BONY FORAMINA FACILITATE MAGNETIC STIMULATION - AN EXPERIMENTAL CAT SCIATIC-NERVE MODEL

We have established an experimental bony foramen model in vivo using a cat sciatic nerve, a section of skull bone and a column made from met hylmethacrylate. In each model, a foramen-like slit or fissure was cre ated. Motor responses of the cat right gastrocnemius were elicited wit h a figure-of-8-shaped magnetic coil. Very high intensities of magneti c stimulation were necessary to evoke motor responses with the coil pl aced on the thigh. However, when the bone section or methylmethacrylat e column was placed under the thigh muscle layer with the sciatic nerv e fitted into the foramen-like slit or fissure, motor responses could be elicited with a smaller intensity of magnetic stimulation. Despite changes in stimulation intensity or shifts in the magnetic coil, the l atency of the motor responses remained constant. By comparing the late ncy with the electrical recording, the site of excitation was predicte d to be at the exit of the foramen. Our studies have confirmed that bo ny structures, especially bony foramina, facilitate excitation of the nerve by magnetic stimulation and that the exit of the foramen could b e the preferential site for magnetic stimulation. (C) 1997 Elsevier Sc ience Ireland Ltd.