Modification of the Site of Paralysis in Experimental Poliomyelitis. ∗

Abstract

Römer 1 noted that monkeys inoculated intraeranially with poliomyelitis virus frequently showed paralysis on the opposite side of the body. This suggested the participation of some decussating pathway in the propagation of the virus, but threw no light on the actual mechanisms which might be thus involved. A demonstration that virus may be routed along known fiber tracts in the central nervous system would go far toward explaining the fact that although the infective agent may enter through the olfactory tract, it usually traverses the entire brain stem without causing serious damage above the cord. Various cytologically distinct areas of the cerebral cortex provide the ideal conditions for such an experiment since their fiber connections with lower centers are sufficiently well known to provide a ready interpretation of the results obtained.

Accordingly 3 representative cortical areas were selected as sites for the introduction of the virus. The first, the so-called motor cortex, known cytologically as area 4 of Brodmann, was chosen because its known lower connections both ascending and descending are predominantly crossed. Next, the visual cortex, area 17 of Brodmann, presented the picture of an area with uncrossed connections. Its relations are with the lateral geniculate body of the same side, a region receiving the optic tracts, but possessing no direct connections with the lower brain stem or cord. The third region selected was the pre-motor cortex, or area 6 of Brodmann. The course of the fibers connecting this field with lower centers is not so well known as in the case of the other cortical areas. It is certain that its descending fibers run outside the pyramidal tract, proceeding as far as the midbrain and pons. 2 Stimulation of area 6 with the cortico-spinal tract eliminated 3 indicates that it is primarily concerned with movements of both arms, although there is a preponderance of crossed representation.