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Bypassing VI: a direct geniculate input to area MT. Nat Neurosci 7:1123-1128

Beckman Vision Center, University of California, 10 Koret Way, San Francisco, California 94143, USA. <>
Nature Neuroscience (Impact Factor: 14.98). 11/2004; 7(10):1123-8. DOI: 10.1038/nn1318
Source: PubMed

ABSTRACT Thalamic nuclei are thought to funnel sensory information to the brain's primary cortical areas, which in turn transmit signals afresh to higher cortical areas. Here we describe a direct projection in the macaque monkey from the lateral geniculate nucleus (LGN) to the motion-selective middle temporal area (MTor V5), a cortical area not previously considered 'primary'. The constituent neurons are mostly koniocellular, send virtually no collateral axons to primary visual cortex (V1) and equal about 10% of the V1 population innervating MT. This pathway could explain the persistence of motion sensitivity in subjects following injury to V1, suggesting more generally that residual perception after damage in a primary area may arise from sparse thalamic input to 'secondary' cortical areas.

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    • "However, it is not clear whether these effects are due to plastic cellular changes in neurons in the LGN (Eysel and Wolfhard, 1984) and visual cortex (Gilbert and Wiesel, 1992) described by neurophysiologists, and/or due to changes in extrageniculate-cortical pathways that include the SC, pulvinar, and interhemispheric pathways (Bridge et al., 2008; Bourne, 2010). In addition, the newly discovered direct connection from LGN and medial temporal (MT) cortex without relay at primary visual cortex may be relevant to compensatory changes (Sincich et al., 2004; Nassi et al., 2006). "
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    • "It is possible, and even likely, that preferences for higher speeds are mediated at least in part by a parallel input to V5 that by-passes V1, as well as by parallel cortical inputs to V5 from V2 and V3 (Ponce et al., 2011). It has long been known that prestriate visual areas, among them area V5, receive direct inputs from both the LGN and the inferior pulvinar (Cragg, 1969; Benevento and Rezak, 1976; Fries, 1981; Yukie and Iwai, 1981; ffytche et al., 1995a; Sincich et al., 2004; Leh et al., 2008; Shigihara and Zeki, 2013, 2014a). What has not been explored yet is how the ''V1-bypassing'' subcortical inputs to V5 co-operate with the parallel cortical input to it from V1 in sculpting the properties and receptive field structures of cells in V5 and other visual areas, especially since there may be a correspondence between directional preferences and speed tuning (Perrone and Krauzlis, 2008). "
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    ABSTRACT: Area V5 of the visual brain, first identified anatomically in 1969 as a separate visual area, is critical for the perception of visual motion. As one of the most intensively studied parts of the visual brain, it has yielded many insights into how the visual brain operates. Among these are: the diversity of signals that determine the functional capacities of a visual area; the relationship between single cell activity in a specialized visual area and perception of, and preference for, attributes of a visual stimulus; the multiple asynchronous inputs into, and outputs from, an area as well as the multiple operations that it undertakes asynchronously; the relationship between activity at given, specialized, areas of the visual brain and conscious awareness; and the mechanisms used to " bind " signals from one area with those from another, with a different specialization, to give us our unitary perception of the visual world. Hence V5 is, in a sense, a microcosm of the visual world and its study gives important insights into how the whole visual brain is organized—anatomically, functionally and perceptually.
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    • "Animal studies have shown that this region not only receives projections that are routed over the primary visual cortex but also subcortical ones. The existence of a direct projection from LGN to MT in the brain of macaque monkeys was shown using a retrograde tracing technique (Sincich, et al., 2004; Yukie and Iwai, 1981). A direct connection between MT and pulvinar, which receives input of the superior colliculus has been anatomically described by Standage and Benevento (Standage and Benevento, 1983). "
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