Human spinal cord activation during filling and emptying of the bladder

The spinal cord is essential for processing sensory information and regulating autonomic functions, such as bladder control, which is critical for urinary continence and voiding. Understanding how the spinal cord represents bladder pressure can provide valuable insights into the neural mechanisms underlying bladder control and contribute to developing better therapies for bladder dysfunction. However, measuring neural activity in the human spinal cord is notoriously challenging due to its small size and the surrounding bony and fascial enclosures, limiting the effectiveness of traditional neuroimaging techniques. Functional ultrasound imaging (fUSI) is a minimally invasive, emerging modality that overcomes these barriers, offering high sensitivity, spatial coverage, and spatiotemporal resolution for studying neural dynamics. Here, we combine fUSI with urodynamically controlled bladder filling and emptying to examine hemodynamic responses in the human spinal cord during one cycle of micturition. Using intravesical bladder pressure recordings, we identify spinal cord regions with hemodynamic signals that strongly correlate with bladder pressure. Furthermore, a linear support vector machine regression model (SVM-r) trained on the fUSI power Doppler signal reveals relevant spinal cord regions and accurately reconstructs bladder pressure changes. Our findings provide evidence of bladder pressure-responsive regions in the spinal cord, where hemodynamic signals strongly correlate with bladder pressure.