Functional Connectivity Evoked by Orofacial Tactile Perception of Velocity

Abstract

The cortical representations of orofacial pneumotactile stimulation involve complex neuronal networks, which are still unknown. This study aims to identify the characteristics of functional connectivity (FC) evoked by three different saltatory velocities over the perioral and buccal surface of the lower face using functional magnetic resonance imaging in twenty neurotypical adults. Our results showed a velocity of 25 cm/s evoked stronger connection strength between the right dorsolateral prefrontal cortex and the right thalamus than a velocity of 5 cm/s. The decreased FC between the right secondary somatosensory cortex and right posterior parietal cortex for 5-cm/s velocity versus all three velocities delivered simultaneously ("All ON") and the increased FC between the right thalamus and bilateral secondary somatosensory cortex for 65 cm/s vs "All ON" indicated that the right secondary somatosensory cortex might play a role in the orofacial tactile perception of velocity. Our results have also shown different patterns of FC for each seed (bilateral primary and secondary somatosensory cortex) at various velocity contrasts (5 vs 25 cm/s, 5 vs 65 cm/s, and 25 vs 65 cm/s). The similarities and differences of FC among three velocities shed light on the neuronal networks encoding the orofacial tactile perception of velocity.

Keywords: cortical representation; fMRI; functional connectivity; orofacial; pneumotactile stimulation; saltatory velocity.

FIGURE 1

Shows the experimental configuration for the Galileo somatosensory stimulator with pneumatic velocity arrays aligned on the participant from the right philtral column to the right buccal face. White flanged surface of the TAC-Cell was adhered to skin surface with double adhesive colars and 7 TAC-Cells form 5 channels in five colors (red: channel 1 placed two TAC-Cells on the median upper and lower lips; orange: channel 2 placed two TAC-Cells next to the TAC-Cells of channel 1; yellow: channel 3 placed a TAC-Cells next to the channel 2; green: channel 4 placed a TAC-Cell next to channel 3; blue: channel 5 placed a TAC-Cell next to channel 4). The bottom four graphs show the time courses for each velocity and All ON.

FIGURE 2

One run of the fMRI in-scan paradigm indicates a series of pneumotactile saltatory stimuli traversed the skin in a repeating medial-to-lateral direction. There are twenty 40 s long blocks in one run. Each block consisted of one 20 s block of task stimuli presentation and 20 s block of rest. There are five possible task blocks (5, 25, 65 cm/s, All ON, All OFF) randomly presented.

FIGURE 3

Shows ROI-to-ROI based connectivity maps (first row) and connectivity adjacent matrices (second row) for three velocities (5, 25, 65 cm/s). Total six region of interests (ROIs) include bilateral primary somatosensory cortex (L_SI and R_SI), bilateral supplementary somatosensory cortex (L_SII and R_SII), bilateral Posterior Parietal Cortex (L_PPC and R_PPC), bilateral dorsolateral Prefrontal Cortex (L_DLPFC and R_DLPFC), and bilateral thalamus (L_Thalamus and R_Thalamus). The color bar ranges from –1 to 1 and indicates the connectivity strength measured by Pearson’s correlation coefficients. On the connectivity maps, the ROIs are in block dots and positive connections are in red and negative connections are in blue. The thickness of the line is determined by the connectivity strength.

FIGURE 4

Shows significantly increased connectivity between the right thalamus and right DLPFC for 5 < 25 cm/s.

FIGURE 5

Shows significantly increased connectivity between the right SII and the right PPC for 5 cm/s > “All ON” and significantly increased connectivity between the right thalamus and the bilateral SII for 65 cm/s > “All ON”.

FIGURE 6

Shows the left SI (green sphere) and the left SII seeds (green sphere) overlaid on a standardized three-dimensional template and the significant seed-to-voxel results were presented on the right.

FIGURE 7

Shows the right SI (green sphere) and the right SII seeds (green sphere) overlaid on a standardized three-dimensional template and the significant seed-to-voxel results were presented on the right.