Shinshu M ed J, 64⑶ :123〜133, 2016

Functional Magnetic Resonance Imaging Study of Brain Activation
by Sound Localization in Artiﬁcial Unilateral Hearing Loss
Tsuyoshi MATSUSHITA , Takayuki M ITSUI , Tomoki KANEKO
Hitoshi UEDA and Masumi KADOYA
1) Department of Radiology, Shinshu University School of Medicine
2) Department of Diagnostic Radiology, Nagano Municipal Hospital3) Radiology Division, Shinshu University Hospital

Purpose: We aimed to identify brain activation on functional magnetic resonance imaging after a soundlocalization task in artiﬁcial unilateral hearing loss using an earplug.
Materials and M ethods:Subjects were 16 healthy volunteers who were divided equally into the right hearing
loss group (R group)and the left hearing loss group (L group).Sound stimuli were stereo and pure tone of 2000
Hz with varying right and left amplitude ratios.Using a block design,sound stimuli were randomly presented
to the subjects every 2 sec into the task. We investigated the activation areas under conditions of normal
hearing (NH)and artiﬁcial unilateral hearing loss (UHL). The analysis region was focused on the combined
Heschlʼs and superior temporal gyri.In addition,the % signal change was calculated to examine hemisphericlaterality of the hemisphere.
Results:In artiﬁcial unilateral hearing loss, signiﬁcant activation in response to the sound localization task
was observed in the hemisphere ipsilateral to the ear with hearing loss. The % signal change of the righthemisphere was signiﬁcantly higher in the R group under UHL conditions and that of the left hemisphere wassigniﬁcantly higher in the L group under NH conditions.In the analysis of laterality index (LI)and LI of eachindividual after wearing the earplug, the shift of laterality was right predominance.
Conclusion :In an artiﬁcial acute‑phase UHL, the ipsilateral combined Heschlʼ
s and superior temporal gyri
showed signiﬁcant activation in a sound localization task. The right hemisphere was suggested to be thedominant brain region associated with sound localization. Shinshu Med J 64 : 123 ―133, 2016
(Received for publication December 7, 2015;accepted in revised form January 13, 2016)
Key words:functional MRI, sound localization, unilateral hearing loss, auditory cortex, laterality

Introduction
Sound localization identiﬁes the location of a

auditory cortex (temporal lobe), premotor cortex,
and parietal lobe have been previously reported tobe the brain regions associated with sound localiza-sound source based on interaural intensity diﬀer-tion,but this conclusion cannot be conﬁrmed forence (IID) and interaural time diﬀerence (ITD) .

the laterality of the cerebral hemisphere.In healthy

Therefore, in patients with unilateral hearing loss

individuals,contralateral auditorycortex activation(UHL),sound localization is impaired .UHL is notof the stimulated ear becomes dominant . How-

uncommon and can be congenital or acquired. The

ever, there were reports of bilateral activation inchronic UHLs

Corresponding author:Tsuyoshi Matsushita
Department of Radiology, Shinshu University School of
Medicine, 3‑1‑1 Asahi, M atsumoto, Nagano 390‑8621,. This is likely due to the plastic-

ity of the central nervous system for recovery andadaptation. Scheﬄer et al. reported that plasticity

Japanor reorganization occurred in the auditory pathway

E‑mail:matusita＠shinshu‑u.ac.jp

of UHL patients .

No. 3, 2016123

Matsushita.M itsui.Kaneko et al.

In patients recovering from hemiplegia due tocerebral infarction, some have reported brain activation on the contralateral hemisphere or aroundthe area of cerebral infarction. To increase

brain plasticity,rehabilitation should focus on training the aﬀected extremities,rather than the normal
extremities for compensation. Similarly, in

UHL, there is a possibility that plasticity of thebrain may lead to a certain degree of improvementin the ability to localize sound. In order to achieve
better recovery, more extensive rehabilitation
would be needed to eﬀectively activate the diseased

Fig. 1

Diagram of fMRI scan and acoustic stimulation timing
For silent auditory fM RI studies, the duration ofdata acquisitions is 2.5 sec in TR (10 sec).
fMRI, functional magnetic resonance imaging ;TR, repetition time

area. By identifying the brain regions associatedwith impaired function (sound localization), it may

Japan (No. 2163). All participants gave written in-

become possible to select the method of rehabilita-

formed consent to the experimental protocol.

tion to activate the associated brain regions more

B Data acquisition
The experiment was conducted using a 3‑T whole‑eﬀectively.
In addition, Okamoto et al.

performed soundbody M RI scanner (M agnetom Trio ; Siemens, Er-therapy for patients with sudden sensorineural hear-langen, Germany) with a 32‑channel head coil sys-

ing loss and determined the therapeutic eﬀects usingtem. For BOLD‑based imaging , spin‑echo planar

the audiogram and magnetoencepalography. Using

images of the entire brain were acquired in thefunctional magnetic resonance imaging (fMRI),transverse orientation (repetition time (TR)＝10 s;there is a possibility to verify more detailed thera-echo time (TE)＝30 msec; ﬂip angle 90°; ﬁeld of

peutic eﬀects of hearing loss. Therefore, in UHLview(FOV)＝192×192 mm ;64×64 matrix ;40 inter-cases in the acute phase,it may be useful to identify

leaved slices 3‑mm thick and with slice gaps of 0.75

the main brain activation region as the basis of themm). In auditory studies using fMRI, there is apre‑treatment.

possibility that the acoustic scanner noise aﬀects

As a preliminary study, we aimed to identify

the experiment. In order to reduce this eﬀect,

brain activation on fMRI after a sound localization

Scheﬄer et al. performed an experiment in whichtask in artiﬁcial unilateral hearing loss conditions

the duration of data acquisition was 1.8 sec in TR

using an earplug.

(15 sec) . Based on their settings, the duration of

M aterials and M ethods
A Subjects

data acquisition during silent auditory fMRI studies
was 2.5 sec in TR (10 sec) in our study (Fig. 1). In
addition, high‑resolution T1‑weighted anatomical

Sixteen right‑handed volunteers, 10 men and 6

images were acquired using an MP‑RAGE sequence

women with ages ranging from 22 to 58 years(TR＝2.3 s; TE＝2.98 msec; TI＝900 msec; ﬂip(mean, 29.9 years), participated in this study. Allangle 9°;FOV＝256×240 mm ;256×230 matrix,160

subjects were healthy individuals with no history ofsagittal slices 1.1‑mm thick).

neurologic diseases. They were randomly divided

C Stimuli and tasks

into two equal halves, based on the location of the

In this study,we used sound stimuli generated byearplug (E.A.R. Classic): the right UHL group (RIID in MatLab 8.2 (The MathWorks Inc., Natick,group,n＝8)and the left UHL group (L group,n＝8).

M A, USA) because UHL was considered to haveThis study was approved by the institutional

more adverse eﬀects on IID than on ITD. Elevenreview board of Shinshu University, M atsumoto,sound stimuli on the right ear and left ear were

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Brain activation during sound localization in unilateral hearing loss

stereo and pure tone with varying amplitude ratios.

implemented in M atLab 8.2 (The M athWorks Inc.,

The frequencyof these sounds was 2000 Hz,because

Natick,MA,USA).The ﬁrst image of each run wascues of sound localization at a frequency of morediscarded to allow the MRI signal to reach a steadythan 1500 Hz are mainly from IID . To achieve

state.The remaining scans were adjusted according

constant energy for each sound stimulus,the cumu-

to slice timing and were realigned to the mean

lative squared amplitude on the right and left was

image to correct for head movements.Images weremade constant. Sound stimuli had a duration of 1

co‑registered to the individual anatomical T1‑

sec and were gated on and oﬀwith 40msecofraised‑weighted images and were normalized to the MNI

cosine ramps.

space by applying a uniﬁed segmentation normaliza-

Auditory stimuli were presented to the subjects

tion procedure. Finally, images were smoothedthrough fMRI‑compatible headphones (VisuaStim ;using an 8‑mm Gaussian kernel.

Resonance Technologies, Inc.). Sound volume was

E Data analysis

adjusted so that each subject could hear the stimuli

We investigated the brain activation areas underproperly, but not at excessive and painful volumes.

NH and UHL conditions.The auditory cortex (tem-Consequently,volume was constant for all subjects.

poral lobe),premotor cortex,and parietal lobe have

Stimulus presentation and synchronization with the

been previously reported to be the brain regions

MR system were controlled bypresentation software

associated with sound localization(Neurobehavioral Systems, Albany, NY, USA).

examined these areas as the evaluation target. In. We also

Response devices with four buttons on the front

our study,because it was suspected that movement

were placed on both hands (under the thumb)of theof the subjectʼ
s ﬁngers to operate the button devices

subjects and were opticallyconnected to a computerinﬂuenced the motor and sensory areas, the frontal

outside the scanner room. In our experiment one

lobe and the parietal lobe were excluded frombutton was used of the four buttons of the devices

evaluation. The analysis region was focused on theon both sides. Subjects were instructed to indicate

combined Heschlʼ
s and superior temporal gyri, in-the location of the presented sound by pressing thecluding the auditory cortex. The activation areas

right and left buttons accordingly.They pressed theunder NH and UHL conditions were identiﬁed forright side button if the sound source was identiﬁed

the R and L groups.Group analysis was performedon the right side, the button with both hands if it

on a ﬁxed eﬀect model to detect areas of signiﬁcant

was identiﬁed in the center,and the left side buttonchanges in brain activity under the four task condi-

if it was identiﬁed on the left side.

tions (NH in the R group,UHL in the R group,NH

Using a block design, sound stimuli in a pseudor-

in the L group, and UHL in the L group). The

andom order were presented every 2 sec into thethreshold was set at p ＜ 0.05 for multiple compari-task ;silence was maintained during the remaindersons using FWE (family wise error). Individualof the task. One set was composed of the task (30analysis was conducted at a threshold value ofsec)and the rest (30 sec), and 1 section (8 min)was

uncorrected p ＜ 0.001.

composed of the 8 sets.Subjects performed 1 section

In addition, the % signal change in the region ofunder normal hearing (NH) conditions, and then 1

interest (ROI)was calculated and analyzed to exam-

section under artiﬁcial UHL conditions using an

ine for laterality of the hemisphere. Because theearplug. All subjects received the same training incluster size in the contralateral hemisphere wastask performance prior to fMRI.

about 0 under the UHL conditions,evaluation usingD

cluster size was estimated to be diﬃcult and in thisPreprocessing
Data were pre‑processed and analyzed using

study we therefore used the % signal change.Using

Statistical Parametric M apping (SPM12;Wellcome

M arsBaR AAL ROI package, the combined bilat-

Department of Imaging Neuroscience,London,UK)

eral Heschlʼ
s and superior temporal gyri, including

No. 3, 2016125

Matsushita.M itsui.Kaneko et al.

the auditory cortex, were deﬁned as ROIs . Using

In addition,we examined the changes in laterality

SPM Anatomy toolbox, the combined bilateralfor each subject after wearing the earplug. The

Brodmannʼs area 41(BA41)and Brodmannʼs area 42

threshold LI value was set at 0.2, according to a

(BA42), which corresponded to the auditory cortex,

previously reported rule . In each subject, later-

were deﬁned as ROIs

.ROI analysis was conduct-

ality was classiﬁed as left hemispheric dominanceed using M arsBaR toolbox for SPM (http://mars-(LI＞0.2), bilateral dominance (LI 0.2), or rightbar.sourceforge.net) . The clusters were separated

hemispheric dominance (LI＜−0.2).

individually to derive the % signal change for NH

Results

and UHL.
Wilcoxon signed rank test was performed bet-

Brain activations were observed bilaterally in theween the values on each side. In order to examine

R and L groups under NH conditions (Fig. 2A,

whether there was a shift in laterality due to UHL,

Table 1).The cluster size of the left hemisphere was

the laterality index (LI)was calculated from the %greater than that of the right hemisphere. Undersignal change. The LI was calculated based on the

UHL conditions,brain activations were observed inprevious report as the following formula

the ipsilateral hemisphere. The main signiﬁcant:

LI＝(LH−RH)/(LH ＋ RH )activation was observed in the ipsilateral BA41 andwhere LH represents the % signal change of theBA42 areas (Fig. 2B).

left hemisphere ROI and RH represents the %The % signal changes in the combined Heschlʼ
ssignal change of the right hemisphere ROI.If the LI

and superior temporal gyri of each hemisphere andwas a negative value, the right hemisphere wasunder both NH and UHL conditions are shown in

dominant ; if the LI was a positive value, the left

Fig. 3. In the R group, the % signal changes were

hemisphere was dominant. Wilcoxon signed rank

0.6455±0.2972 on the left hemisphere and 0.5651±

test was performed to compare values between NH

0.3263 on the right hemisphere under NH condi-

and UHL conditions.

tions;and 0.2286±0.2312 on the left hemisphere andTable 1 Functional magnetic resonance imaging data on brain regions activated during sound localization task
Threshold was set at p＜0.05 for multiple comparisons using FWE.
R group, right unilateral hearing loss group ; L group, left unilateral hearing loss group ; MNI, Montreal
Neurological Institute;FWE, family wise errorGroup

Condition

RegionCluster size

T‑value MNI coordinates
x

y

z

12
‑2
12

R group
Normal hearing

Unilateral hearing loss

L Superior Temporal Gyrus
L Superior Temporal Gyrus
L Superior Temporal Gyrus

1079

11.73
7.15
6.23

‑48
‑52

‑30
‑2

‑64

R Superior Temporal Gyrus
R Superior Temporal Gyrus

772

9.1
8.66

66
64

8.63
5.7

54
56

‑14
‑2
‑10
‑24
‑20

‑48
‑34

R Superior Temporal Gyrus
R Superior Temporal Gyrus

82

2
6
12
10

L group
Normal hearing

Unilateral hearing loss
126

L Superior Temporal Gyrus
L Heschlʼs Gyrus
R Superior Temporal Gyrus
R Superior Temporal Gyrus
L Superior Temporal Gyrus

251

56

7.31
5.11
5.84
4.87
5.46

L Superior Temporal Gyrus

115

6.39

100

54
44
‑50
‑46

‑34
‑32
‑20
‑32
‑6
‑36

12
14
10
14
‑4
12

Shinshu Med J Vol.64

Brain activation during sound localization in unilateral hearing loss

Fig. 2 Images of brain activation to sound stimuli under NH and UHL conditions
A. The analysis region was focused on the combined Heschlʼ
s and superior temporal gyri, including the auditory
cortex. B. The analysis region was focused on combined BA41 and BA42, which corresponds to the auditory cortex.
In A and B respectively, the upper row shows the set of the R group and the set of the L group under NH conditions
and the lower row shows the set of the R group and the set of the L group under UHL conditions.One set presents threeorthogonal projections. The RH and LH letters on the images indicate the right and left hemispheres, respectively.
The threshold was set at p＜0.05 and corrected with FWE.
NH, normal hearing ; UHL, unilateral hearing loss; R group, right unilateral hearing loss group ; L group, left
unilateral hearing loss group ;FWE, family wise error
No. 3, 2016127

Matsushita.M itsui.Kaneko et al.

Fig. 3 % signal change of the combined Heschlʼ
s and superior temporal gyri
The % signal change of the right hemisphere was signiﬁcantly higher than that of the left hemisphere in UHL
conditions in the R group. The % signal change of the left hemisphere was signiﬁcantly higher than that of the righthemisphere in NH conditions in the L group.
The boundary of the box closest to 0 represents the 25th percentile,whereas that farthest from zero corresponds tothe 75th percentile. Lines in boxes represent the median. Error bars show minimum and maximum values.
p＜0.05NH, normal hearing ; UHL, unilateral hearing loss; LH, left hemisphere; RH, right hemisphere; R group, right
unilateral hearing loss group ;L group, left unilateral hearing loss group0.3270±0.3166 on the right hemisphere under UHL
conditions. In the L group, the % signal changes
were 0.5104±0.6065 on the left hemisphere and0.3825±0.5514 on the right hemisphere under NH
conditions; and 0.4936±0.5791 on the left hemisphere and 0.4366±0.7511 on the right hemisphere
under UHL conditions. In the right hemisphere, %signal change was signiﬁcantly higher in the R
group under UHL conditions (p＝0.0234).In the left
hemisphere, % signal change was signiﬁcantly
higher in the L group under NH conditions (p＝Fig. 40.0234). A signiﬁcant diﬀerence was not observed

Heschlʼs and superior temporal gyri
The laterality index of the NH condition wasunder NH conditions in the R group and under UHL
conditions in the L group.
The LI of the combined Heschlʼ
s gyrus and superior temporal gyrus are shown in Fig. 4. In the R
group, the LI of the UHL was signiﬁcantly lower
than that of the NH (−0.3974±0.4171 vs. 0.1021±
0.1883, p＝0.0078). In the L group, LI was 0.2116±
0.3049 under NH conditions and 0.2796±0.4750
under UHL conditions.
The % signal change of the combined BA41 andThe laterality index in the combined

signiﬁcantly higher than that of the UHL condition in
the R group.
The boundary of the box closest to 0 represents the25th percentile,whereas that farthest from zero corresponds to the 75th percentile.Lines in boxes represent
the median.Error bars show minimum and maximum
values.
p＜0.01
NH,normal hearing ;UHL,unilateral hearing loss;
R group,right unilateral hearing loss group ;L group,
left unilateral hearing loss group

BA42 are shown in Fig. 5. In the R group, the %signal changes were 1.098±0.1777 on the left hemisphere and 1.183±0.1883 on the right hemisphere
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Brain activation during sound localization in unilateral hearing loss

Fig. 5 % signal change of combined BA41 and BA42
The% signal change of the right hemisphere was signiﬁcantly higher in UHL conditions in the R group.The% signal
change of the right hemisphere was signiﬁcantly higher in the NH condition and the UHL condition of the L group.
The boundary of the box closest to 0 represents the 25th percentile,whereas that farthest from zero corresponds to the75th percentile. Lines in boxes represent the median. Error bars show minimum and maximum values.
p＜0.05NH, normal hearing ; UHL, unilateral hearing loss; LH, left hemisphere; RH, right hemisphere; R group, right
unilateral hearing loss group ;L group, left unilateral hearing loss group

under NH conditions;and 0.6663±0.2822 on the left
hemisphere and 0.7616±0.1578 on the right hemisphere under UHL conditions.In the L group,the%signal changes were 1.189 ±0.1767 on the left hemisphere and 1.290±0.1262 on the right hemisphere
under NH conditions; and 0.7909 ±0.06297 on theleft hemisphere and 0.8764±0.06773 on the righthemisphere under UHL conditions. In the R group,% signal change in the right hemisphere wassigniﬁcantly higher under conditions of UHL (p＝0.0156) than that in the left hemisphere. In the L

Fig. 6The laterality index in the combined
BA41 and BA42

group,% signal change in the right hemisphere was

There is no signiﬁcant diﬀerence between NH and
UHL conditions in both groups. The boundary ofsigniﬁcantly higher under conditions of NH (p＝the box closest to 0 represents the 25th percentile,

0.0156) and UHL (p＝0.0142) than that in the left

whereas that farthest from zero corresponds to the75th percentile.Lines in boxes represent the median.

hemisphere.
The LI of the combined BA41 and BA42 areshown in Fig. 6.In the R group,LI was −0.03728±
0.1078 under NH conditions and −0.1557±0.3421

Error bars show minimum and maximum values.
NH, normal hearing ; UHL, unilateral hearing
loss;R group,right unilateral hearing loss group ;Lgroup, left unilateral hearing loss group

under UHL conditions. In the L group, LI was−0.04280±0.02633 under NH

conditions andchlʼ
s and superior temporal gyri, shift to the right−0.05179 ±0.02498 under UHL conditions. LI was

was seen in 6 subjects, no change in 2 subjects,and

not signiﬁcantly diﬀerent between NH and UHL

shift to the left in no subjects in the R group.In theconditions in both groups.

L group,shift to the right was seen in 2 subjects,noTable 2 shows the LI and shift in laterality of thechange in 5 subjects,and shift to the left in 1 subject.

hemisphere in each subject after wearing earplugs.

In terms of laterality shift of the combined BA41

In terms of laterality shift of the combined Hes-

and BA42,shift to the right was seen in 1 subject,noNo. 3, 2016129

Matsushita.M itsui.Kaneko et al.
Table 2Laterality shift after wearing earplugs
LI, laterality index

A. Combined Heschlʼ
s gyrus and superior temporal gyrus
R group
L group
Subject
numbernormal hearing unilateral healinglaterality
condition
loss conditionshift
LI laterality
LI
laterality01

0.15 bilateral

03
05
08

0.04 bilateral
0.53
left
0.00 bilateral09
11

0.16 bilateral
0.02 bilateral13
16

0.00 bilateral‑0.08 bilateral

‑0.97
‑0.64
0.04
0.00
‑1.00
‑0.25
‑0.21
‑0.15

right

right

right
right
bilatcralrightbilateral no change
right
right

right
right

right
right
bilateral no change

B. Combined BA41 and BA42
R group
Subject
number
01
03
05
08
09
11
13
16

‑1.00
‑0.05
‑0.03
‑0.08

‑0.05 bilateral‑0.10 bilateral‑0.03 bilateral‑0.07 bilateral

0.00
‑0.04
‑0.01
‑0.05

normal hearing unilateral healinglaterality
condition
loss conditionshift
LI laterality
LI
laterality02

0.10 bilateral

04
06
07

0.30
left
0.03 bilateral
0.90
left

10
12

0.21
left
0.21
1eft
‑0.07 bilateral

14
15

0.01 bilateral

0.06
‑0.18
‑0.02

bilateral no change

1.00

bilateralrightbilateral no change
left
no change

0.41
‑0.05

left
no ohangebilateral
right

1.00
0.02

left
left
bilateral no change

L groupnormal hearing unilateral healinglaterality
condition
loss conditionshift
LI laterality
LI
laterality
0.22
left
‑0.10 bilateral‑0.06 bilateral‑0.11 bilateral

Subject
number

right

right

Subject
number02

bilateral no changebilateral no changebilateral no changebilateral no changebilateral no changebilateral no change

04
06
07
10
12
14

bilateral no change

15

normal hearing unilateral healinglaterality
condition
loss conditionshift
LI laterality
LI
laterality
0.01 bilateral‑0.04 bilateral‑0.06 bilateral‑0.06 bilateral

‑0.09
‑0.04
‑0.05
‑0.06

‑0.08 bilateral‑0.04 bilateral‑0.03 bilateral‑0.03 bilateral

‑0.01
‑0.08
‑0.05
‑0.04

bilateral no changebilateral no changebilateral no changebilateral no changebilateral no changebilateral no changebilateral no changebilateral no changechange in 7 subjects, and shift to the left in nonant . Assuming that our study simulated unilat-

subjects in the R group.In the L group,shift to theeral ear stimulation by wearing earplugs,this resultright was seen in no subjects, no change in 8 sub-was consistent with that of previous reports.

jects, and shift to the left in no subjects.

Bilecen et al.reported a case of UHL after excision

Discussionof a right auditory nerve tumor . In the report,
although strong activation was observed to beright‑

In this study,activations in the combined Heschlʼ
sdominant on fMRI in the ﬁrst postoperative week,itand superior temporal gyri, including the auditory

was almost bilateral after more than one year. If

cortex (BA41 and BA42), were evaluated. Under

the artiﬁcial UHL condition in our study was

NH conditions, brain activations were observed onassumed to simulate clinical acute UHL,our results

both sides. The cluster size on the left side waswere consistent with this report.

larger than that on the right side, and may be

After wearing earplugs, the cluster size of the

explained by the anatomicallylarger Heschlʼ
s gyrusactivated area was reduced at the hemisphere ip-

on the left

. Under UHL conditions, the mainsilateral to the ear with hearing loss.Because UHL

signiﬁcant activation was observed in the auditory

sessions were performed after NH sessions, it wascortex ipsilateral to the ear with hearing loss. In

considered that brain activation was reduced byhealthy subjects, auditory cortex activation con-habituation and repetition .

tralateral to the stimulated ear becomes domi130

In the analysis of the % signal change of theShinshu Med J Vol.64

Brain activation during sound localization in unilateral hearing loss

combined Heschlʼ
s and superior temporal gyri, thepossible that these factors aﬀected our results.

right hemisphere became signiﬁcantly dominant

Our study had some limitations.Firstly,our study

under UHL conditions in the R group. In the L

was limited by the small sample size.In the analysis

group, the left hemisphere was signiﬁcantly domi-of the % signal change, under NH conditions, anant under NH conditions, but there was no later-

signiﬁcant diﬀerence was not observed in the R

ality under UHL conditions. We expected that ip-

group,but was observed in theL group(Fig.3,Fig.5).

silateral (left) hemisphere dominance would be

It was considered that these results had beenclearer under UHL conditions in the L group, but

aﬀected by the bias between the R group and the L

our result was diﬀerent.In the analysis of LI of eachgroup.Secondly,subtraction of NH data,as control,

individual after wearing earplugs, shift to the rightfrom UHL data would have been ideal to identify

side was the most commonly observed trend in theand evaluate changes in the activation area afterR group and the second most common trend in thewearing earplugs. The protocol of performing theL group.Among ﬁve subjects with no change in the

UHL experiments after the NH experiments may

L group,two subjects demonstrated left hemispher-have attenuated some brain activations under theic dominance under NH conditions. It is possible

UHL conditions due to habituation and repetition .

that displacement to the left side was masked.

M oreover, UHL in this study was simulated by

However, compared with the R group, the L groupusing earplugs on one side,instead of unilateral ear

had a weaker tendency for shift in laterality ip-

stimulation without using earplugs, which would

silateral to the side of hearing loss.

have simulated a diﬀerent condition (deafness).

In the analysis of the % signal change and the LI

Because it was necessary to attach the earplugs, itof the combined BA41 and BA42, the right hemi-

was not feasible to set up two conditions in one

sphere was signiﬁcantly dominant under UHL con-session. Therefore, we could not successfully per-ditions in the R group,but the LI remained constant.

form the subtractions.Third,experiments under the

In the L group, the right hemisphere was signiﬁ-

three conditions (NH,right UHL,and left UHL)forcantlydominant under NH and UHL conditions,but

each subject were ideal.However,extended experi-

the LI remained constant.In terms of individual LI,

ment time and decreased concentration of subjects

change in laterality was poor after wearing ear-

were avoided.Fourth,in our study duration of dataplugs.

acquisitions was 2.5 sec in TR (10 sec) for silent

Therefore,in the combined Heschlʼ
s and superior

auditory fMRI studies.The images were not able totemporal gyri, excluding the auditory cortex, there

be captured in the remaining 7.5 sec. In the usual

may be regions in which the % signal change

fMRI, activation areas have been identiﬁed underbecomes right‑dominant after wearing earplugs. In

presumed or typical hemodynamic response during

general, attention eﬀects on the auditory cortex

a task . In the auditory cortex, there are regions

increase along with task diﬃculty . In the com-

exhibiting a diﬀerent pattern of blood ﬂow

bined Heschlʼ
s and superior temporal gyri, thechangeregions associated with characteristic sound stimuli

ﬂow pattern may be diﬃcult with the settings that

may be activated predominantly in the right hemi-

we used in this study.To capture blood ﬂow changes

sphere with increasing task diﬃculty.Based on ourin detail,it would be necessaryto attenuate acoustic

results,the right temporal lobe was suggested to benoise at the time of image acquisition.

the dominant brain region associated with soundlocalization. However, the stimulus sound that we. Therefore, detailed evaluation of blood

Conclusion

used in this studywas non‑verbal.There are reports

In an artiﬁcial acute‑phase UHL, the ipsilateralthat non‑verbal sound stimulation is predominantly

combined Heschlʼ
s and superior temporal gyriassociated with the right hemisphereshowed signiﬁcant activation in a sound localization

No. 3, 2016

. It is also131

Matsushita.M itsui.Kaneko et al.

task.Asymmetrical shift of laterality was observed

Acknowledgment

after wearing an earplug. The right temporal lobe
was suggested to be the dominant brain region
associated with sound localization.

The authors would like to thank Enago (www.
enago.jp)for the English language review.

Conﬂict of Interest
There are no conﬂicts of interest to declare.
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