Neural Circuit Analysis after Spinal Cord Injury

Objectives and Significance

After a spinal cord injury (SCI), a person often loses her/his ability to walk due to the blockage of the descending command from the brain. While medical treatments and rehabilitation to restore the walking ability have been extensively studied, there are other disabilities that result from an SCI. Malfunctioning of the lower urinary tract system is one such example of significant importance for maintaining the quality of life. For instance, urinary incontinence may result after an SCI at a sacral level, and detrusor-sphincter dyssynergia (co-contraction of bladder and its opening) may occur after an SCI at a higher level. Thus, an SCI patient often suffers from difficulty of either holding or voiding, or both.

The micturition is mainly controlled by autonomic neuronal circuits in the lumbosacral spinal cord. The holding reflex is largely self-contained in the circuits and is autonomous, while the voiding reflex is regulated by descending signals from the upper level of the spinal cord and brain. After an SCI, the proper functioning of the micturition system is lost due to the blockage of the descending signal and/or some reflex pathways. Recent studies show some effectiveness of noninvasive treatments by electrical or magnetic stimulation applied to the spinal cord for neural rehabilitation to restore the micturition capability. However, the outcome depends on the individuals, and the restored capability tends to be lost once the treatment sessions are terminated.

This research develops a mathematical model of the micturition circuits and characterize the effect of electro-magnetic stimulation on the spinal cord after injury. We aim to uncover the mechanisms underlying urinary incontinence and detrusor-sphincter dyssynergia as dynamical phenomena resulting from feedback interactions of neuromechanical elements. We will also examine how spinal stimulation acts as the control input to the micturition circuits and alters their behavior with acute and chronic effects. Such understanding will enable us to associate an SCI at a particular level/site with specific symptoms, and suggest effective pattern (frequency, temporal shape, spatial location) of stimulation for neural rehabilitation.