Identifying cortical columns for slow/rapid vibrotactile stimulation in human S1 using 7T fMRI.

2535 

Abstract Submission 

Ashley York¹, Harriet Dempsey-Jones², Thomas Shaw³, Alexander Puckett², Markus Barth⁴, Ross Cunnington²

¹Centre for Advanced Imaging, University of Queensland, Brisbane, Queensland, ²School of Psychology, University of Queensland, Brisbane, Queensland, ³Centre for Advanced Imaging, The University of Queensland, Brisbane, Queensland, ⁴Centre for Advanced Imaging, The University of Queensland, Brisbane, Australia

Ashley York, MPhil  
Centre for Advanced Imaging, University of Queensland
Brisbane, Queensland

Harriet Dempsey-Jones, PhD  
School of Psychology, University of Queensland
Brisbane, Queensland

Thomas Shaw, PhD  
Centre for Advanced Imaging, The University of Queensland
Brisbane, Queensland

Alexander Puckett  
School of Psychology, University of Queensland
Brisbane, Queensland

Markus Barth  
Centre for Advanced Imaging, The University of Queensland
Brisbane, Australia

Ross Cunnington, PhD  
School of Psychology, University of Queensland
Brisbane, Queensland

Cortical columns are functionally distinct units of the cerebral cortex that are organized perpendicular to cortical layers and typically process similar types of information (e.g., orientation preference). The extensive identification of cortical columns across the cortex has led some to propose that columnar organization might be a fundamental principle of the entire neocortex. However, evidence for such columnar organization in the human primary somatosensory cortex (S1) remains limited (see [1, 2]).

Columnar organization presumed to relate to slowly adapting (SA) and rapidly adapting (RA) receptors, has been identified in primate SI [3,4]. Recent studies, however, suggest that S1 neurons are organized by feature selectivity (e.g., shape, movement, vibration) rather than strictly by receptor type [5]. Despite this, there may still be columnar organization in human S1 related to processing specific frequencies, such as 3Hz (SA, intermittent pressure) and 30Hz (RA, vibration), which merits further research [6].

Here, we seek to adapt approaches proven effective in identifying visual columns (e.g., ocular dominance) using UHF fMRI to probe for SI columnarity.

To specifically target separate bands of functionally dissociable cortex (based on feature or receptor preference) vibrotactile stimulation was administered at frequencies of 3 and 30Hz, to the distal fingertips of the right hand. Trials of 3/30Hz were interleaved with a short inter-trial interval for 6 runs (~62mins). In a separate session, somatotopic fingertip regions were localized through phase-encoded fingertip mapping.

Data acquisition for 8 participants was conducted using 7T MRI (Fig.1). Anatomical images were captured with MP2RAGE (0.75mm iso), and functional data were obtained using a 3D-EPI sequence [7] (0.8mm iso, TR=1.92s) tilted to cover left S1. The surface-based analysis pipeline is detailed in Fig. 1. We analysed response delays from phasic fingertip stimulation, manually defining subject-specific regions of interest (ROIs) post-thresholding (FDR < 0.05; Fig2a). Within these ROIs, we used a general linear model (GLM) with motion and control regressors for deconvolution, conducting a general linear test (GLT) to compare responses to 3Hz and 30Hz stimulations.

We identified modular clusters in SI responding preferentially to 3Hz or 30Hz, suggestive of columnar organization (Fig.2b,c). We next binarized the GLT beta weights, and designated each vertex as 3/30Hz preferring. We assessed spatial consistency of these vibration preferences within sessions by comparing odd and even runs using a Jaccard index (0-1 scale; Fig.3a,b). We found the patterns were reliable, with ~64% vertices consistent across odd versus even runs. Furthermore, each of the observed Jaccard indices significantly exceeded the chance level established by a random-permutation null model, indicating a robust effect size (Fig.3b).

For one participant, we collected an additional 12 runs of data in a separate session. Fig 3a shows the odd/even intersection map (vertices with the same signed beta-weight in odd/even runs), as well as the preference of each vertex for 3/30Hz within the mask. This analysis further supported the spatial consistency of 3/30Hz vertex preference. While column sizes appeared similar along the anterior bank and crown of the postcentral gyrus, the posterior bank showed a predominance of vertices preferring 3Hz. This pattern aligns with previous research suggesting an increase in receptive field size along the anterior to posterior axis of the postcentral gyrus.

While columnar organisation was first identified in SI animal models [8], there has since been limited evidence reported in humans [1,2]. We found clear, reliable patterns of modular clusters responsive to different vibrotactile frequencies. Our results broaden our understanding of cortical organisation principles in sensory cortex, supporting the idea that this structure might be present in all sensory areas.

Cortical Anatomy and Brain Mapping ²

Perception: Tactile/Somatosensory ¹

Cortical Columns

Somatosensory