291
Electroencephalography and clinical Neurophysiology, 1991, 78:291-296 © 1991 Elsevier Scientific Publishers Ireland, Ltd. 0013-4649/91/$03.50 ADONIS 001346499100082Q
EEG 89652
BAEP amplitudes and amplitude ratios: relation to click polarity, rate, age and sex T. Sand Department of Neurology, University Hospital of Trondheim, Regionsykehuset, Trondheim (Norway)
(Accepted for publication: 13 July 1990)
Summary BAEP amplitudes and amplitude ratios in 47 healthy subjects aged 4-58 years have been investigated with respect to the simultaneous influence o~ stimulus polarity, rate, sex and age. The sex effect (larger amplitudes in women than in men) seemed to be most pronounced for wave IV-V amplitude, while the age effects (decreasing amplitudes with age) seem to be largest for the early waves. The amplitude reductions which followed an increment in the stimulus rate from 10 to 50 Hz were generally larger than the reduction following a change in the stimulus polarity from R to C clicks. The rate-induced amplitude reductions depend on click polarity for waves II and V. Thus, adaptation may be different in C click responding neurons as compared to R click responding neurons. The IV-V/I and IV-V/III amplitude ratios were both independent of sex, but the IV-V/I ratio increased significantly with age. Polarity and rate effects depended on age (wave III) but not on sex. Thus, aging may involve alterations of neural function, while the sex-related amplitude differences may be explained by non-neural factors. Key words: Evoked potentials; (Auditory); (Sex); (Age); (Polarity); (Adaptation)
Larger brain-stem auditory evoked potential (BAEP) amplitudes have generally been f o u n d in female as c o m p a r e d to male subjects (Kj~er 1980; Michalewski et al. 1980; E m e r s o n et al. 1982; C h u 1985), and amplitudes tend to decrease with age (Kja~r 1980; R o b i n s o n and Rudge 1980; Psatta and Matei 1988). Thus, amplitude variability (Rowe 1978; C h i a p p a et al. 1979) will be reduced if age and sex are considered when the " n o r m a l range" is computed. The influence of click rate u p o n B A E P amplitudes has been well studied (Jewett and Williston 1971; T h o r n t o n and C o l e m a n 1975; Pratt and Sohmer 1976; H y d e 1976; Scott and Harkins 1978; C h i a p p a et al. 1979), and most authors agree that rarefaction (R) clicks produce larger wave I amplitudes than condensation (C) clicks (Stockard et al. 1979; M a u r e r et al. 1980; Kevanishvili and A p h o n c h e n k o 1981; R u t h et al. 1982; Emerson et al. 1982; Salt and T h o r n t o n 1984; Tietze and Pantev 1986; C h a n et al. 1988). A study of polarity vs. age interactions or polarity vs. rate interactions for rates faster than 10 H z has, to our knowledge, not previously been published for B A E P amplitudes. It seems to be appropriate to investigate these interactions because the use of b o t h stimulus polarities (Emerson et al. 1982; Maurer 1985; T a c k m a n
Forty-seven control subjects (25 females and 22 males; m e a n age 29.3 years, range: 4 - 5 8 years), with no hearing complaints, were investigated. C and R click BAEPs were recorded with a 10 H z stimulation rate f r o m b o t h ears in 46 subjects and f r o m one ear in one subject. I n 39 of the subjects (22 females and 17 men; m e a n age 30.2 years, range: 7 - 5 8 years), 50 H z stimulation was also applied with C and R dicks. The subjects were split into a " y o u n g e r g r o u p " (n = 22, mean age = 18.9 years, range 4 - 2 3 years) and an "older g r o u p " (n = 25, m e a n age = 38.4 years, range 2 4 - 5 8 years). A square pulse of 0.1 msec duration drove a M a d s e n M S H 77 piezoelectric h e a d p h o n e (Sand and Sulg 1984). The stimulus intensity was 75 dB n H L 1, and two replications, each of 2000 sweeps, were made. The contralateral ear was masked with white noise (50 dB nHL). Bipolar records between the ipsilateral earlobe and vertex were obtained. A filter b a n d p a s s of 2 0 0 - 2 0 0 0
Correspondence to: Trond Sand, Regionsykehuset, Nevrologisk Avdeling~ N7006 Trondheim (Norway).
i The stimulus intensity used in two previous investigations (Sand and Sulg 1984; Sand 1986) was 75 dB nHL, not 75 dB SPL as we inadvertently had written.
and Vogel 1987) and the m e t h o d of increased stimulus rate (Pratt et al. 1981; Jacobsen et al. 1987) m a y enhance the diagnostic value of BAEPs in patients.
Subjects and methods
292
T. S A N D
TABLE 1 B A E P a m p l i t u d e s in control subjects: relation to click p o l a r i t y and rate. 1
II
III
V
IV-V
C 10Hz Mean Reference limits
516 80-1240
352 30-940
374 60-900
44zl 140- 890
519 2 4 0 - 890
R 10 Hz Mean Reference limits
583 110-1 330
266 2-850
381 60-910
54t~ 160- 1 120
597 230-1 110
C 50 Hz Mean Reference limits
327 7 0 - 720
158 20-390
247 100-400
506 220
890
512 2 4 0 - 860
R 50 Hz Mean Reference limits
434 8 0 - 990
167 10-490
276 80-570
487 1 8 0 - 920
512 2 0 0 - 940
C: condensation, R: rarefaction. U n t r a n s f o r m e d m e a n values in nanovolts. The reference l i m i t s were c o m p u t e d after s q u a r e root t r a n s f o r m a t i o n ( _+2.5 S.D.). Males a n d females have been p o o l e d (n = 47, age r a n g e 4 - 5 8 years).
Hz ( - 3 dB roll-off at 6 dB/octave) was used. Vertexpositive peaks were numbered from I to V and the following negative peaks as In to Vn (Jewett and Williston 1971). Amplitudes were measured with a ruler from the paper outprint to the nearest 12.5 nV (25 nV/mm). Peak-to-peak amplitudes were measured from the vertex-positive peaks to the following vertex-negative peaks, and peak-to-base amplitudes were measured from the positive peak to a straight line between preceding and following negative peaks. Wave I V - V amplitude was measured from the vertex-positive maximum of the I V - V complex to wave Vn. Three amplitude ratios and one "shape ratio" were analyzed: rl = I V - V / I , r2 = I V - V / I I I , r3 = I V - V / (I + II + I I I + IV - V), and the "shape ratio" SR I V - V = I V - V / ( 1 0 x d). The " d " is the interpeak latency (IPL) I I I n - V n in msec, and the amplitudes are in nanovolts. Peak-to-peak amplitudes were applied in rl, peak-to-base amplitudes in r2, square-root of peak-tobase amplitudes in r3, and square-root of the peak-topeak I V - V amplitude was used in SR IV-V. The SR
IV-V variable decreases either when amplitude decreases or when the width of the base of wave I V - V (i.e., IPL I I I n - V n ) increases. It may thus reflect the degree of neural synchronization in the upper pontine and midbrain auditory pathways. Statistical methods Statistical analysis was performed on transformed (normalized) amplitudes and ratios. Amplitudes and SR I V - V were square-root transformed, rl and r2 were natural logarithmic transformed, and r3 was inverse square root transformed. Peak-to-peak amplitudes for waves I, V and IV-V, and peak-to-base amplitudes for waves II and III were analyzed statistically after transformation. The reference limits were first computed for transformed variables (the transformed mean + 2.5 S.D.s) and inversely transformed back to the original scale. Multifactor analysis of variance and 2-tailed Student's t tests (paired or unpaired) were used to evaluate the differences between males and females, and between younger and older age groups. Mean values from right and left ears were used in the analysis of variance.
T A B L E II Multifactor analysis of variance: B A E P a m p l i t u d e s vs. polarity, rate, age a n d sex ( F ratios are tabulated). Factors
I
Click polarity Click rate Age group Sex
9.9 35.1 32.7 12.8
II
Polarity x rate Polarity × age R a t e × age
1.0 0.7 3.2
** *** *** ***
5.7 47.6 17.0 10.7
* *** *** ***
4.9 * 1.9 1.5
III
V
IV-V
0.8 34.9 * * * 11.8 * * * 17.0 * * *
5.3 * 0.0 5.6 * 31.0 * * *
4.5 5.8 4.3 36.0
7.9 * * 2.0 t .9
3.5 0.1 2.0
0.4 5.1 * 4.2 *
* * * ***
Square-root t r a n s f o r m e d a m p l i t u d e s ( m e a n value of right a n d left ear) were a n a l y z e d in 47 subjects. Significant interactions involving the sex factor were not found. * P
Electroencephalography and clinical Neurophysiology, 1991, 78:291-296 © 1991 Elsevier Scientific Publishers Ireland, Ltd. 0013-4649/91/$03.50 ADONIS 001346499100082Q
EEG 89652
BAEP amplitudes and amplitude ratios: relation to click polarity, rate, age and sex T. Sand Department of Neurology, University Hospital of Trondheim, Regionsykehuset, Trondheim (Norway)
(Accepted for publication: 13 July 1990)
Summary BAEP amplitudes and amplitude ratios in 47 healthy subjects aged 4-58 years have been investigated with respect to the simultaneous influence o~ stimulus polarity, rate, sex and age. The sex effect (larger amplitudes in women than in men) seemed to be most pronounced for wave IV-V amplitude, while the age effects (decreasing amplitudes with age) seem to be largest for the early waves. The amplitude reductions which followed an increment in the stimulus rate from 10 to 50 Hz were generally larger than the reduction following a change in the stimulus polarity from R to C clicks. The rate-induced amplitude reductions depend on click polarity for waves II and V. Thus, adaptation may be different in C click responding neurons as compared to R click responding neurons. The IV-V/I and IV-V/III amplitude ratios were both independent of sex, but the IV-V/I ratio increased significantly with age. Polarity and rate effects depended on age (wave III) but not on sex. Thus, aging may involve alterations of neural function, while the sex-related amplitude differences may be explained by non-neural factors. Key words: Evoked potentials; (Auditory); (Sex); (Age); (Polarity); (Adaptation)
Larger brain-stem auditory evoked potential (BAEP) amplitudes have generally been f o u n d in female as c o m p a r e d to male subjects (Kj~er 1980; Michalewski et al. 1980; E m e r s o n et al. 1982; C h u 1985), and amplitudes tend to decrease with age (Kja~r 1980; R o b i n s o n and Rudge 1980; Psatta and Matei 1988). Thus, amplitude variability (Rowe 1978; C h i a p p a et al. 1979) will be reduced if age and sex are considered when the " n o r m a l range" is computed. The influence of click rate u p o n B A E P amplitudes has been well studied (Jewett and Williston 1971; T h o r n t o n and C o l e m a n 1975; Pratt and Sohmer 1976; H y d e 1976; Scott and Harkins 1978; C h i a p p a et al. 1979), and most authors agree that rarefaction (R) clicks produce larger wave I amplitudes than condensation (C) clicks (Stockard et al. 1979; M a u r e r et al. 1980; Kevanishvili and A p h o n c h e n k o 1981; R u t h et al. 1982; Emerson et al. 1982; Salt and T h o r n t o n 1984; Tietze and Pantev 1986; C h a n et al. 1988). A study of polarity vs. age interactions or polarity vs. rate interactions for rates faster than 10 H z has, to our knowledge, not previously been published for B A E P amplitudes. It seems to be appropriate to investigate these interactions because the use of b o t h stimulus polarities (Emerson et al. 1982; Maurer 1985; T a c k m a n
Forty-seven control subjects (25 females and 22 males; m e a n age 29.3 years, range: 4 - 5 8 years), with no hearing complaints, were investigated. C and R click BAEPs were recorded with a 10 H z stimulation rate f r o m b o t h ears in 46 subjects and f r o m one ear in one subject. I n 39 of the subjects (22 females and 17 men; m e a n age 30.2 years, range: 7 - 5 8 years), 50 H z stimulation was also applied with C and R dicks. The subjects were split into a " y o u n g e r g r o u p " (n = 22, mean age = 18.9 years, range 4 - 2 3 years) and an "older g r o u p " (n = 25, m e a n age = 38.4 years, range 2 4 - 5 8 years). A square pulse of 0.1 msec duration drove a M a d s e n M S H 77 piezoelectric h e a d p h o n e (Sand and Sulg 1984). The stimulus intensity was 75 dB n H L 1, and two replications, each of 2000 sweeps, were made. The contralateral ear was masked with white noise (50 dB nHL). Bipolar records between the ipsilateral earlobe and vertex were obtained. A filter b a n d p a s s of 2 0 0 - 2 0 0 0
Correspondence to: Trond Sand, Regionsykehuset, Nevrologisk Avdeling~ N7006 Trondheim (Norway).
i The stimulus intensity used in two previous investigations (Sand and Sulg 1984; Sand 1986) was 75 dB nHL, not 75 dB SPL as we inadvertently had written.
and Vogel 1987) and the m e t h o d of increased stimulus rate (Pratt et al. 1981; Jacobsen et al. 1987) m a y enhance the diagnostic value of BAEPs in patients.
Subjects and methods
292
T. S A N D
TABLE 1 B A E P a m p l i t u d e s in control subjects: relation to click p o l a r i t y and rate. 1
II
III
V
IV-V
C 10Hz Mean Reference limits
516 80-1240
352 30-940
374 60-900
44zl 140- 890
519 2 4 0 - 890
R 10 Hz Mean Reference limits
583 110-1 330
266 2-850
381 60-910
54t~ 160- 1 120
597 230-1 110
C 50 Hz Mean Reference limits
327 7 0 - 720
158 20-390
247 100-400
506 220
890
512 2 4 0 - 860
R 50 Hz Mean Reference limits
434 8 0 - 990
167 10-490
276 80-570
487 1 8 0 - 920
512 2 0 0 - 940
C: condensation, R: rarefaction. U n t r a n s f o r m e d m e a n values in nanovolts. The reference l i m i t s were c o m p u t e d after s q u a r e root t r a n s f o r m a t i o n ( _+2.5 S.D.). Males a n d females have been p o o l e d (n = 47, age r a n g e 4 - 5 8 years).
Hz ( - 3 dB roll-off at 6 dB/octave) was used. Vertexpositive peaks were numbered from I to V and the following negative peaks as In to Vn (Jewett and Williston 1971). Amplitudes were measured with a ruler from the paper outprint to the nearest 12.5 nV (25 nV/mm). Peak-to-peak amplitudes were measured from the vertex-positive peaks to the following vertex-negative peaks, and peak-to-base amplitudes were measured from the positive peak to a straight line between preceding and following negative peaks. Wave I V - V amplitude was measured from the vertex-positive maximum of the I V - V complex to wave Vn. Three amplitude ratios and one "shape ratio" were analyzed: rl = I V - V / I , r2 = I V - V / I I I , r3 = I V - V / (I + II + I I I + IV - V), and the "shape ratio" SR I V - V = I V - V / ( 1 0 x d). The " d " is the interpeak latency (IPL) I I I n - V n in msec, and the amplitudes are in nanovolts. Peak-to-peak amplitudes were applied in rl, peak-to-base amplitudes in r2, square-root of peak-tobase amplitudes in r3, and square-root of the peak-topeak I V - V amplitude was used in SR IV-V. The SR
IV-V variable decreases either when amplitude decreases or when the width of the base of wave I V - V (i.e., IPL I I I n - V n ) increases. It may thus reflect the degree of neural synchronization in the upper pontine and midbrain auditory pathways. Statistical methods Statistical analysis was performed on transformed (normalized) amplitudes and ratios. Amplitudes and SR I V - V were square-root transformed, rl and r2 were natural logarithmic transformed, and r3 was inverse square root transformed. Peak-to-peak amplitudes for waves I, V and IV-V, and peak-to-base amplitudes for waves II and III were analyzed statistically after transformation. The reference limits were first computed for transformed variables (the transformed mean + 2.5 S.D.s) and inversely transformed back to the original scale. Multifactor analysis of variance and 2-tailed Student's t tests (paired or unpaired) were used to evaluate the differences between males and females, and between younger and older age groups. Mean values from right and left ears were used in the analysis of variance.
T A B L E II Multifactor analysis of variance: B A E P a m p l i t u d e s vs. polarity, rate, age a n d sex ( F ratios are tabulated). Factors
I
Click polarity Click rate Age group Sex
9.9 35.1 32.7 12.8
II
Polarity x rate Polarity × age R a t e × age
1.0 0.7 3.2
** *** *** ***
5.7 47.6 17.0 10.7
* *** *** ***
4.9 * 1.9 1.5
III
V
IV-V
0.8 34.9 * * * 11.8 * * * 17.0 * * *
5.3 * 0.0 5.6 * 31.0 * * *
4.5 5.8 4.3 36.0
7.9 * * 2.0 t .9
3.5 0.1 2.0
0.4 5.1 * 4.2 *
* * * ***
Square-root t r a n s f o r m e d a m p l i t u d e s ( m e a n value of right a n d left ear) were a n a l y z e d in 47 subjects. Significant interactions involving the sex factor were not found. * P
