New view of the organization of the pulvinar nucleus in Tupaia as revealed by tectopulvinar and pulvinar‐cortical projections

Abstract

The projections of the superficial layers of the superior colliculus to the pulvinar nucleus in Tupaia were reexamined by injecting WGA-HRP into the tectum. The main result was finding two different patterns of terminations in the pulvinar nucleus: a zone remote from the lateral geniculate nucleus, which occupies the dorsomedial and caudal poles of the pulvinar nucleus, was almost entirely filled with terminals in every case irrespective of the location of the injection site; and a second division of the pulvinar nucleus, adjacent to the lateral geniculate nucleus, contained irregular patches--much more densely populated--and the distribution of patches varied from case to case. We call the first projection "diffuse" and the patchy projection "specific." Next we injected several divisions of the extrastriate visual cortex to find the cortical target of each pathway. The diffuse path terminates in the ventral temporal area (Tv). The specific path terminates in the dorsal temporal area (Td) and area 18. We speculated about the significance of the two pathways: the specific path may be responsible for the preservation of vision after removal of the striate cortex; the diffuse path may have an important place in the evolution of the visual areas of the temporal and occipital lobe. We argued that the target of the diffuse path is in a position to relate limbic and visual impulses and relay the product of such integration to the other visual areas, striate as well as extrastriate cortex.

Signal processing in the tectothalamic pathway.

“…Both sets of experiments indicate that the caudal pulvinar nucleus is connected with more rostral regions of the temporal cortex, whereas the rostral pulvinar connects to more caudal regions of the temporal cortex. These results corroborate the findings of Luppino et al (1988), who described the distribution of pulvinar cells labeled by retrograde transport following injections in dorsal (Td) and ventral (Tv) subdivisions of the tree shrew temporal cortex, as well as Diamond et al (1970) and who described the distribution of degenerating thalamocortical cells and terminals following cortical or thalamic lesions respectively.…”

“…The tectal projections to these 2 subdivisions are organized differently; those to Pd terminate diffusely, whereas those to Pc terminate in a more spatially precise manner (Luppino et al 1988). In subsequent studies usmg anterograde and retrograde tracing techniques, as well as electron microscopy, we concluded further that although both Pd and Pc receive topographically organized projections from the SC, the Pd receives additional diffuse projections, which possibly arise from wide-ranging axon collaterals of tectopulvinar cells ).…”

Morphological comparison of visual pathway projections to the temporal lobe from cortical area VI and the tectorecipient zone of the pulvinar nucleus in the tree shrew (Tupaia belangeri).

“…Projections from PC (Lyon et al 2003;Luppino et al 1988) and PD (Luppino et al 1988) to V2 have been previously reported. These two studies used retrograde tracer injections in V2 to identify cell bodies in the thalamus that project to V2.…”

“…None of our anterograde injections in the pulvinar nucleus regions PC and PD projected to V2. In reviewing those studies, the lack of PD to V2 projections in the more recent study by Lyon et al (2003) may indicate that the injections by Luppino et al (1988) overran the boundary of V2 to TP (Luppino et al 1998 figure 8) and V2 to TD (Luppino et al 1998 figure 9), so that the cell bodies found in PD came from TP and I or caudal TD.…”

Substance P and the tectothalamic pathway.

“…Luppino et al (1988) first described these projections as "diffuse" and "specific" respectively. By using a combination of anterograde and retrograde tracing techniques, as well as electron microscopy, we concluded that both the Pd and Pc receive topographic (specific)…”