Towards Detailed Cortical Maps of the Human Back with Representational Similarity Analysis

BackgroundCortical 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.MethodsIn 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.ResultsFor 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.ConclusionsfMRI 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.FundingPrimary funding (as part of a project grant to MLM): Swiss National Science Foundation, Bern, Switzerland (ID 320030 185123).