Cortical Representations of Vibrotactile Stimuli with Varying Frequency in Human S1

2534 

Abstract Submission 

Ji-Hyun Kim¹, Junsuk Kim², Sung-Phil Kim¹

¹UNIST, Ulsan, Ulsan, ²Kwangwoon University, Seoul, Seoul

Ji-Hyun Kim  
UNIST
Ulsan, Ulsan

Junsuk Kim  
Kwangwoon University
Seoul, Seoul

Sung-Phil Kim  
UNIST
Ulsan, Ulsan

Animal studies showed that tactile sensations from slowly adapting receptors (SA) and rapidly adapting receptors (RA) elicit different spatial activation patterns within the primary somatosensory cortex (S1) (Mountcatle, 1957; Sur et al., 1981), suggesting similar neural representations in human S1. Using 3T fMRI with conventional BOLD signals, however, it is limited to uncover the receptor-specific neural responses in human S1. Therefore, in this study, we employed advanced high-resolution (0.7mm) fMRI at 7T with VASO-BOLD sequence to investigate the laminar and columnar characteristics of neural responses to vibrotactile stimulations with varying frequencies in human S1 (Brodmann Area 3b).

Thirteen healthy volunteers (8 male, 26.94 ± 3.2 years old) participated in this study. All neuroimaging measurements were conducted using a 7T scanner (MAGNETOM Terra, Siemens Healthineers, Erlangen, Germany) with a single channel transmitter and a 32-channel receiver head coil (NOVA Medical, Wilmington, MA). We used a multi-contrast VASO-BOLD sequence (Lu et al., 2003) with slices aligned to the central sulcus between the motor and sensory cortices of the participants. The imaging parameters were as follows: 0.7-mm isotropic resolution, in-plane reduction factor (Rin-plane) = 3, field of view (FOV) = 154 × 154 mm2, 12 slices, and TI1/TI2 = 67.14/2390.9 ms. Seven different frequency stimuli were applied to the left index fingertip of the participants (ranging from 2 to 38 Hz in 6 Hz increments), generated by piezoelectric devices equipped with 6-mm diameter electrodes (Dancerdesign, St. Helens, UK). Each participant completed eight runs to obtain VASO and BOLD images. During each run, the seven vibrotactile stimuli were randomly presented twice, resulting in fourteen task trials. We localized the brain regions that specify participants' index finger and set the region of interest (ROI) to fit BA 3b in S1. For laminar analysis, thirteen equivolume layers were calculated across the cortical depth of BA 3b. We calculated the mean VASO signal change within the voxels that corresponded to individual layer. For columnar analysis, ROIs were unfolded into 2D and similarity in cortical response patterns across columns was measured, expecting distinct spatial distributions between SA and RA columns. The columnar similarity was quantified using cosine similarity between vectors representing column activations at different frequencies. Laminar and columnar analyses were conducted using the software LAYNII (https://github.com/layerfMRI/LAYNII).

We first confirmed that the vibrotactile stimuli activated BA 3b in contralateral S1. The laminar analysis showed that SA stimuli (2-Hz) elicited activation centered at the middle layer, while RA stimuli (38-Hz) elicited increasing activation towards the superficial layer. Other stimuli with intermediate frequencies between 8 Hz and 32 Hz resulted in activation patterns of both SA and RA, including activation in the middle-layer and increased activation towards the superficial layer. The columnar analysis revealed that responses of each column activated by 2-Hz and 38-Hz stimuli were the least similar to each other, indicating a distinct columnar distribution of cortical responses to SA and RA.

In this study, we reported that SA-, and RA-specific tactile stimuli elicited distinct spatial patterns of neural responses in human S1. Our finding in humans is in line with the previous report of peak activations in layer IV by SA stimulation in non-human primates (Mountcatle, 1957). Moreover, our results suggest spatial neural representations of vibrotactile frequency in S1 such that the superficial layer is more activated than the middle layer as the frequency increases. Our study may provide insights into the structural characteristics of S1 in processing the vibrotactile information.

Non-BOLD fMRI ²

Attention: Auditory/Tactile/Motor

Perception: Tactile/Somatosensory ¹

Cortex

Cortical Columns

Cortical Layers

FUNCTIONAL MRI

NORMAL HUMAN

Perception

RECEPTORS

Somatosensory

Touch