A comparison of the organization of the projections of the dorsal lateral geniculate nucleus, the inferior pulvinar and adjacent lateral pulvinar to primary visual cortex (area 17) in the macaque monkey
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Abstract
Both anterograde and retrograde transport tracing methods were used to study the organization
of the projections of the dorsal lateral geniculate (DLG), the inferior pulvinar and
subdivisions of the lateral pulvinar to primary visual cortex (striate cortex or area
17). The DLG projects only to striate cortex. These projections are retinotopically
organized, and do not extend to any cortical layers above layer IVA. In contrast the
inferior pulvinar (PI) and the immediately adjacent portion of the lateral pulvinar
(PL alpha 48) project to both striate and prestriate cortex. The projections from
these two thalamic areas to the striate cortex are also retinotopically organized
and exist in parallel with those from the DLG. In contrast to the DLG, the projections
from PI and PL alpha terminate above layer IVA in striate cortex, i.e. layers I, II
and III. In prestriate cortex the layers of termination include layers IV, III and
I. The pulvinar terminations in layers II and III of area 17 occur in segregated patches
as do the geniculate terminations in layers IVC and IVA. On the other hand the pulvinar
terminations in layer I which overlie those in layers II and III of area 17 appeared
to be continuous. Control studies show that the remainder of the lateral pulvinar
overlying PL alpha does not project to striate cortex. It is concluded that there
are 3 visuotopically organized inputs from the lateral thalamus to primary visual
cortex and that each of these inputs have different layers of termination. The inputs
from PI and DLG can convey direct retinal inputs while those from PI and PL alpha
can also be involved in intrinsic cortico-thalamocortical connection with prestriate
cortex. It remains, then that it cannot be tacitly assumed that the ascending inputs
which influence the response properties of the primary cortical neurons arise solely
from the dorsal lateral geniculate nucleus. It is also argued that these inputs to
the supragranular layers may be excitatory as those from the DLG to the IVth layer.