Preservation of Vision by the Pulvinar following Early-Life Primary Visual Cortex Lesions

Abstract

These findings suggest that sustained visual input through the pulvinar to MT following a lesion of V1 in early life has the capacity to afford improved visual outcomes.

Blindsight: Post-natal Potential of a Transient Pulvinar Pathway

“…As a later step in this proposed evolution, V1 projections to MT emerged slightly later in development, reducing or eliminating the role of the retinal inputs to PIm in vision, with PIm eventually becoming a satellite nucleus of MT, receiving its major input from MT while projecting back to MT. Thus, the results of Warner et al [9] provide insights into the ways in which area MT and surrounding cortex might have evolved in the immediate ancestors of primates.…”

“…The reasons why more vision is preserved in monkeys and humans with lesions of V1 in the developing brain have been unclear, but early lesions may result in faster and more complete degeneration of some structures and pathways, the enhancement of others, and the formation of new pathways [6]. A paper by Warner et al [9] in this issue of Current Biology presents multiple types of evidence that a small nucleus in the inferior pulvinar plays a central role in the greater preservation of cortical vision after V1 lesions in developing, compared to mature, primates.…”

“…Warner et al [9] demonstrate that, after early removal of V1 in marmosets (small monkeys), projections of the retina to PIm, and of PIm to MT are enhanced, leading to more direct and more effective activation of area MT ( Figure 1) by the pulvinar and better cortical vision than adults with V1 lesions. As area MT distributes information mainly to the dorsal stream of visual cortical processing [10], this could explain why visual guidance for reaching, locomotion, and other actions is better preserved after V1 lesions than conscious perception.…”

“…However, the preserved and enlarged projection from the retina to IPm, and then to area MT, after early V1 lesions in marmosets [9] certainly could account for the greater responsiveness of MT neurons after early lesions of V1 [18]. This retinal projection is normally reduced or lost in development [9], and thus it has been seldom described. This leaves the intriguing question; what is the normal function of a retina to PIm to MT pathway that is reduced or even lost in development.…”

“…Warner et al[9] propose that the early developing pathway of the retina to the medial nucleus of the inferior pulvinar (PIm) of primates activates the middle temporal visual area, MT, but this source of activation regresses and it is replaced by direct and indirect inputs from primary visual cortex, V1. When V1 is ablated early in postnatal development, major activating inputs from the retina via PIm are preserved and strengthened, thereby mediating more functional vision than occurs in primates with V1 lesions as adults.…”