Studies on the human evoked electrospinogram. II. The conduction velocity along the dorsal funiculus

The propagation velocity of the ascending volleys along the dorsal funiculus of the human spinal cord was studied in 31 normal volunteers. Intrathecal recordings from lower cervical and lower thoracic intervertebral levels were made after the supramaximal stimulation of the posterior tibial nerves. When the electrode tip was behind the cord dorsum at the cervical level, it was easily possible to obtain very clear triphasic compound action potential on stimulation of the posterior tibial nerve of one leg or both legs. This "Tractus Potential" was found to originate mainly from the dorsal funiculus fibres, i.e. Fasciculus gracilis. The maximal conduction velocity of the ascending afferent volley from the leg was then calculated to be, on average, 37 meters/sec between lumbar and cervical spinal enlargements. Intrathecal stimulation and recording of the spinal cord gave the distinct triphasic wave with low threshold. This was also found to be related to dorsal funiculus activity. In these intraspinal stimulations and recordings, very early small and some late long-lasting deflections appeared, especially in the lateral position of the intrathecal electrode.