e r a c e t a l d e h y d e or vanillin t h a n t h o s e o b t a i n e d after stimulation with s u l p h u r dioxide a n d a m m o n i a . T h e s e findTopographicalDistributionof CSEP: GrandMeans(n=12) Stimulus:SulphurDioxide
Stimulus:Acetaldehyde
(B) Chemosensory evoked potentials: MANOVA (repeated measurement design, within-subject factors "odour" [df 33/3] and "recording position" [df 66/6], interaction between both factors [dr 198/18])
Amplitude N1 Amplitude P2 Amplitude NI/P2 Latency NI Latency P2
Factor odour
Factor recording position
Interaction odour x position
F = 0.30 n.s. F = 0.36 n.s.
F = 2.60 P < 0.05 F = 1.51 n.s. F = 17.98 P < 0.001 F = 1.25 n.s.
F = 0.14 n.s. F = 0.03 n.s. F = 0.57 n.s.
F=42.46P
