Patterns of retinal terminations and laminar organization of the lateral geniculate nucleus of primates

Abstract

Autoradiographic tracing procedures have been used to study the organization of retinogeniculate axons in seven primates, i.e., four species of New World monkeys, one species of Old World monkeys and two species of prosimians. These data suggest that the basic primate pattern of geniculate lamination consists of two parvocellular layers, two magnocellular layers, and two poorly developed and highly variable superficial (S) layers which are ventrally located. Ocular input to each member of each of the three pairs differs. In the macaque, the squirrel, and the saki monkey, the parvocellular layers subdivide and interdigitate into four leaflets so as to give the appearance of four parvocellular "layers." These leaflets are much less extensive in the owl and marmoset monkeys. In some individual macaque monkeys, there is further splitting of the parvocellular leaflets into subleaflets, giving the appearance of six parvocellular "layers." The prosimians (galago and slow loris) have two additional layers that are not found in pithecoid primates, and only one superficial layer is apparent. The two additional layers are termed "koniocellular" since they consist of very small cells. Finally, New and Old World monkeys have both ipsilateral and contralateral retinal input to the interlaminar zones. We conclude that the basic pattern of lateral geniculate organization is six layers, but not the traditional six. Prosimians have evolved two additional layers, the koniocellular layers, and have possibly lost one superficial layer. Both New World and Old World monkeys have elaborated the parvocellular layers by forming leaflets to varying extents. With the possible exception of the single S layer in prosimians, layers form pairs that are similar in cell types, but different in ocular input.

Geniculocortical relay of blue-off signals in the primate visual system

“…6, blue-on cells are segregated to the koniocellular layers. Five of the seven blue-off cells were located in the koniocellular layer K3 (9,24,25). The position of the remaining eight blue-off cells was not recovered histologically.…”

“…Electrode tracks were reconstructed from these sections by comparing the receptive-field positions and cell recording depths with the known anatomical eye dominance and retinotopy of the layers of the LGN (24,25).…”

The thalamic connections of motor, premotor, and prefrontal areas of cortex in a prosimian primate (Otolemur garnetti)

“…This is especially the case between prosimian primates such as galagos, with proportionately small brains and more limited behavioral repertoires, and the larger anthropoid primates, such as humans with large brains and impressive behavioral capabilities. Yet, there are certain features that characterize all primate brains, such as having visual areas V1, V2, and MT (e.g., Collins et al, 2001;Lyon and Kaas, 2002), and distinct parvocellular and magnocellular layers in the lateral geniculate nucleus of the visual thalamus (Kaas et al, 1978). Somewhat surprisingly, given the apparent differences in motor performance, galagos (and by implication, other prosimian primates) share a number of subdivisions of motor areas with anthropoid primates, including a primary motor area (M1), a supplementary motor area (SMA), a dorsal premotor area (PMD), a ventral premotor area (PMV), and a frontal eye field (FEF) (Wu et al, 2000).…”

Current Trends of fMRI in Vision Science: A Review

“…Parvo cells rarely respond well to luminance contrasts below 10%, whereas magno cells often respond to stimuli with contrasts as low as 2% (Purpura et al, 1988;Sclar et al, 1990;Shapley et al, 1981). In addition to these two, there are other types of ganglion axons that exist; the more common of these are the konio cells which are small bistratified cells (Kaas et al, 1978). They are common in the parafovea, have low contrast sensitivity, and detect color.…”