an “expectation effect” in the task-based experiment, the six different
tone stimuli and quiet baseline stimuli were presented in an alternating
pseudo random pattern. The intensity of all stimuli was 75 dB, but due
to differences between individuals, participants could adjust the loud-
ness of the tone bursts between 70 and 80 dB.
2.3
|
Procedure
For each subject, three types of MRI data were acquired on the same
day: resting-state fMRI, task-based fMRI, and T1 image data. To elimi-
nate any possible influence of task execution, resting data were col-
lected prior to task-based data collection, which was then followed by
high-resolution T1-image data collection (Figure 1). To improve the sta-
tistical effectiveness of each single subject, multiple task-based fMRI
runs were used to increase the total number of trials. During the audi-
tory task, participants were only asked to stay awake and passively lis-
ten to the stimuli (Cha et al., 2016; Hu et al., 2017). The stimulus
sequence was played via MR-compatible high-fidelity headphones
(Optoacoustics) that used an adaptive DSP-based noise-reduction
filtering algorithm.
All images were collected on a 3.0-T Siemens (Erlangen, Germany)
scanner. The resting-state data were collected using an echo-planar
imaging (EPI) sequence (FOV 5 220 3 220 mm, acquisition
matrix 5 64 3 64 mm, pixel spacing 5 3.43753 3.4375 mm, slice
thickness 5 3.0 mm, TR 5 2000 ms, TE 5 30 ms, flip angle 5 908). The
task-based functional images were sampled using a 10-min EPI
sequence (FOV 5 220 3 220 mm, acquisition matrix 5 64 3 64 mm,
pixel spacing 5 3.4375 3 3.4375 mm, slice thickness 5 3.0 mm,
TR 5 3400 ms, TE 5 26 ms, flip angle 5 908). High spatial resolution
3D-T1 anatomical data were gathered using a magnetization-prepared
rapid gradient-echo (MPRAGE) sequence (FOV 5 246 3 256 mm,
acquisition matrix 5 246 3 256, pixel spacing5 1 3 1 mm, slice
thickness 5 1mm,TR5 1900 mm, TE 5 2.52 mm, flip angle 5 908).
2.4
|
Task-based fMRI data analysis
All task-based fMRI data were preprocessed using SPM8 (http://www.
fil.ion.ucl.ac.uk/spm/software/spm8
/). As the magnetic field of the
scanner may be unstable during the initialization phase, the first ten
volumes for each subject were discarded (Dresler et al., 2017; Yao
et al., 2016). Therefore, only the remaining 170 volumes were used for
the subsequent analysis. The preprocessing of task-based fMRI data
included the following steps: slice timing (interlayer time correction),
realignment (head motion correction), co-registration (T1 images were
co-registered to the mean functional image), segmentation (T1 images
were divided into gray matter, white matter, and cerebrospinal fluid),
normalization (functional and structural imaging data were spatially nor-
malized to the Montreal Neurological Institute (MNI) EPI template
using DARTEL; Ashburner, 2007), and spatial smoothing (using a 3D
Gaussian kernel, full maximum at half width (FWHM) 5 6mm).Dueto
head movement issues (translational (mm) > 2.0 or rotation (8) > 2), six
task-based image datasets were discarded after preprocessing.
A general linear model (GLM) was applied to each voxel time
series, and each frequency condition was modelled with a separate
regressor constructed by convolving a boxcar function with a hemody-
namic response function provided by SPM8. Six motion parameters
were included in the model as nuisance regressor. One sample t tests
of beta maps were used to examine brain activation levels under each
frequency condition at the group level (p < .001, cluster size 5 10,
uncorrected). BrainNet Viewer (http://www.nitrc.org/projects/bnv)
(Xia, 2011) was used to map these activation maps to the same surface
map (Fig. 2). Points on the surface map that showed significant differ-
ences across frequencies (i.e., tonotopy) were labeled by assigning the
frequency x as the value of each given voxel if its beta value of fre-
quency x was the highest value. This method was similar to the method
performed by Humphries et al., 2010. The Brainnetome Atlas (Fan
et al., 2016) was used to fractionize the tonotopic areas in the HAC
(Supporting Information, Figure S1 and Table S1).
2.5
|
ROIs definition
The WFU PickAtlas (http://www.nitrc.org/projects/wfu_pickatlas/)
was used to produce ROIs. Each seed region is a sphere with a 5 mm
radius, and the center of each sphere is the peak point of each activa-
tion area. Multiple comparisons (p
FDR
<0.05, cluster 5 10) were per-
formed to select the peak points of each activation area used to
generate seed regions (Supporting Information, Table S2). Finally, the
WFU PickAtlas was used to combine the peak-point coordinates of
each frequency into a ROI. Six ROIs were defined based on the
responses of the 50 participants to the six pure tone frequencies, then
these ROIs were divided into three categories, that is, a high-frequency
(3200 and 6400 Hz), intermediate-frequency (800 and 1600 Hz), and
FIGURE 2 Tonotopic organization of the HAC. Heschl’sgyrusis
roughly surrounded by the white dotted line. Colored regions in
the bilateral hemispheres show voxels of s ignificantly different
frequencies, and the color of each voxel represents the frequency
that showed the highest activation response of the six frequency
tone stimu li [Color figure can be viewed at wileyonlinelibrary.com]
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