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Original Article 

Relationship between Sympathetic Skin Responses 
and Auditory Hypersensitivity to Different 
Auditory Stimuli 



J. Phys. Ther. Sci. 
26:1087-1091,2014 



FuMi Kato, OTR, MS>)*, Ryoichiro Iwanaga, OTR, PhD^), Mami Chono, OTR^), 

Saori Fujihara^), Akiko Tokunaga, OTR, MS^^, Jun Murata, OTR, PhD'), 

Koji Tanaka, OTR, MS'', Hideyuki Nakane, MD, PhD'), Goro Tanaka, OTR, PhD« 

Department of Psychiatric Rehabilitation Sciences, Nagasaki University Graduate School of 
Biomedical Sciences: 1-7-1 Sakamoto, Nagasaki City, Nagasaki 852-8520, Japan 
Hirado City Health and Welfare Centre for Children with Disabilities, Japan 
^) NPO Peaacas, Japan 



Abstract. [Purpose] Auditory hypersensitivity has been widely reported in patients with autism spectrum disor- 
ders. However, the neurological background of auditory hypersensitivity is currently not clear The present study 
examined the relationship between sympathetic nervous system responses and auditory hypersensitivity induced 
by different types of auditory stimuli. [Methods] We exposed 20 healthy young adults to six different types of audi- 
tory stimuli. The amounts of palmar sweating resulting from the auditory stimuli were compared between groups 
with (hypersensitive) and without (non-hypersensitive) auditory hypersensitivity. [Results] Although no group x 
type of stimulus x first stimulus interaction was observed for the extent of reaction, significant type of stimulus x 
first stimulus interaction was noted for the extent of reaction. For an 80 dB-6,000 Hz stimulus, the trends for pal- 
mar sweating differed between the groups. For the first stimulus, the variance became larger in the hypersensitive 
group than in the non-hypersensitive group. [Conclusion] Subjects who regularly felt excessive reactions to auditory 
stimuli tended to have excessive sympathetic responses to repeated loud noises compared with subjects who did not 
feel excessive reactions. People with auditory hypersensitivity may be classified into several subtypes depending on 
their reaction patterns to auditory stimuli. 

Key words: Auditory hypersensitivity. Sympathetic nervous system. Auditory stimuli 

(This article was submitted Nov. 20, 2013, and was accepted Jan. 30, 2014) 



INTRODUCTION 

Sensory processing disorders have been widely reported 
in patients with Autism Spectrum Disorder (ASD)' "^l In 
particular, one sensory processing problem, auditory hy- 
persensitivity, has been observed in 23.9% to 70% of sub- 
jects with ASD^' and acuity of hearing (hyperacusis) has 
been noted in 18% to 63%^- ^\ Because auditory hypersen- 
sitivity has been reported to prevent adaptive behavior^' 
elucidation of its neurological background and creation of 
an objective index of auditory hypersensitivity would be 
helpful for treatment interventions and for devising sup- 
port methods for patients with auditory hypersensitivity. 
Although verification of the auditory processing mecha- 
nisms in ASD has been performed at various stages of 
the auditory system with electrophysiological indices, the 
neurological background has remained unclear"' Here, 



*Corresponding author. Fumi Kato (E-mail: fumik_de@ 
hotmail.com) 

©2014 The Society of Physical Therapy Science. Published by IPEC Inc. 
This is an open-access article distributed under the terms of the Cre- 
ative Commons Attribution Non-Commercial No Derivatives (by-nc- 
nd) License <http://creativecommons.Org/licenses/by-nc-nd/3.0/>. 



we identified problems in auditory processing in a clini- 
cal setting and confirmed the presence of hypersensitivity 
based on questionnaires that were completed by patients, 
guardians, therapists, or teachers. However, we did not use 
an objective index. 

In order to quantitatively evaluate the response of an 
individual to auditory stimuli, autonomic nerve reactions 
can be evaluated by measuring palmar sweating. Because 
eccrine sweat glands are induced by mental stress and are 
controlled by the cholinergic fibers of sympathetic nerves, 
measuring the amount of sweating allows for evaluation of 
sympathetic nerve activity during psychological stress'^ 
In this study, we evaluated sympathetic nerve activity by 
using palmar sweating as an index. 

In a previous study. Miller et al.'^' performed experi- 
ments on patients with Fragile X syndrome who had a 
strong hypersensitivity towards sensation by using target 
and electrodermal activity as an index. In that study, the 
sympathetic nerve response for a given stimulus was re- 
ported to be much larger and habituation was reported to 
be difficult in patients with Fragile X syndrome compared 
with those in normally developed children. Based on the 
questionnaire administered by Chang et al."' to parents of 
patients with targeted ASD, patients with auditory hyper- 



1088 J. Phys. Ther. Sci. Vol. 26, No. 7, 2014 



sensitive ASD continuously have a much stronger sympa- 
thetic nerve response to auditory stimuli compared with 
those in normally developed controls. Furthermore, Brown 
et al.'**' used a self-report questionnaire in normal adults 
and examined the relationship between sympathetic nerve 
response and a sensation evaluation questionnaire. These 
authors classified subjects as those who had or who did not 
have a hypersensitive trend and measured their skin con- 
ductance. They reported that the responses were larger and 
habituation was difficult in subjects with auditory hypersen- 
sitivity. The findings of that report suggest the possibility 
of a relationship between the auditory-hypersensitive trend 
derived from the questionnaire and the abnormal responses 
of sympathetic nerves. However, the relationship between 
the characteristics of sound (frequency, dB) and the sym- 
pathetic nerve response to sound stimulation is not clear. In 
addition, the sympathetic nerve response to high- and low- 
frequency sound stimuli may vary because of differences in 
frequencies. In order to clarify sympathetic nerve responses 
to various types and various frequencies of auditory stimu- 
li, we evaluated healthy adults, classified them into groups 
with (hypersensitive) and without (non-hypersensitive) au- 
ditory hypersensitivity using a self-report questionnaire, 
and measured the variations in palmar sweating elicited by 
sound stimuli with different characteristics. 

SUBJECTS AND METHODS 

In this study, 20 healthy volunteer students (4 males, 16 
females) ranging in age from 19 to 25 years (mean ± stan- 
dard deviation [SD], 21 ± 3 years) were recruited at Na- 
gasaki University. None of the subjects had any diseases, 
medical history, or ear problems. All experimental methods 
were explained to the subjects. After obtaining consent for 
participation, we evaluated the characteristics of auditory 
hypersensitivity with the Adolescent/Adult Sensory Profile 
(AASP)''l The AASP is a standardized and self-completed 
questionnaire used in individuals whose ages range from 11 
to 65 years. It consists of 60 items based on a 5 -point Likert 
scale, with the answers ranging from almost never (1 point) 
to almost always (5 points). Higher scores indicate atypical 
sensory processing. AASP scores are comprised of four ar- 
eas: low registration, sensation seeking, sensory sensitivity, 
and sensation avoiding. Neurologically, both hypersensitiv- 
ity (51, I startle easily from an unexpected or loud noise; 
54, 1 am distracted if there is a lot of noise around; or 60, 1 
find it difficult to work with a noisy background) and sen- 
sation avoiding (53, When others are watching TV, 1 leave 
the room or ask them to turn it off; 56, I use strategies to 
drown out sound; or 57, I stay away from noisy settings) 
represent a low threshold state for auditory stimuli. In this 
study, we calculated the total score for hypersensitivity in 
hearing and sensation avoidance (30 full points) and used it 
as an index for auditory hypersensitivity. Additionally, we 
calculated the median scores and classified the subjects into 
the hypersensitive group if their scores were greater than 
the median or the non-hypersensitive group if their scores 
were less than the median. 

Palmar sweating was recorded continuously from the 



thenar eminence using a probe attached to a 1-cm^ area 
and a sweating rate meter (SS-100, KANDS Co., Ltd., 
Aichi Prefecture, Japan). Auditory stimuli from the stimu- 
lator (MEB-5504, Neuro Pack^, Nihon Kohden Corpora- 
tion, Tokyo, Japan) were applied to both ears of the subject 
through headphones (DR-531, Nihon Kohden Corporation). 
Palmar sweating (mg/cm^/min) and auditory stimuli sig- 
nals were simultaneously recorded with a computer and 
an A/D converter (PowerLab 16/23, ADInstruments Ltd., 
Dunedin, New Zealand) with a sampling frequency of 
400 Hz. The data were analyzed with a software program 
(LabChart 6, ADInstruments Ltd.). The entire experiment 
was performed in a sound-shielded room, and the room 
temperature was 23 °C. Once all of the preparations were 
complete, each subject was requested to sit in an easy chair. 
The experiment was performed as described below. First, 
we informed the subjects that they would be hearing several 
series of sounds with different frequencies and magnitudes 
and instructed them not to move until the end of the trial, 
of which they would be informed by the experimenter in 
charge. Subsequently, each subject rested for 3 min. We en- 
sured that huge variations in thenar sweating were not ob- 
served, and we then began the trial. For each trial, we took 
a baseline measure for 30-s in the beginning. One trial was 
comprised of repeating the same tone burst five times with 
a 30-s interval between bursts. We performed six such trials 
in total. These six trials were performed with the following 
six types of tone burst stimulations: 500 Hz-20 dB, 500 Hz- 
50 dB, 500 Hz-80 dB, 6,000 Hz-20 dB, 6,000 Hz-50 dB, 
and 6,000 Hz-80 dB. Each auditory stimulus was a tone 
burst of 1,000-ms duration, with a rise and fall duration of 
10 ms. In order to counterbalance the effect of the order of 
stimulus presentation, the presentation order was random- 
ized between subjects. To measure the degree of discomfort 
for each type of stimuli, the subjects were asked to select 
one of the following descriptors for each respective stimuli 
type: extreme discomfort, uncomfortable, a little discom- 
fort, slight discomfort, or no discomfort at all. 

To analyze the palmar sweating, the data from each sub- 
ject were averaged every second. For each trial, the 0- to 
30-s data before every first round of stimulation were con- 
sidered the baseline values. Moreover, for each trial, after 
deriving the peak value of the palmar sweating from each 
baseline value, the variation was calculated for each stimu- 
lus, and this value was compared between the groups. To 
compare the reaction magnitude for each type of stimulus 
between the groups, we derived the amounts of palmar 
sweating for the baseline value and the first stimulus by 
analyzing the effect of the amount of reaction for group x 
type of stimulus x time (before vs. after the first stimulus) 
with a three-way analysis of variance (ANOVA). 

To derive the amount of palmar sweating for the frequen- 
cy of each type of stimulus for both groups, we observed the 
mutual interaction, the main effects of group, and the num- 
ber of times by performing a two-way repeated ANOVA 
with a post hoc Bonferroni t-test. To analyze the differences 
in the degrees of discomfort between the groups in each 
type of stimulus, we used Mann-Whitney U tests for each 
stimulus type. 



1089 



Table 1. Charactcrislics oflhc subjecls 





Hyper 


Non-hyper P 




(n=10) 


(n=10) 


Age (yrs) 


20.9±1.7 


20.4±1.5 


Gender (m/f) 


2/8 


2/8 


Index for auditory hypersensitivity 


17.7±3.1 


9.5±1.7 ** 


SR (mg/cm^/min) 


1.737±0.974 


1.452±0.687 



Values are mean ± SD. *p < 0.05; **p < 0.01. 

Hyper: hypersensitive group, Non-hyper: non-hypersensitive group, Index for 
auditory hypersensitivity: the total score of the items that reflected hypersensitiv- 
ity and avoidance in the Adolescent/Adult Sensory Profile auditory items, SR: 
sweating rate 



Table 2. Degree of discomfort score in both groups 





Hyper 


Non-hyper p 




(n=10) 


(n=10) 


80dB-6,000 Hz 


4.80 ±0.4 


4.4 ± 0.5 


80dB-500 Hz 


4.80 ± 0.4 


3.1 ± 1.7 ** 


50dB-6,000 Hz 


2.20 ± 1.0 


2.1 ±0.9 


50dB-500 Hz 


1.30 ±0.5 


1.2 ±0.4 


20dB-6,000 Hz 


1.78 ± 1.0 


1.7 ± 1.0 


20dB-500 Hz 


1.20 ±0.6 


1 


Values are mean ± 


SD. *p < 0.05; 


**p<0.01. 



Hyper; hypersensitive group. Non-hyper: non-hyper- 
sensitive group 




0 30 60 90 120 150 180 

Time in seconds (sec) 



Fig. 1. Responses to 80 dB-6,000 Hz auditory stimuli of a repre- 
sentative individual from the hypersensitive group. 
Each vertical line represents an auditory stimulus. 



This study adhered to the Declaration of Helsinki and 
was approved by the Ethics Committee of the Department 
of Health Sciences, Nagasaki University Graduate School 
of Biomedical Sciences (12062824). 

RESULTS 

For the 20 healthy adult subjects, we calculated the to- 
tal score of the items that reflected hypersensitivity and 
avoidance in the AASP auditory items. Because the me- 
dian of the scores was 13 points (average ± SD score, 13.6 
± 4.73 points), subjects with scores higher than 13 points 
were grouped into the hypersensitive group (8 females, 2 
males) and those that scored below 13 points were included 
in the non-hypersensitive group (8 females, 2 males). Table 
1 describes participant characteristics. The groups did not 
significantly differ in age, gender, and sweating rate. The 
index for auditory hypersensitivity was significantly differ- 
ent between the groups (t = 7.397, p < 0.001). 

Findings regarding the discomfort with each stimulus 
are shown in Table 2. Based on the Mann-Whitney U tests, 
the degree of discomfort was significantly higher in the hy- 
persensitive group compared with the non-hypersensitive 
group for the stimulations of 80 dB-6,000 Hz (p = 0.005). 
There were no significant differences for the other types of 
stimulations. 

Figure 1 shows an example of a skin sweat response. 
Based on the three-way ANOVA, the group x type of stim- 
ulus X time (before vs. after the first stimulus) interaction 
was not significant for the amount of reaction, but a sig- 



nificant type of stimulus x time (before vs. after the first 
stimulus) interaction was observed for the amount of reac- 
tion (p < 0.001). Moreover, based on a simple main effect 
test of the amount of reaction before and after the stimu- 
lation at each level of stimulation type, a main effect was 
observed for 80 dB-500 Hz (p < 0.001) and 80 dB-6,000 Hz 
(p = 0.003). Group main effects were not observed for any 
type of stimulation. 

When the change in palmar sweating was analyzed with 
a two-way repeated ANOVA, we found that the main effect 
for a group was observed only in the hypersensitive group 
at 80 dB-6,000 Hz (F = 6.654, p = 0.002), while the main 
effect for stimulation count was observed in the non- hyper- 
sensitive group at 80 dB-500 Hz (F = 5.780, p < 0.001), 50 
dB-500 Hz (F = 2.933, p = 0.026), and 20 dB-6,000 Hz (F 
= 3.777, p = 0.008). For 80 dB-6,000 Hz, an interaction (p = 
0.0348) was observed for the groups and stimulation counts. 
However, interaction was not observed in the other trials. 
Moreover, from a simple main effect test of the stimulation 
frequency at each level for every group, a main effect for 
stimulation count was observed in the hypersensitive group 
at 80 dB-6,000 Hz (p = 0.008), 80 dB-500 Hz (p < 0.001), 
50 dB-6,000 Hz (p = 0.033), and 50 dB-500 Hz (p = 0.001). 
However, it was not observed in the non-hypersensitive 
group. 

In the palmar sweating comparison tests between the 
groups for every stimulation count, significant differences 
were observed between the hypersensitive and non-hyper- 
sensitive groups at 80 dB-6,000 Hz (first time, p = 0.0003; 



1090 J. Phys. Then Sci. Vol. 26, No. 7, 2014 

Table 3. Mean \aluc of palmar swcaling \ arialions and slandard dc\ iation in each condition 

80 dB-6,000 Hz 
80 dB-500 Hz 
50 dB-6,000 Hz 
50 dB-500 Hz 
20 dB-6,000 Hz 
20 dB-500 Hz 

Non-hyper 

Hyper: hypersensitive group, Non-hyper: non-hypersensitive group 
Unit: mg/cm^/min 





1st 


2nd 


3rd 


4th 


5th 


Hyper 


0.139±0.217 


0.242±0.299 


0.257±0.302 


0.169±0.212 


0.141±0.182 


Non-hyper 


0.026±0.048 


0.005±0.022 


O.OOliO.Oll 


-0.001±0.015 


-0.009±0.019 


Hyper 


0.215±0.260 


0.294±0.273 


0.23±0.272 


0.156±0.213 


0.154±0.225 


Non-hyper 


0.073±0.137 


0.096±0.183 


0.084±0.168 


0.071±0.133 


0.036±0.074 


Hyper 


0.035±0.060 


0.029±0.070 


0.037±0.093 


-0.001±0.166 


-0.030±0.130 


Non-hyper 


-0.002±0.029 


-0.003±0.033 


-0.005±0.040 


-0.000±0.048 


0.005±0.055 


Hyper 


0.070±0.142 


0.036±0.144 


0.014±0.118 


0.001±0.107 


-0.009±0.091 


Non-hyper 


0.006±0.016 


0.005±0.025 


0.005±0.033 


0.001±0.026 


0.000±0.027 


Hyper 


0.059±0.087 


0.022±0.098 


-0.011±0.120 


-0.022±0.138 


-0.017±0.157 


Non-hyper 


0.001±0.023 


-0.043±0.083 


-0.055±0.111 


-0.062±0.122 


-0.069±0.123 


Hyper 


-0.005±0.021 


0.011±0.130 


0.012±0.150 


0.023±0.107 


0.000±0.096 


Non-hyper 


0.005±0.026 


-0.008±0.018 


-0.020±0.034 


-0.024±0.042 


-0.019±0.055 



second time, p < 0.001; third time, p < 0.001; fourth time, p < 
0.001; and fifth time, p < 0.001), 80 dB-500 Hz (first time, p 
< 0.001; second time, p < 0.001; third time, p < 0.001; fourth 
time, p = 0.049; and fifth time, p = 0.008), 50 dB-6,000 Hz 
(first time, p = 0.0315; third time, p - 0.018; and fifth time, 
p = 0.046), 50 dB-500 Hz (first time, p = 0.001), 20 dB- 
6,000 Hz (first time, p = 0.014; second time, p = 0.007; and 
fifth time, p = 0.026), and 20 dB-500 Hz (fourth time, p = 
0.008). The significant differences in palmar sweating vari- 
ations between the stimulation frequencies in each group 
are shown in Table 3. 

The differences in the variations in palmar sweating 
between the groups with respect to the baseline value and 
after the first stimulation were analyzed with one-way 
ANOVA. Significant differences in the average values were 
not found for all stimulation types. Stimulations in which 
the variances were significantly higher in the hypersensitive 
group compared with the non-hypersensitive group were 20 
dB-6,000 Hz (p < 0.001), 50 dB-500 Hz (p = 0.003), and 80 
dB-6,000 Hz (p = 0.002). 

DISCUSSION 

Although group x type of stimulus x time (before vs. 
after the first stimulus) interactions were not observed for 
the amount of reaction, a significant stimulus x time (be- 
fore vs. after the first stimulus) interaction was observed for 
the amount of reaction. Therefore, these findings suggested 
that auditory stimulation influenced the palmar sweating in 
all of the subjects. Because the variations in palmar sweat- 
ing before and after stimulation were larger for the 80-dB 
stimulation than for the 20-dB and 50-dB stimulations, it 
was likely that the influence on the sympathetic nerves was 
as large as the sound pressure. 

We examined the habituation to stimulation and the dif- 
ferences in palmar sweating after stimulation of the hyper- 
sensitive and non-hypersensitive groups. Because differ- 
ences occurred in the extent of palmar sweating between 
the hypersensitive and non-hypersensitive groups with the 
80 dB-6,000 Hz stimulation, there were possible differenc- 



es in habituation to the auditory stimuli between the groups. 
Additionally, in this regard, significant variations were ob- 
served in the palmar sweating of the hypersensitive group 
from the first to fifth times with the sound pressures of 80 
dB and 50 dB. However, significant variations were not ob- 
served in the non-hypersensitive group. Therefore, these 
findings suggested that, for the non-hypersensitive group, 
the sympathetic nerve response was small, even for large 
sound pressure stimulations. For the hypersensitive group, 
however, the sympathetic nerve response was greater. Thus, 
it can be inferred that a person has a tendency for exces- 
sive autonomic nerve reactions in response to repeated loud 
noises if she/he routinely experiences excessive reactions to 
auditory stimulations. Because variations were observed in 
the transition of palmar sweating between the hypersensi- 
tive and non-hypersensitive groups for the stimulation types 
of 80 dB-6,000 Hz and 80 dB-500 Hz, it was believed that 
there were differences between the groups in their sympa- 
thetic nerve responses to repeated auditory stimuli. In this 
regard, from the first to fifth times, significant variations 
were observed in the palmar sweating of the hypersensi- 
tive group with the sound pressures of 80 dB and 50 dB, 
whereas no significant variations were observed in the non- 
hypersensitive group. Moreover, for the stimulations with 
80 dB-500 Hz and 80 dB-6,000 Hz in the hypersensitive 
group, the amount of sweating clearly increased after the 
second stimulation, unlike in the non-hypersensitive group 
in which significant variations were not observed from the 
first to fifth times. In the hypersensitive group, the main 
effect of frequency was observed for 50 dB-6,000 Hz, and 
variations were observed between the groups in the first, 
third, and fifth times. Therefore, it was inferred that the 
sympathetic nerve responses of the subjects who regularly 
had excessive reactions to auditory stimuli differed from 
those of the persons who did not. 

In a study that used healthy adults as subjects. Brown 
et al.'*^ reported that two groups with high scores for hy- 
persensitivity and avoidance on the AASP had difficulty 
habituating to an auditory stimulation compared with two 
other groups with high scores for low registration and sen- 



1091 



sation seeking. Thus, it can be concluded that habituation to 
stimulation is difficult if a person's scores for hypersensitiv- 
ity and avoidance are high. Moreover, Chang et al.'^* report- 
ed that children with ASD with auditory hypersensitivity 
exhibit high sympathetic activation and strong sympathetic 
reactivity to auditory stimuli and suggested that children 
with ASDs have difficulty habituating to auditory stimuli 
due to persistently strong galvanic skin responses. Further- 
more, the results of this study suggested that the hypersen- 
sitive group felt significantly more discomfort with large 
sound pressures than the non-hypersensitive group did. The 
palmar sweating measured in this study could reflect men- 
tal sweating that is due to emotional changes, such as anger, 
fear, or anxiety. With repeated unpleasant stimuli, subjects 
in the hypersensitive group might have had a persistent 
predominant state of sympathetic nerves because they had 
more psychological burden and were anxiously anticipating 
the next stimulus. 

Before and after the first stimulation, there was a differ- 
ence in the variances for palmar sweating in both groups, 
and the variance of the hypersensitive group was larger than 
that of the non-hypersensitive group. Among the subjects 
who were classified into the hypersensitive group, subtypes 
may have existed depending on the auditory stimuli reac- 
tion pattern. The hypersensitive group may have included 
people who were prone to sympathetic nerve responses due 
to stimulation, people who were prone to excessive sym- 
pathetic nerve responses due to psychological factors, such 
as anxiety caused by repeated stimulation, and people who 
were subjectively hypersensitive but did not have a large 
reaction of sympathetic nerve response due to stimulation. 

This study found that people with auditory hypersen- 
sitivity traits had different sympathetic nerve responses 
to repetitive and large sound pressure stimuli. There was 
no differentiation of the sympathetic nerve responses be- 
tween 500 Hz and 6,000 Hz. However, sound pressure had 
an impact on the sympathetic nerve responses. People with 
auditory hypersensitivity traits may have a tendency for ex- 
cessive sympathetic nerve reactions to sound in daily life. 
These findings suggested that therapists might play a role 
in helping people with auditory hypersensitivity traits to 
evaluate their needs in detail and discuss with their families 
their options for interventions, such as excluding unpleas- 
ant sounds. 



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