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Background and Aim: Auditory P300 is an event-related potential. Cognitive factors like attention are involved in the generation of P300. It seems that normative variation of P300 is nec-essary for clinical purposes. Thus, the current study was designed to establish preliminary nor-mative variation of P300 amplitude and latency at Fz and Cz sites in adults. Methods: This cross-sectional study was per-formed on 20 right-handed volunteers aged 18 to 33 years. P300 was recorded monaurally with two channels at Fz and Cz placements. Two tone bursts of 1000Hz and 2000Hz were used as frequent and target stimuli, respectively. Results: The mean values of P300 amplitude and latency at Cz were 7.43±2.61 μv and 325.19±21.34 ms in the right ear and 7.38±2.73μv and 320.29±21.56 ms in the left ear, respectively. At Fz, the mean values of P300 amplitude and latency were 5.34±1.74 μv and 330.09±25.58 ms in the right ear and 5.67±2.30 μv and 329.52±29.25 ms in the left ear, respectively. The differences between the ears at Cz and Fz were not statistically sig-nificant (p˃0.05). The mean value of amplitude of P300 was sig-nificantly greater at Cz than Fz (p=0.001) alth-ough the difference in latency was not statis-tically significant between Cz and Fz (p˃0.05). Conclusion: Amplitude of P300 was greater at Cz than Fz although latency was not different. Based on these findings, amplitude and latency values can be probably used for clinical purpo-ses to assess auditory disorders. Keywords: Adult; P300; normal hearing; event related potentials
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Aud Vest Res (2017);26(2):112-116.
http://avr.tums.ac.ir
BRIEF REPORT
Preliminary normative variation of auditory P300 parameters in
adult individuals
Sirvan Najafi1, Masoumeh Rouzbahani1*, Fatemeh Heidari2, Agha Fatemeh Hosseini3
1- Department of Audiology, School of Rehabilitation Sciences, Iran University of Medical Sciences, Tehran, Iran
2- Department of Audiology, School of Rehabilitation, Shahid Beheshti University of Medical Sciences, Tehran, Iran
3- Department of Biostatistics, School of Public Health, Iran University of Medical Sciences, Tehran, Iran
Received: 3 Jan 2017, Revised: 30 Jan 2017, Accepted: 30 Jan 2017, Published: 15 Apr 2017
Abstract
Background and Aim: Auditory P300 is an
event-related potential. Cognitive factors like
attention are involved in the generation of P300.
It seems that normative variation of P300 is nec-
essary for clinical purposes. Thus, the current
study was designed to establish preliminary nor-
mative variation of P300 amplitude and latency
at Fz and Cz sites in adults.
Methods: This cross-sectional study was per-
formed on 20 right-handed volunteers aged 18
to 33 years. P300 was recorded monaurally with
two channels at Fz and Cz placements. Two
tone bursts of 1000Hz and 2000Hz were used as
frequent and target stimuli, respectively.
Results: The mean values of P300 amplitude
and latency at Cz were 7.43±2.61 µv and
325.19±21.34 ms in the right ear and
7.38±2.73µv and 320.29±21.56 ms in the left
ear, respectively. At Fz, the mean values of
P300 amplitude and latency were 5.34±1.74 µv
and 330.09±25.58 ms in the right ear and
5.67±2.30 µv and 329.52±29.25 ms in the left
ear, respectively. The differences between the
ears at Cz and Fz were not statistically sig-
nificant (p˃0.05).
The mean value of amplitude of P300 was sig-
nificantly greater at Cz than Fz (p=0.001) alth-
ough the difference in latency was not statis-
tically significant between Cz and Fz (p˃0.05).
Conclusion: Amplitude of P300 was greater at
Cz than Fz although latency was not different.
Based on these findings, amplitude and latency
values can be probably used for clinical purpo-
ses to assess auditory disorders.
Keywords: Adult; P300; normal hearing; event
related potentials
Introduction
Auditory evoked potentials (AEPs) are electrical
brain waves originated from auditory system
that would be evoked by acoustical stimulation
[1].
Event-related potentials (ERPs) are used to ass-
ess cortical region and also evaluate high-order
cognitive processes. One of the most popular
ERPs is Auditory P300 response [2]. Auditory
P300 was first introduced in 1960s by Sutton et
al. [3].
Cognitive factors such as attention are involved
in the generation of this endogenous response
[2].
Two tone burst stimuli are presented through
oddball paradigm. They are composed of stan-
dard stimuli with more probability and lower
frequency and target stimuli with lower pro-
bability and higher frequency. If a person is
* Corresponding author: Department of Audiology,
School of Rehabilitation Sciences, Iran University of
Medical Sciences, Shahid Shahnazari St., Madar
Square, Mirdamad Blvd., Tehran, 15459-13487, Iran.
Tel: 009821-22228051,
E-mail: rouzbahani.m@iums.ac.ir
113 Normative variation of P300 in adult individuals
Aud Vest Res (2017);26(2):112-116. http://avr.tums.ac.ir
focused on target stimuli through, for example,
trying to count it, then P3b is possible to be
recorded. Often, P3b is referred as P300 [4].
Various factors are involved in the generation of
P300 including auditory discrimination, tempo-
ral processing, attention, and memory [5]. P300
is a useful tool for evaluating the effectiveness
of medical, surgical, and even rehabilitation
interventions in different groups (like Alzheimer
patients, etc.) [6]. The exact origin of P300 is
unknown, but it seems that anterior cingulate
sulcus, frontal cortex, superior parietal cortex,
inferior parietal cortex, and hippocampus may
be involved [7]. Suitable and reliable placement
of non-inverting electrodes for recording P300
is midline of head that includes Fz, Cz, and Pz
[4,8,9].
From the view of age effects on P300, Stein-
schneider et al. concluded that P300 is not mat-
ure in children; by increasing age from chil-
dhood to adult, amplitude of P300 increased and
latency decreased. Also, they pointed that P300
became mature in age range of 14-16 years [10].
In contrast, most studies showed that P300 is
not affected by gender [11,12].
One of the major drawbacks of P300 is the lack
of normative data that has been accepted gene-
rally. This may be one of the reasons for not
extensive entry of P300 to the area of clinical
field. In neurological disorders, usually P300
amplitude decreases and latency increases; thus,
the aim of this study was to establish prelimi-
nary normative variation of P300 amplitude and
latency parameters in normal hearing adults
aged 18-33 years at Fz and Cz electrode pla-
cements. It is hoped that a better understanding
will be achieved on the possibility of cortical
regions involvement in different disorders by
evaluating the obtained results in this study and
comparing them with those of other disorders
and pathologies.
Methods
This cross-sectional study was performed on 20
normal hearing individuals (15 male and 5 fem-
ale) aged 18-33 years with mean and standard
deviation of 24.25±4.65 at department of Audio-
logy at School of Rehabilitation Sciences, Iran
University of Medical Sciences (IUMS). To
meet ethical consideration, the study was appro-
ved by the Ethics committee of Iran University
of Medical Sciences with code number of
IR.IUMS.REC 1395.9311301008. Also, all of
the participants signed a written informed con-
sent.
Inclusion criteria were: absence of any abnor-
mality in external and middle ear, having nor-
mal hearing threshold (25 dBHL or better at
250-8000 Hz), being right-handed, having dip-
loma degree or higher, not being in the mens-
trual cycle (for females), and lack of drow-
siness. In order to reduce variability, partici-
pants’ assessment was conducted in the mor-
ning. Case history and Edinburgh inventory
were completed for all the participants. Then,
otoscopy for examination of external auditory
canal and tympanic membrane (RiesterTM), PTA
with Hughson Westlake method (GSI audio-
meter, USA), typanometry and acousitic reflex
(Madsen, Zodiac 901, GN Otometrics, Den-
mark) were employed. If the person was eligible
for the inclusion criteria, then P300 would be
performed.
An explanation for the test was given to all the
subjects and if desired, the process of data coll-
ection was started. The participants could leave
whenever they were unwilling to continue the
study. P300 was administered with two channel
Bio-logic Navigator® Pro (Natus Company,
USA).
Lowering the impedance would result in better
and reliable recording. Therefore, the spots of
the skin where the electrodes were going to be
placed were first cleaned. Then, non-inverting
(+) electrodes were placed at Fz and Cz, inver-
ting () electrodes at M1 and M2 (that were
connected to each other through jumper lead),
and ground electrode at Fpz. Stimuli were
presented monaurally while the impedance of
the electrode was 5 kΩ or less. Also, inter-
electrode impedance difference did not exceed
2 kΩ [4]. The rate of stimulation was 0.7. Two
tone bursts of 1000 Hz (as standard stimuli
with occurrence probability of 80%) and 2000
Hz (as target stimuli with occurrence probability
of 20%) were used. The participants were
S. Najafi et al. 114
http://avr.tums.ac.ir Aud Vest Res (2017);26(2):112-116.
instructed to count only target stimuli in their
mind [4].
To increase the validity of the test, the stimuli
were first presented on a trial basis. Moreover,
to enhance the reliability using the test-retest
method, P300 was carried out in two trials. To
remove artifacts caused by blinking eye move-
ment, which would result in invalid responses
and increased test time, the participants were
instructed to open their eyes and focus on a dot
in front of them.
For data analysis, we used IBM SPSS 21. First,
the data were analyzed with Kolmogorov-
Smirnov test. The result showed that variables
had normal distribution. Paired t-test then was
used to analyze the data. p<0.05 was considered
statistically significant.
Results
A sample of P300 used in this study is shown
in Fig.1. Table 1 indicates that at Cz placement,
the mean value of P300 amplitude was
7.43±2.61 µv in the right ear and 7.38±2.73 µv
in the left ear; analysis showed that the diff-
erence was not significant (p>0.05). Also, the
mean values of P300 latency in the right and left
ears were 325.19±21.34 ms and 320.29±21.56
ms, respectively. This implied that latency was
Fz
C
z
Cz
Fz
Fig. 1. A sample of P300 response recorded.
115 Normative variation of P300 in adult individuals
Aud Vest Res (2017);26(2):112-116. http://avr.tums.ac.ir
higher in the right ear although the difference
was not significant (p>0.05).
At Fz placement, according to Table 1, the
mean value of P300 amplitude was 5.34±1.74
µv in the right ear and 5.67±2.30 µv in the
left ear. At this placement, the mean values
of P300 latency were 330.09±25.58 ms and
329.52±29.25 ms in the right and left ears, res-
pectively. However, the difference between the
ears at Fz was not significant (p>0.05).
The mean value of P300 amplitude in the right
ear was greater at Cz than Fz, which showed a
significant difference (p<0.001). Also, the mean
value of latency at Cz was lower than that of Fz
although the difference was not significant
(p>0.05).
In the left ear, the mean value of amplitude was
greater at Cz than Fz, which showed a signi-
ficant difference (p=0.001). In this ear, the mean
value of latency at Cz was lower than that of Fz
although no significant difference was observed.
Discussion
In the present study, we normalized the para-
meters of P300 such as amplitude and latency
responses in normal hearing adults using Cz and
Fz placements.
The ranges for amplitude (2-12 µv) and latency
(270-372 ms) parameters of P300 were consis-
tent with those of previous studies, for example,
conducted by Steinschneider et al. [10], Polich
et al. [11], Durret et al. [12], Fritzo et al. [13],
Massa et al. [14], and Bennington and Polich
[15], that reported the range of 2-22 µv for
amplitude and 250-400 ms for latency.
In this study, there was no significant difference
in latency between right and left ear. This
finding is consistent with those of Fritzo et al.
[13] and Massa et al. [14]. Kimura believed that
there is some asymmetry between the two hemi-
spheres in terms of verbal and non-verbal infor-
mation processing, so that the right hemisphere
is outstanding in non-verbal information (e.g.
tone burst) than the left hemisphere [16]. As we
know, left ear crosses to the left hemisphere;
therefore, we expect to observe increasing amp-
litude and decreasing latency in obtained data
from left ear [15]. However, in this study there
was no significant difference between the two
ears. Small sample size may be a reason for this
observation. Our results are also in contrast to
the findings of Li et al. [17].
Although P300 amplitude was larger at Cz
than Fz, no significant difference was observed.
These findings are consistent with those of
Wronka et al. [7], Durate et al. [12], Frrizo et al.
[13], Massa et al. [14], Bennington and Polich
[15], and Polich [18]. It may be due to the
placement of Cz electrode that was closer to the
source of P300 production. These results are in
agreement with the findings of many studies.
Considering that latency was shorter at Cz than
Fz (but with no significant difference), this
finding was in contrast to the findings of some
researchers such as Bennington and Polich [15],
and Mertens and Polich [19], who believed that
Table 1. P300 amplitude and latency in Cz and Fz placement by right and left ears of
tinnitus (n=20)
Right ear
Left ear
Mean (SD)
Min
Max
Mean (SD)
Min
Max
p
Amplitude (µV)
7.43 (2.61)
3.2
11.64
7.38 (2.73)
3.17
12.66
0.89
Latency (ms)
325.19 (21.34)
283.03
366.10
320.29 (21.56)
277.09
361.61
0.37
Amplitude (µV)
5.34 (1.74)
3.05
9.85
5.67 (2.30)
3.03
11.91
0.51
Latency (ms)
330.09 (25.58)
280.16
372.34
329.52 (29.25)
270.84
372.14
0.94
S. Najafi et al. 116
http://avr.tums.ac.ir Aud Vest Res (2017);26(2):112-116.
latency is shorter at Fz than Cz. One probable
reason may be that first, their study was con-
ducted to assess passive P3 components (P3a)
whereas this study investigated P300 (P3b) and
second, Cz was closer to the P300 response sou-
rce than Fz. However, no significant difference
in this regard may be due to the low number of
samples.
Normalized amplitude and latency parameters
found in this study can be used as cortical ele-
ctrophysiological tools to evaluate high-level
cognitive skills in neurological disorders (e.g.
central auditory processing disorder), as well as
in monitoring the treatment process and deter-
mining the effectiveness of rehabilitation prog-
rams such as auditory training.
Among the strengths of this study is the uniform
distribution of the samples in terms of age, right
handedness, and normal hearing. But in terms of
weakness of the study, it can be mentioned to
the low sample size and number of electrode
placements. Therefore, we recommend resear-
chers utilize more placement points and larger
sample sizes in future studies.
Conclusion
According to the obtained results in this study,
there was no significant difference in latency
and amplitude of P300 between right and left
ear. Also, probably due to being closer to the
P300 response source, amplitude was signifi-
cantly larger at Cz than Fz, while latency was
shorter at Cz than Fz although the latter diff-
erence was not significant.
Acknowledgments
This paper is emerged from S Najafi MSc.
dissertation in Audiology submitted in Iran
University of Medical Sciences, Tehran, Iran.
Special thanks to the all of the participants in
this study.
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