In the back of your mind: Cortical mapping of paraspinal afferent inputs

• Published in: Human brain mapping 2022-11, Vol.43 (16), p.4943-4953
• Main Authors: Cole, David M., Stämpfli, Philipp, Gandia, Robert, Schibli, Louis, Gantner, Sandro, Schuetz, Philipp, Meier, Michael L.
• Format: Article
• Language: English
• Subjects: back; Body parts; Brain mapping; Brain Mapping - methods; Brodmann's area; Compressed air; cortex; Cortex (motor); Extremities; Fingers; fMRI; Functional magnetic resonance imaging; Hand - physiology; Humans; Low back pain; Magnetic resonance imaging; Magnetic Resonance Imaging - methods; Mapping; Medical imaging; motor control; Neuroimaging; Neuromuscular diseases; Neuroplasticity; proprioception; Representations; Scanners; Sensory neurons; somatosensory; Somatosensory cortex; Somatosensory Cortex - diagnostic imaging; Somatosensory Cortex - physiology; somatotopy; Stimulation; Tactile stimuli; Thorax; Topography; Vertebrates; Vibrations
• ISSN: 1065-9471; 1097-0193
• DOI: 10.1002/hbm.26052

Topographic organisation is a hallmark of vertebrate cortex architecture, characterised by ordered projections of the body's sensory surfaces onto brain systems. High‐resolution functional magnetic resonance imaging (fMRI) has proven itself as a valuable tool to investigate the cortical landscape and its (mal‐)adaptive plasticity with respect to various body part representations, in particular extremities such as the hand and fingers. Less is known, however, about the cortical representation of the human back. We therefore validated a novel, MRI‐compatible method of mapping cortical representations of sensory afferents of the back, using vibrotactile stimulation at varying frequencies and paraspinal locations, in conjunction with fMRI. We expected high‐frequency stimulation to be associated with differential neuronal activity in the primary somatosensory cortex (S1) compared with low‐frequency stimulation and that somatosensory representations would differ across the thoracolumbar axis. We found significant differences between neural representations of high‐frequency and low‐frequency stimulation and between representations of thoracic and lumbar paraspinal locations, in several bilateral S1 sub‐regions, and in regions of the primary motor cortex (M1). High‐frequency stimulation preferentially activated Brodmann Area (BA) regions BA3a and BA4p, whereas low‐frequency stimulation was more encoded in BA3b and BA4a. Moreover, we found clear topographic differences in S1 for representations of the upper and lower back during high‐frequency stimulation. We present the first neurobiological validation of a method for establishing detailed cortical maps of the human back, which might serve as a novel tool to evaluate the pathological significance of neuroplastic changes in clinical conditions such as chronic low back pain. Systematic investigations of cortical representations of somatosensory paraspinal afferents along the thoracolumbar axis are lacking. Using functional magnetic resonance imaging combined with a novel vibrotactile stimulation device for the back, we found distinct sensorimotor cortical representations of different types of paraspinal stimulation, as well as clear topographic differences between the upper and lower back. Findings could be important in elucidating the role of cortical reorganisation in the pathophysiology of chronic lower back pain.