72
time--->
FigureLMethodsusedforsomatosensorymultivoxeIpatternanaIysis.
A. Somatosensorystimuli were delivered by five piezoelectric benders. In experiment 1, the benders
were located on the palm of the right hand (R), the palm of the left hand (L), the sole of the right foot
(D), the sole of the Ieftfoot (S), and the right hip (H).
B. In experiment 2, the benders were located on the right thumb (T), the right middle finger (M), the
right fifth pinky finger (P), the right hip (H) and the right foot (D).
C. During the course of an MRI scan series, brain volumes were acquired (shown schematically by
single brain slices) every 2 sec. Each acquisition corresponded to a single stimulation trial in which a
single body site was stimulated, shown by a letter corresponding to the body plan shown in (A). Some
trials (not shown) contained target bender stimulation or fixation baseline with no somatosensory
stimulation.
D. Using the MR data, an activation map was constructed of voxels responding significantly more (p <
10-6) to somatosensory stimulation than to fixation baseline. A lateral view of a partially inflated left
hemisphere is shown, yellow color shows active areas (Argali, et a∣. 2006).
E. Over the course of a scan series, 150 brain volumes were acquired. The three black traces show the
image intensity over the course of a scan series in three active voxels selected from the yellow voxels
in (C).
F. The time series from all active voxels (E) and the stimulus ordering (C) were used to train an N-
dimensional support vector machine. Forillustration, a simplified training dataset is shown, with only
two voxels and two stimulus categories (right hand and left hand). Each symbol shows the normalized
MR image intensity during a single trial. The red triangles show the MR image intensity in all right
hand stimulation trials and the blue triangles show the intensity in all left hand stimulation trials. The
solid line shows the separating hyperplane WrXf+ w0 = O calculated by the classifier. The dashed lines
show the canonical hyperplanes WrX/ + w0 E ±1 Trials falling between the separating and canonical
hyperplanes were used as support vectors (indicated by circles). An unknown test trial is classified as
"right hand" if It falls below the solid line and "left hand" If it lies above the solid line.
G. Result of the experiment 1 classifier when tested on a different scan series not used for training.
The actual stimulus ordering presented to the subject is shown in the top row in all black, body part
abbreviations as in (A). The classifier prediction of the stimulus ordering is shown in the bottom row:
green for correct classification, red for incorrect classification. Performance of the classifier in this
scan series was 86% coσect (p < 10-38).