Often mislabeled as a simple relay of sensory information, the thalamus is a complicated structure with diverse functions. This diversity is exemplified by roles visual thalamus plays in processing and transmitting light-derived stimuli. Such light-derived signals are transmitted to the thalamus by retinal ganglion cells (RGCs), the sole projection neurons of the retina. Axons from RGCs innervate more than ten distinct nuclei within thalamus, including those of the lateral geniculate complex. Nuclei within the lateral geniculate complex of nocturnal rodents, which include the dorsal lateral geniculate nucleus (dLGN), ventral lateral geniculate nucleus (vLGN), and intergeniculate leaflet (IGL), are each densely innervated by retinal projections, yet, exhibit distinct cytoarchitecture and connectivity. These features suggest that each nucleus within this complex plays a unique role in processing and transmitting light-derived signals. Here, we review the diverse cytoarchitecture and connectivity of these nuclei in nocturnal rodents, in an effort to highlight roles for dLGN in vision and for vLGN and IGL in visuomotor, vestibular, ocular, and circadian function.

The work of Mircea Steriade demonstrated that the neocortex could synchronize large regions of the thalamus within 10−100 msec. Unlike the synchrony generated by the cortex, the retinal afferents synchronize a restricted group of neighboring thalamic neurons with <1-msec precision. Here, we use a large sample (n = 372) of simultaneous recordings from neighboring neurons in the lateral geniculate nucleus (LGN) to illustrate the high specificity of the synchrony generated by retinal afferents and its dependency on sensory stimulation. First, we demonstrate that cells sharing a retinal afferent show a balanced receptive field diversity: although slight receptive field mismatches are common, the largest mismatches in a specific property (e.g. receptive field size) are restricted to cells that are precisely matched in other properties (e.g. receptive field overlap). Second, we show that these receptive field mismatches are functionally important and can lead to a 5-fold variation in the percentage of synchronous spikes driven by the shared retinal afferent under different stimulus conditions. Based on these and other findings, we speculate that the precise synchronous firing of cells sharing a retinal afferent might serve to amplify local stimuli that might be too brief and small to generate a large number of thalamic spikes.

Cells of the cat's perigeniculate nucleus (PGN), part of the visual sector of the thalamic reticular nucleus (TRN), provide GABAergic inhibition to the A and A1 layers of the dorsal lateral geniculate nucleus (LGNd) and, therefore, may control information flow from the retina to the cortex. Previous electrophysiological experiments suggested that the PGN may be subdivided on the basis of ocular dominance thus reflecting the afferent and efferent projections with lamina A and A1 of the LGNd. The present study utilized the ability of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) to be transported transneuronally following intraocular injections in four cats to examine whether there is any anatomical evidence for eye specific layers within the PGN. Sections were processed with tetramethylbenzidine. Light WGA-HRP transneuronal labeling of LGNd collaterals and somata were seen in the PGN and very light labeling (but not somata) was seen in the TRN. Neither the cells of the PGN projecting to the LGNd nor the LGNd relay collaterals within the PGN were clearly organized into nonoverlapping laminae related to the eye specific layers of the LGNd. However, parts of the PGN immediately adjacent to the LGNd appear devoid of connections with lamina A1 thus creating a thin monocular segment for the contralateral eye.