2.2. Tactile stimuli and experimental protocol
During MRI acquisition, a trained experimenter (author JJT) manually
applied gentle brush strokes to the infants’ right anterior shin region
(along the tibia) in a proximal to distal direction. This site was
chosen due to ease of access, as the babies were wrapped in a vacuum
mattress that blocked upper extremities. Also, the investigator leaned
on the scanner bed, leaning slightly toward the scanner bore, without
touching the infant, whilst delivering the stimuli. The length of the
stimulated area was measured to cover 15 cm, and brush strokes were
applied at a velocity of 3 cm/s for 15s, with randomized inter-stimulus
intervals of 10–15 s (resulting in 3 strokes in one 15 s block). The
experimenter was guided by auditory cues delivered through the scanner
head phones. A total of 11 stimuli were applied.