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Farran Briggs, Martin W. Usrey; How colorful is corticogeniculate feedback?. Journal of Vision 2007;7(15):10. doi: 10.1167/7.15.10.
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© ARVO (1962-2015); The Authors (2016-present)
The function of the primate corticogeniculate pathway in early visual processing has remained elusive. Although corticogeniculate neurons are anatomically diverse - a diversity that reflects the segregated organization of inputs and outputs with the magnocellular and parvocellular layers of the LGN - their local circuitry suggests possible mixing from the magnocellular and parvocellular streams. In order to understand the function of this important feedback pathway, including the magnocellular and parvocellular contributions, an examination of the functional response properties of individual corticogeniculate neurons is required. We employed electrical stimulation in the LGN to identify corticogeniculate neurons via antidromic activation in the alert macaque monkey. We then measured the axon conduction latencies of neurons and characterized their visual response properties using luminance-modulated and cone-isolating gratings that varied in contrast, temporal frequency and spatial frequency. Neurons were studied while the animal performed a simple fixation task. Our results show that corticogeniculate neurons in the monkey are functionally diverse. In general, corticogeniculate neurons with short conduction latencies are complex cells that respond well to low contrast and high temporal frequency stimuli. Corticogeniculate neurons with longer conduction latencies are simple cells that respond less well to low contrast and high temporal frequency stimuli. Corticogeniculate neurons also differ in the cone contributions to their responses. These results support the view that the corticogeniculate pathway in the primate consists of multiple, functionally diverse cell types carrying distinct information to the LGN.
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