Hidden Vision and Beyond: Multiscale Foundations of Thalamic Organization

The subcortical visual system is traditionally described through a small number of canonical pathways, with the dorsal lateral geniculate nucleus (LGN) viewed primarily as a first-order relay to primary visual cortex and additional routes through the superior colliculus, pulvinar and koniocellular LGN considered secondary or residual. Here, we review recent evidence across species, methods, and scales that challenge this framework and suggest that the visual thalamus is an active, dynamically regulated component of visual processing. We first consider primary and nonprimary visual pathways, showing how thalamic inputs shape cortical responses through the timing, spatial arrangement, synaptic organization, laminar targeting, and circuit-level integration of feedforward signals. We then reconsider the "first-order" status of LGN itself, reviewing evidence that nonretinal subcortical inputs, local inhibition, and corticothalamic feedback can alter LGN responses and the signals routed onward to cortex. This shifts the view of LGN from a passive relay supplying a dynamic cortex to a dynamically regulated node in its own right. Next, we review advances in higher-order thalamic organization, highlighting structured thalamocortical connectivity, network-level coordination, and state-dependent dynamics. Finally, we consider how thalamic functions change in the injured brain, where emerging models disentangle acute effects of damage from chronic compensation to reveal how surviving thalamic and downstream pathways may be remodeled, reweighted, or recruited to support residual visual function and recovery. Together, these findings support a multiscale view of the thalamus as a collection of specialized, adaptive nuclei embedded within distributed cortico-subcortical networks, with implications for perception, cognition, sensory disorders, and rehabilitation.