Visualization of neural activities in lumbar spine in response to the sciatic nerve stimulation by magnetoneurography

Since the magnetic field is not affected by the surrounding bone and soft tissue, magnetoneurography (MNG) has been attracting attention as a new accurate electrophysiological examination of neural activities. We had developed MNG systems using SQUID magnetometers and had reported MNG of the cauda equina after the peroneal and tibial nerve stimulations. However, the magnetic signal intensity was not enough to diagnosing conduction block lesions in patients. In this study, we aimed to obtain strong signals from neural activities in lumbar spine using sciatic nerve stimulation and examine possibility in MNG. Neuromagnetic fields over lumbar area of five healthy volunteers were measured with MNG system after the sciatic nerve stimulation at the popliteal fossa. To confirm the supramaximal stimulation was performed during measurements, compound muscle action potential of extensor digitorum brevis muscle and abductor hallucis muscle were monitored. Current distributions around lumbar spine were calculated using spatial filter methods and superimposed on X-ray images. For comparison, neuromagnetic fields after peroneal stimulation at the fibula head and tibial nerve stimulation at the ankle were also measured. In all subjects, current distributions of neural activities were visualized and propagated in the spinal canal. Peak intensity of calculated currents at L4 spinal canal level was 2.7 times and 9.7 times stronger than that of peroneal and tibial nerve stimulation respectively. Using the sciatic nerve stimulation, we obtained sufficiently large signals and detailed current distribution. MNG is expected to contribute to the clinical diagnosis and treatment of lumbar spinal disease.