Organization of the fibers in the dorsolateral funiculus of the cervical spinal cord in the cat

To investigate the functional organization in the lateral corticospinal tract (LCST), the cervical white matter was stimulated with multiple penetrations in the mediolateral direction at the C5/C6 and C6/C7 segmental borders in cats. Silicon substrate microelectrodes (CNCT, University of Michigan) with a linear arrangement of activated iridium contacts were used. The stimulation current consisted of a short (10-20 ms) train of charge balanced biphasic pulses at 330 Hz. The evoked limb movements were observed and the activities from selected forelimb muscles were acquired into a computer. Only the data points with an activation threshold of less than 30 μA were considered in the analysis. The muscle contractions were usually in the form of short twitches. Sustained muscle forces were observed only rarely for certain movements such as elbow flexion and digit extension in the forelimb. There exits a region in the middle of the dorsolateral funiculus for both segments where the activation threshold was relatively high (>30 μA). A segregation of the fibers according to the muscles they innervate was not found in these segmental borders. A functional organization is being investigated with further analysis.