Projections from the lateral geniculate nucleus in the cat and monkey

686M. E. WILSON AND B. G. CRAGGcontain part of area 18 or 19 or both. It is, however, difficult to say whether theregions receiving the degenerated projection should be designated as area 18 or 19(see Discussion).In another cat, C 15, the lesion damaged mainly the pulvinar nucleus, with someinvolvement of the N. lateralis posterior and N. lateralis dorsalis, but did not touchthe LGN or its medial interlaminar nucleus. The cortical degeneration was confinedto the crown and lateral wall of the suprasylvian gyrus in the middle part of itsantero-lateral extent. The lateral gyrus was entirely free from degeneration (seeFig. 6).A lesion that extended most of the length of the N. lateralis posterior was made inanother cat (C 16) without involvement of other nuclei. No retrograde reaction wasseen in Nissl preparations in the LGN or pulvinar nucleus. Fibre degeneration wasfound only on the posterior ectosylvian and posterior suprasylvian gyri, and wasprobably due to track damage. Waller & Barris (1937) suggested that N. lateralisposterior projects to the anterior end of the suprasylvian gyrus. Unfortunately, thefrontal block was not stained. The results in C 16 do, however, exclude a projectionto the lateral gyrus from this source.Combined lesions of the LGN and more medial structuresIn the course of making the lesions described above, seven other brains (C 17-C23)were studied in which a lesion in the LGN had spread to involve more medial structuresincluding the medial interlaminar nucleus and the pulvinar nucleus. In onebrain (C 17) the lesion was just beneath the LGN, damaging the latter medially andinvolving the medial interlaminar nucleus, and part of the posterior nucleus, N.lateralis posterior and perhaps part of the pulvinar nucleus. Dense degeneration wasdistributed laterally across the lateral gyrus from its medial edge, but did not descendfar into the lateral wall of the gyrus. There was also some slight degeneration on themedial wall of the hemisphere especially at the bottom of the splenial sulcus, and inthe middle suprasylvian gyrus. In the other six cats the lesion involved the LGNdorso-medially, as well as the medial interlaminar nucleus and other medial structures.Two of these lesions were so far posterior that the degeneration in the cortexwas confined to the posterior block where it was mixed with degeneration due to theneedle track through the white matter. In the other four brains (C 18-C21) there wasdegeneration in the middle suprasylvian gyrus and in the lateral part of the lateralgyrus, and at the bottom of the splenial sulcus. Besides this constant finding, therewas degeneration in the crown of parts of the lateral gyrus corresponding to thevariable antero-posterior placement of the lesion in the LGN.Contra-lateral degenerationAll the fibre degeneration described above was ipsi-lateral with the lesion, and nocontra-lateral degeneration in the lateral gyrus was seen in any of the eleven brainswith lesions of the LGN (C 8-11, 17-23). The lesions confined to more medial structuresdid not cause contra-lateral degeneration either. The needle track was fine andavoided the corpus callosum (Fig. 1). The range of survival times covered the periodof 1-3 weeks specified by Glickstein, Miller & Smith (1964).