The organization of neocortical projections from the ventrolateral thalamic nucleus in the brush-tailed possum, Trichosurus vulpecula, and the problem of motor and somatic sensory convergence within the mammalian brain.

The retrograde transport of HRP was used to determine the extent and organizational details of the VL neocortical projection in Trichosurus. The major, or external, part of VL projects homotypically to the anteromedial part of the parietofrontal cortex, overlapping the VP cortical projection field extensively, but not completely. Overlap between the VL field and SmI is most extensive in the area of rear limb representation, and decreases considerably in the area of the head representation. A small internal subdivision of VL projects discontinuously to the SmI head region, and appears to be limited to portions of the cortical barrel field. The VL cortical projection is much less extensive than that of VP, but does include a small area of cortex which does not receive a VP projection. Thus VL and VP do not display congruent cortical projections. Details of the thalamocortical relationships, as determined from both anatomical and physiological studies, are compared with other mammals.