PALAVRAS CHAVE: potencial evocado auditivo, diferença sexual, diferença manuali dade. Behavioral and physiological hemispheric asymmetry of function ...
EFFECTS OF STIMULATION INTENSITY, GENDER A N D HANDEDNESS UPON AUDITORY EVOKED POTENTIALS
SUSANA
CAMPOSANO
* — FERNANDO
LOLAS
*
SUMMARY — Left handers and women show less anatomical brain asymmetry, larger corpus callosum and more bilateral representation of specific functions. Sensory and cognitive components of cortical auditory evoked potentials (AEF) have been shown to be asymmetric in right handed males and to be influenced by stimulus intensity. In this study the influence of sex, handedness and stimulus intensity upon AEP components is investigated under basal conditions of passive attention. 14 right handed mtales, 14 right handed females, 14 left handed males, and 14 left handed females were studied while lying awake and paying passive attention to auditory stimulation (series of 100 binaural clicks, duration 1 msec, rate 1/sec, at four intensities). Cz, C3 and C4 referenced to linked mastoids and right EOG were recorded. Analysis time was 400 msec, average evoked potentials were based on 100 clicks. Stimulus intensity and gender affect early sensory components (P1N1 and N1P2) at central leads, asymmetry is influenced only by handedness, right handers showing larger P1N1 amplitudes over the right hemisphere. KEY
WORDS: auditory evoked potential,
sex difference,
handedness
difference.
Efectos de la intensidad de la estimulación, sexo y manualidade sobre el potencial evocado auditivo. RESUMEN — Los sujetos zurdos y de sexo femenino tienden a exhibir menores grados de asimetría anatómica, mayores diámetros del cuerpo calloso y mayor representación bilateral de funciones específicas. Los componentes sensoriales y cognitivos del potencial evocado auditivo (PEA) cortical han demostrado sensibilidad a la intensidad de estimulación y asimetría en sujetos masculinos. En este estudio se investiga la influencia de sexo, manualidad e intensidad de la estimulación sobre los componentes corticales del PEA. 56 suje tos voluntarios fueron sometidos a estimulación auditiva (series de 100 clicks binaurales, duración de 1 mseg, frecuencia de 1/seg, a cuatro diferentes intensidades) instruyéndoseles a prestar atención pasiva. Se registró derivaciones Cz, C3 y C4 referidas a mastoides bila teral y electrooculograma derecho, el tiempo de análisis fue de 400 mseg, los promedios fueron obtenidos sobre 100 clicks. La intensidad de la estimulación y el sexo afectan los componentes sesoriales corticales P1N1 y N1P2 en la derivación central. La asimetría sólo es influenciada por la manualidad; los Ss diestros exhiben mayores amplitudes P1N1 en el hemisferio derecho. PALAVRAS LLAVE: nualidad. PALAVRAS
potencial
CHAVE: potencial
evocado auditivo,
diferencia
sexual,
diferencia
evocado
diferença
sexual,
diferença manuali
auditivo,
de ma
dade.
Behavioral and physiological hemispheric asymmetry of function has been related to organism variables such as sex and handedness. Left-handers and women tend to show less anatomical asymmetry 5,8,13. The corpus callosum is larger in both groups, in men at the splenium and in left handers at the central region 740,16. Early * Psychophysiology Unit, Department of Physiology and Biophysics, Faculty of Medi cine, University of Chile. This research is supported by FONDECYT Project 1126/90, and the University of Chile (D.T.I.). Dr. Fernando Lolas — Department of Physiology and Biophysics, versity of Chile - P.O. Box 70005 - Santiago 7 - Chile.
Faculty
of Medicine,
Uni
sensory components df cortical auditory potential ( A E P ) have been shown to asymmetric in right handed males and to be influenced by stimulus intensity 4 , n .
be
It is investigated in this study the influence of sex, handedness and stimulus intensity upon A E P components and their hemispheric asymmetry in basal conditions. Symmetrical (binaural) stimulation with low informational content (click) and passive attention conditions were used in order to avoid selecting a lateralized processing mode. METHODS 52 the
unpaid
volunteers
university
women
and
Edinburgh
without
community
14
left
(14
handed
I n v e n t o r y 12.
right
Concordant
hit
preference
were
included).
history
dislexia
Subjects stay
awake
binaural SPL).
not or
lying
and
clicks,
1
Intensity Recordings
1
and
were
Table
was
made
from
Biodata
1 — Amplitude
(uV)
right no
a
ball
handers
left
1/
for
it
writing, also
isolated
Stimulation at
men,
using
requested
was
were
recruited
14
right
some
items
eating
with
(Ss. who
requested
from
handed of
a
showed
not
to
the
spoon, mixed have
a
relatives.
electrically sec,
handed
assessed
was
handed
and
rate
left
was
preference
stimulation.
Cz, C3 a n d
Right PA
were
EOG
four
room
consisted
intensities
C4 referenced was
amplified
P1N1,
analysis N1P2
and
times
Averages
time
to
linked
simultaneously
20,000
400 amplifiers.
rejection; of
14
impairment
were
of
four
(63,
74,
instructed series 87
and
to
of
100
97
dB
random.
Signals
artifact
For and
duration,
hearing
men,
throwing
acoustically
in
or
Handedness manual
and
auditory
electrodes.
using
without
an to
sequence
electrodes.
100 H z
intensity,
in
msec
silver-silverchloride supraorbital
a nail,
stuttering
listen
handed
women).
h o l d i n g a h a m m e r to of
neurological
was
P2N2
and
were
400 m s e c components
mastoids
recorded band based
pass on
spanned at
CZ.
with
from
filtered
100 c l i c k s by
surface
infra
640 d a t a
and
between at
each
points.
Latency N 1 P 2 and at
the
PI,
NI,
E O G exceeded
ponents PI,
of
were
Nl,
Amplitude
C3/Ampl.
C3
Amplitude (ANOVA, being
Table
and
Balanced)
sex,
analyzed
+
using
2 —
at
for
(msec)
and
amplitude
at
deflection
N2,
150-300
proportional
LPAC)
peak
to
peak
a cursor program.
maximal
the
averages
of
are
for
intensity.
nonparametric
Latency
peak
to
performed and
to
using
was
in
the
ampliutdes the
Cz, averages
maximal
were
of
rejected.
following
time
P1N1,
excursion Com
windows:
ms.
activation
obtained
If
as
of
the
left
follows:
hemisphere
(Left
L P A O = Amplitude
at
C4.
latency was
components
100-190 m s ;
Coefficient,
Ampl.
handedness
peak P2,
coefficient
Proportional
N2
measured
according
60-120 m s ;
asymmetry at
and
were
maximal
identified
40-80 m s ; An
P2
P2N2 complexes
C3
procedures
PI,
NI,
shown
Cz
P2,
in
latencies and
C4
Tables and
amplitude
(Wilcoxon Sign
and
N2
1
and
amplitudes Rank
components
and
2.
latency
Test).
at
Analysis
and
CZ.
for
of
variance
LPAC,
differences
factors were
RESULTS A Figure 1
and
tendency 1.
was
Amplitude
of
different
less
at
in
63 d B
variance
right
Values
appreciated
by
amplitudes latency
for
for of
these
differences handed
(pC3
larger
in
women
averages
and
and
right
standard
handers
can
deviations
are
be
appreciated
shown
in
in
Tables
2.
Analysis shows
to
males
of
in F i g u r e 2.
as
right
lead
variables
factors
at
74
left
T h e r e is no
N1P2
87
found dB
C3 and by
and the
for
P2N2
peak-to-peak
components
PINT,
(pC3
shown only shown
asymmetry.
in
in
right in
in
right
Table
influenced Table
handers,
Wilcoxon:
handed
females
5. by
handedness
4.
Differences
(Table can
be
COMMENTS
Stimulus intensity and gender influence early sensory components of A E P at central leads but exert no influence on hemispheric asymmetry of electrocortical signals. Asymmetry is influenced only by handedness, with right handers showing larger amplitudes over the right hemisphere. Amplitude at central lead is influenced by the three factors studied: P1N1 by intensity; N 1 P 2 by intensity, gender and handedness; and P 2 N 2 only by handedness. The influence of intensity on early cortical components is well known, therefore they are called «stimulus d e p e n d e n t s . Sexual differences are also known, women tend to have larger amplitudes 3 . 14
The influence of handedness on central lead amplitude is a new finding and could be explained if left handers had more bilateral activation of supratemporal regions. Only right handed subjects show greater C 4 amplitudes, in left handers no significant asymmetry could be demonstrated. Amplitude depends on previous acti vation of generator sites, the greater the previous activation, the lower is the evoked amplitude ! 5 . This view would be concordant with greater left side activation in right handers (thus showing lower amplitudes at C 3 ) and with bilateral activation in left handers (thus showing less asymmetry and lower amplitudes at C z ) . This bilateral activation can be related to the thicker central part of corpus callosum, which includes auditory cortex callosal fibers 1. Anova shows asymmetry as measured by L P A C of P 1 N 1 and P 2 N 2 to be influenced only by handedness. This kind of A E P study is complementary with behavioral asymmetry studies and contributes data on early and basic aspects of hemispheric processing, which can be used for prediction of behavioral outcomes.
REFERENCES 1.
Alexander study.
2.
Bear
MD,
D,
Schiff
asymmetries. 3.
Buchsbaum evoked Collin
D,
MS,
Henkin
F.
by
Galaburda A M . Holloway
and
9.
Koff
E,
scan
hemispheric
Arch
Neurol
11.
Harshman
functions.
Lacoste-Utamsing Lolas of
1982, F,
study.
of
of
a
CT
case
analysis
of
cerebral
auditory
sex
differences
in
patients
with
gonadal
(AEP)
augmen-
of
evoked
potential
asymmetry 1985,
left-handedness.
Res
JM, in
and
averaged
37:137-144.
dimorphism
in
Neurobiol
differences
Brain
1974,
Hemispheric
Human
Sex
Pieniadz
Quantitative
observation
Bohemoslovaca
Sexual
asymmetries
1986,
pathways:
20:436-439.
E.
correlates
MC. R.
MA,
1983,
Physiologia
Programs
Naeser
Science
asymmetry
Szelag
replication
Kimura
10.
D,
Lacoste
8.
auditory
R.
Age
with
Neurophysiol
Hemispheric B,
RL.
population,
Clin
Biological
RL,
callosal
M, Freeman
Christiansen
normal
left-handers.
7.
of
43:598-603.
Psychophysiology
6.
verbal
RI,
a
Czachowska-Sieszycka
extension
Greenberg 1986,
Electroenceph
C, L o l a s
material
J,
Neurol in
Localization
38:802-804.
Saver
responses
ting-reducing. 5.
RL.
1988,
Arch
dysgenesis. 4.
Warren
Neurology
in
1984, -
1986,
processing
of
verbal
Neurol
human
1984,
corpus
4:120-125.
callosum:
an
5:87-91.
organization
for
verbal
and
non
61:428-441.
Foundas
right
Semin
the
brain
in
34:21-24.
AL,
and
Levine
HL.
left-handed
Computed
male
tomographic
and
female
subjects.
human
corpus
callosum.
43:487-491. C,
Holloway
RL.
Sexual
dimorphism
in
the
Rees
R.
216:1431-1432.
Collin
C,
Camposano
augmenting/reducing
in
S,
Btcheberrigaray
visual
and
auditory
R,
evoked
Hemispheric
potentials.
Biol
asymmetry
Psychiat
1987,
22:1413-1416. 12.
Oldfield
RC.
The
Neuropsychologia 13.
Piazza of
14.
Picton I:
15.
Evaluation W,
influence
of
SF. 1985,
of
tasks.
SA,
in
The
analysis
of
handedness:
JL, brain
and
handedness
HI,
Galambos
Electroenceph
Thomas
cognitive
229:665-668.
sex
Neuropsychologia
Krausz
components.
Shucard
and
the
Endiburgh
Inventory.
9:97-113.
nonverbal
differences
Witelson Science
The
and
T W , Hillyard
Shucard pheric
16.
DM.
verbal
assessment
1971,
DG.
connection:
R.
Clin
Auditory
processing. the
in
1980,
the
Human
Neuphysiol evoked
Science corpus
hemispheric
specialization
18:163-176. auditory 1974,
potentials
evoked
potentials.
36:179-190. as
probes
of
hemis
1977, 179:1295-1297. callosum
is
larger
in
left-handers.
