Development and evolution of thalamocortical interactions

Thalamocortical projections in mammals must travel through a considerable p ortion of the newly formed subdivisions of the embryonic forebrain. They de scend through the ventral thalamus, advance in the internal capsule amongst cells which already possess dorsal thalamic projections, traverse the stri atocortical junction, and then reach the cerebral cortex by associating wit h subplate cells and their early corticofugal fibers. The interactions of t he thalamocortical projections with early generated, largely transient cell s of these regions are believed to play a crucial role in their deployment. These ideas are supported by recent work on reeler and other strains of mu tant mice. While we are beginning to understand the basic pattern of the ce llular and molecular interactions employed in mammalian thalamocortical dev elopment, comparative developmental studies hold the promise to reveal the underlying logic of these steps and the evolutionary origin of the mammalia n cerebral cortex.