Figure 2

Reconstructed currents of a healthy subject measured after stimulation of the lower thoracic spinal cord. (a) Reconstructed current map. Currents at the level of the spinal canal were reconstructed by a recursive null-steering (RENS) beamformer and superimposed on an X-ray image. Current intensity is shown by a colour scale (red is higher). Small white arrows indicate current vectors. The leading component of the currents (large upwards-pointing red arrow) appeared 4.3 ms after stimulation and propagated cranially along the spinal canal. At 5.8 ms, the trailing component (downwards-pointing red arrow) appeared from the caudal side. Perpendicular currents (blue arrows) flowing towards the spine between the leading and the trailing components are also observed on both sides. (b) Waveforms of reconstructed currents at the “virtual electrodes”. Red traces are currents at the midline of the cervical spinal canal (the caudal to cranial direction is upwards). Blue traces are currents 20 mm lateral from the midline (upwards is towards the spinal canal).