Functional mapping of sensorimotor activation in the human thalamus at 9.4 Tesla

The thalamus, a central relay for sensory and motor signals in the brain, is still under investigation for its specific role in human sensorimotor processing. Given the small, centrally located nuclei in the thalamus, high-resolution imaging is crucial. This study uses ultra-high field fMRI (≥ 7 Tesla) to improve the signal-to-noise ratio, allowing the measurement of functional responses in individual thalamic nuclei.
A combination of motor (finger movement) and sensory (tactile) stimulation was used to enable localisation of individual nuclei. All measurements were performed at a 9.4 Tesla system using a custom-built 16-channel transmitter and a 32-channel receiver head coil. Functional images from ten subjects were acquired with a multiband EPI whole-brain sequence (86 slices, 1.25 x 1.25 x 1.25 mm3). Whole-brain T1w MPRAGE structural data sets were collected on a 9.4T, and at a Siemens Prisma 3T scanner with a 64-channel head coil.
At the individual level, significant bilateral activations were observed in different thalamic nuclei for motor and tactile tasks. The group of lateral nuclei (VPL, VA, VLa and VLp) as well as the group of pulvinar nuclei (PuA, PuM and PuL) showed increased BOLD signals during both tasks, supporting previous research. Interestingly, finger tapping elicited a more pronounced BOLD response compared to tactile stimuli. Furthermore, finger tapping also group of intralaminar nuclei (CM and Pf) known to be involved in attentional and motor processing. The thresholded t-maps for representative subjects, showing the activations during motor and tactile tasks, are shown in Figure 1.
To our knowledge, the present study is the first to identify sensorimotor thalamic nuclei in humans using task-based 9.4T fMRI. Our data provide new insights into understanding the function of individual thalamic nuclei in processing different input signals and confirm the advantages of using ultra-high field MR scanners for functional imaging of fine-scale, deeep brain structures.

Figure 1. T-Maps from the GLM analysis of the motor tasks and the tactile tasks. The t-contrast maps (p<0.001 unc., and 5-voxel minimum cluster size) for four subjects (S1, S3, S5 and S6) are overlaid on representative axial (top) and coronal (bottom) sections of the individual T1-weighted MPRAGE image (3T). The contours of the segmented thalamic nuclei (right panel) are shown for one subject (S6) mapped to the anatomical MPRAGE image.

Figure 1. T-Maps from the GLM analysis of the motor tasks and the tactile tasks. The t-contrast maps (p<0.001 unc., and 5-voxel minimum cluster size) for four subjects (S1, S3, S5 and S6) are overlaid on representative axial (top) and coronal (bottom) sections of the individual T1-weighted MPRAGE image (3T). The contours of the segmented thalamic nuclei (right panel) are shown for one subject (S6) mapped to the anatomical MPRAGE image.

Charyasz, E.; Heule, R.; Molla, F.; Erb, M.; Kumar, V.; Grodd, W.; Scheffler, K.; Bause, J.:

Functional mapping of sensorimotor activation in the human thalamus at 9.4 Tesla.

Frontiers in Neuroscience 17, 1116002 (2023)