STUDIES ON THE HUMAN EVOKED ELECTROSPINOGRAM

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.     

STUDIES ON the HUMAN EVOKED ELECTROSPINOGRAM

Evoked potentials from the human spinal cord were studied in 39 normal volunteers. Intrathecal recordings from lower cervical and lower thoracic intervertebral levels were made after the supramaximal stimulation of the median, ulnar and posterior tibial nerves, respectively. It was shown that the segmental cord potentials varied in shape and size according to the spatial relationship between the position of the electrode tip and the spinal cord and roots within the vertebral canal. Three main types of segmental evoked responses were obtained. One of them was recorded behind the cord dorsum and around the midline, and was composed of fast, sharp early, and slow, late components. This was called a CD potential and its first component was related to the activity of the ascending dorsal funiculus fibres. The second evoked response was the DR potential, and this triphasic compound action potential of very high amplitude and longer duration had no remarkable late component. It was recorded when the tip of the intrathecal electrode was lateral to the midline within the vertebral canal, and was then related mostly to activity of the spinal roots. Another kind of potential was called PH potential. It had a very small triphasic spike and two later components with prominent negativities being higher than the first spike. This potential might be related to the electrode tip position facing, and close to, the posterior horn of the spinal gray matter. Late components of the segmental evoked potentials were related to the pre- and post synaptic activity of the horizontally oriented fibre within the segmental gray matter of the posterior horn.