Estimation of localization of neural activity in the spinal cord using a biomagnetometer.

Spinal cord evoked potentials (SCEPs) measurement is widely used for level diagnosis of spondylotic myelopathy. However, because of the restriction of spatial resolution, SCEPs do not distinguish the neurophysiological activities among tracts in the spinal cord without invasive methods. Magnetic field measurement has the theoretical advantage of high spatial resolution, compared with electric measurement. We recorded spinal cord evoked magnetic fields (SCEFs) in the thoracic spinal cord after stimulation to the motor area in felines, and estimated the source of the magnetic fields. SCEFs showed a quadrupolar pattern, and conducted in a cranial-to-caudal direction at 55 m/sec. According to this result, we estimated that the SCEFs after stimulation to the motor area were generated by the contralateral corticospinal tract. Furthermore, the estimated dipole of the SCEFs after stimulation to the motor area was located on the contralateral side in the spinal cord. These results correspond with the anatomical location of the corticospinal tract of felines, and suggest that magnetic field recording can detect the magnetic source localization of each tract in the spinal cord.