<p>The objective of this study was to develop an MR-safe stimulation device (pneumatic vibration device, pneuVID) that can apply vibrotactile stimulation to different thoracolumbar segments and to characterize stimulation parameters such as the amplitude and its stability for two relevant frequencies (20Hz/80Hz). This is the first apparatus specifically designed for paraspinal tissue vibration on different segmental levels in an MR environment. </p>

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.

Persistent pain alters brain-body representations, highlighting their potential pathological significance. In chronic low back pain (LBP), sparse evidence points towards a shift of the cortical representation of sensory afferents of the back. However, systematic investigations of the cortical representation of tactile and proprioceptive paraspinal afferents along the thoracolumbar axis are lacking. Detailed cortical maps of paraspinal afferent input might be crucial to further explore potential relationships between brain changes and the development and maintenance of chronic LBP. We therefore validated a novel and functional magnetic resonance imaging- (fMRI-)compatible method of mapping cortical representations of tactile and proprioceptive afferents of the back, using pneumatic vibrotactile stimulation ("pneuVID") at varying frequencies and paraspinal locations, in conjunction with high-resolution fMRI. We hypothesised that: (i) high (80 Hz) frequency stimulation would lead to increased postural sway compared to low (20 Hz) stimulation, due to differential evoked mechanoreceptor contributions to postural control (proprioceptive vs tactile); and (ii) that high (80 Hz) versus low (20 Hz) frequency stimulation would be associated with neuronal activity in distinct primary somatosensory (S1) and motor (M1) cortical targets of tactile and proprioceptive afferents (N=15, healthy volunteers). Additionally, we expected neural representations to vary spatially along the thoracolumbar axis. We found significant differences between neural representations of low and high frequency stimulation and between representations of thoracic and lumbar paraspinal locations, in several bilateral sensorimotor cortical regions. Proprioceptive (80 Hz) stimulation preferentially activated sub-regions S1 3a and M1 4p, while tactile (20 Hz) stimulation was more encoded in S1 3b and M1 4a. Moreover, in S1, lower back proprioceptive stimulation activated dorsal-posterior representations, compared to ventral-anterior representations activated by upper back stimulation. As per our hypotheses, we found distinct sensorimotor cortical tactile and proprioceptive representations, with the latter displaying clear topographic differences between the upper and lower back. This thus represents the first behavioural and neurobiological validation of the novel pneuVID method for stimulating muscle spindles and mapping cortical representations of paraspinal afferents. Future investigations of detailed cortical maps will be of major importance in elucidating the role of cortical reorganization in the pathophysiology of chronic LBP.

<p>The objective of this study was to develop an MR-safe stimulation device (pneumatic vibration device, pneuVID) that can apply vibrotactile stimulation to different thoracolumbar segments and to characterize stimulation parameters such as the amplitude and its stability for two relevant frequencies (20Hz/80Hz). This is the first apparatus specifically designed for paraspinal tissue vibration on different segmental levels in an MR environment. </p>

Background: Cortical reorganization and its potential pathological significance is increasingly studied in chronic low back pain (CLBP) patients. Yet, detailed cortical maps of the healthy human back are lacking. To better understand cortical changes during the development and maintenance of CLBP, a detailed baseline characterization resulting from sensory thoracolumbar afferent input is needed. To this end, a novel pneumatic vibrotactile stimulation method was used to stimulate paraspinal sensory afferents while studying their cortical representations in unprecedented detail. Methods: In 30 young healthy participants, vibrotactile stimulations at 20Hz and 80Hz were applied bilaterally at nine locations along the thoracolumbar axis while functional magnetic resonance imaging (fMRI) was performed. A whole-brain searchlight representational similarity analysis (RSA) in combination with different experimental models of paraspinal afferent input was used to investigate the representational organization of the respective neuronal activation patterns. Results: For 80Hz, the organizational structure of the neuronal activation patterns yielded the best fit for a model based on segmental distances between the stimulated paraspinal locations, located bilaterally in the primary (S1) and secondary somatosensory (S2) cortices. For 20Hz, this observation was restricted to the right S1. Conclusions: fMRI during paraspinal vibrotactile stimulation in combination with RSA is a powerful tool that can be used to establish highly detailed cortical maps of the human back. The current findings constitute a promising basis to further explore cortical reorganization and its potential pathological meaning in CLBP patients.