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20

Methods

Subjects were recruited and informed consent was obtained in accordance with
the University of Texas Committee for the Protection of Human Subjects. Four male
participants and four female participants were scanned using a 3 tesla whole-body
magnetic resonance (MR) scanner (Phillips Medical Systems, Bothell, WA). Anatomical
images were collected using a magnetization-prepared 180° radio-frequency pulses and
rapid gradient echo sequence optimized for gray-white matter contrast with l-mm-
thick sagittal slices and in-plané resolution of 0.938 X 0.938 mm. Functional images were
collected using a gradient recalled-echo echo-planar-imaging sequence sensitive to the
blood-oxygen level dependent (BOLD) signal. Thirty-three axial slices were collected in
each 2 s repetition time (TR) with an echo time of 30 ms and a flip angle of 90°. Slice
thickness was 3 mm, and in-plane resolution was 2.75 X 2.75 mm.

Vibrotactilestimulation

Somatosensory stimuli were delivered to subjects using a custom-built apparatus
(Yasar and Beauchamp 2006). Five piezoelectric bending elements (Piezo Systems,
Cambridge, MA) were attached, one each to the palm of the left and right hand, the sole
of the left and right foot, and the right hip using nonslip silicon elastic bandages. A 200
Hz sinusoidal waveform was used to drive the piezoelectric bending elements (benders),
based on behavioral data showing low detection thresholds at this frequency (Brisben,
et al. 1999).

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