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Stephen D Hooser, Jan-Alexander F Heimel, Sooyoung Chung, Sacha B Nelson; Receptive field properties and laminar organization in the lateral geniculate nucleus of the gray squirrel (sciurus carolinensis). Journal of Vision 2003;3(9):369. doi: 10.1167/3.9.369.
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© ARVO (1962-2015); The Authors (2016-present)
Squirrels are diurnal rodents with large eyes, dichromatic color vision, large striate and extrastriate visual cortical areas, and good visual acuity. They are abundant, inexpensive, and offer many technical advantages in common with the poorly-sighted rat and mouse. We have characterized receptive field properties of single neurons in the lateral geniculate nucleus of the anesthetized gray squirrel using white noise, monochromatic and cone-isolating colored spots and annuli, and sinusoidal gratings. In the squirrel, the LGN contains five layers of cells with alternating retinal innervation, labeled (medial to lateral) 1, 2, 3a, 3b, and 3c, with 3c bordering the optic tract. The contralateral input is to layers 1, 3a, and 3c, while layers 2 and 3b receive ipsilateral input. Cells in layers 1 and 2 show very sustained responses to constant stimulation, and neurons in layers 3a, 3b, and 3c show more transient responses. Most neurons in layers 1–2 have response latencies between 20-30ms, and some cells in these layers show color antagonism between the center and surround. Cells in layers 3a and 3b are quite heterogeneous. About half of the cells in 3a and 3b show strong center-surround organization and have latencies around 20–30ms, while the other cells show less activity, long, widely distributed response latencies, and do not tend to show strong center-surround organization. While many properties of these short latency cells in 3a and 3b overlap those of cells in layers 1–2, the 3a–3b cells are more transient and show less linearity of spatial summation than cells in layers 1–2, which are quite linear. We discuss how these cell types and their laminar distributions compare to those observed in dichromatic primates and carnivores.
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