Abstract
The lateral geniculate nucleus (LGN) is the primary thalamic nucleus that relays visual information from the retina to the primary visual cortex (V1) and has been extensively studied in non-human primates. A key feature of the LGN is the segregation of retinal inputs into different cellular layers characterized by their differential responses to red-green (RG) color (L/M opponent), blue-yellow (BY) color (S-cone opponent) and achromatic (Ach) contrast. In this study we use high-field functional magnetic resonance imaging (4 tesla, 3.6 × 3.6 × 3 mm3) to record simultaneously the responses of the human LGN and V1 to chromatic and Ach contrast to investigate the LGN responses to color, and how these are modified as information transfers between LGN and cortex. We find that the LGN has a robust response to RG color contrast, equal to or greater than the Ach response, but a significantly poorer sensitivity to BY contrast. In V1 at low temporal rates (2 Hz), however, the sensitivity of the BY color pathway is selectively enhanced, rising in relation to the RG and Ach responses. We find that this effect generalizes across different stimulus contrasts and spatial stimuli (1-d and 2-d patterns), but is selective for temporal frequency, as it is not found for stimuli at 8 Hz. While the mechanism of this cortical enhancement of BY color vision and its dynamic component is unknown, its role may be to compensate for a weak BY signal originating from the sparse distribution of neurons in the retina and LGN.
Highlights
The lateral geniculate nucleus (LGN) is the primary thalamic nucleus for the neural pathway linking the retina to the primary visual cortex (V1)
V1 shows a robust response to BY stimuli; for the ring stimuli the cortical response to the BY stimulus is similar to that for the RG and Ach stimuli, whereas in the LGN the BY response was significantly less than the RG response
A key feature of the comparison of the responses between the LGN and V1 is a marked increase in the BY response relative to the Rt and Ach, which occurs for both ring and check stimuli
Summary
The lateral geniculate nucleus (LGN) is the primary thalamic nucleus for the neural pathway linking the retina to the primary visual cortex (V1). One key feature of the LGN is the segregation of retinal inputs into different layers: the retinal parvocellular (P)-cells project to dorsal layers 3–6, whereas the magnocellular (M)-cell population projects to ventral layers 1 and 2, with further cell types forming the koniocellular layers of the intra-laminar regions. The neurons in these different layers have distinct neurophysiological and anatomical properties, and provide the basis for a functional segregation based on chromatic and spatio-temporal properties. S-cone opponency, the basis of blueyellow (BY) color vision, is carried from retina to cortex by sparse, specialized neurons mainly found in the koniocellular layers of the LGN (Martin et al, 1997; Chatterjee & Callaway, 2003; Dacey & Packer, 2003)
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