SITE OF CORTICAL UTRICULAR REPRESENTATION WITH SPECIAL REFERENCE TO THE SOMATOSENSORY BARREL FIELD IN THE GERBIL

In mammals, the osseous semicircular canals of the vestibular labyrint hs are usually embedded in the pyramis of the temporal bone. Thus, the osseous semicircular canals are a cavity system that can only be visu alized by injection molding. Exceptionally, the walls of the osseous s emicircular canals of the Mongolian gerbil are not embedded, but expos ed in the hollow space in the temporal bone. Under urethane anesthesia , a window was made in the periotic capsule of the gerbil to reach thi s hollow space (semicircular canal triangle), and a pair of wire elect rodes were inserted through an opening made in the horizontal semicirc ular canal toward the utricular nerve endings. Repetitive electric sti muli at 80 Hz were applied, and the direction of eye movements was not ed. Subsequently, the stimulation frequency was reduced to 0.3 Hz, and evoked potentials were recorded from the neocortex. Positive surface potentials and negative deep potentials were recorded in the somatosen sory area and, more specifically, in the vibrissa ''barrel field,'' as judged by later histochemical staining of the cortical specimens. Thi s unique anatomic feature of the gerbil labyrinth offers an opportunit y whereby the Vestibular organ can be reached without any heavy surgic al insult, and the presence of fine-grain vibrissa barrels in this spe cies (seven rows instead of five rows in most rodents) will help eluci date functional interactions between vestibular and somatosensory sens ations.