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Retinotopy
Retinotopy (from Greek τόπος (tópos) 'place') is the mapping of visual input from the retina to neurons, particularly those neurons within the visual stream. For clarity, 'retinotopy' can be replaced with 'retinal mapping', and 'retinotopic' with 'retinally mapped'.
Visual field maps (retinotopic maps) are found in many amphibian and mammalian species, though the specific size, number, and spatial arrangement of these maps can differ considerably. Sensory topographies can be found throughout the brain and are critical to the understanding of one's external environment. Moreover, the study of sensory topographies and retinotopy in particular has furthered our understanding of how neurons encode and organize sensory signals.
Retinal mapping of the visual field is maintained through various points of the visual pathway including but not limited to the retina, the dorsal lateral geniculate nucleus, the optic tectum, the primary visual cortex (V1), and higher visual areas (V2-V4).
Retinotopic maps in cortical areas other than V1 are typically more complex, in the sense that adjacent points of the visual field are not always represented in adjacent regions of the same area. For example, in the second visual area (V2), the map is divided along an imaginary horizontal line across the visual field, in such a way that the parts of the retina that respond to the upper half of the visual field are represented in cortical tissue that is separated from those parts that respond to the lower half of the visual field. Even more complex maps exist in the third and fourth visual areas V3 and V4, and in the dorsomedial area (V6). In general, these complex maps are referred to as second-order representations of the visual field, as opposed to first-order (continuous) representations such as V1.
Additional retinotopic regions include ventral occipital (VO-1, VO-2), lateral occipital (LO-1, LO-2), dorsal occipital (V3A, V3B), and posterior parietal cortex (IPS0, IPS1, IPS2, IPS3, IPS4).
In the late 19th-century, independent animal studies including some on dogs by the physiologist Hermann Munk and some on monkeys by the neurologist David Ferrier elucidated that lesions to the occipital and parietal lobes induced blindness. Around the turn of the century, Swedish neurologist and pathologist Salomon Henschen had a prolific body of work on the mind that included much research on neuropathology. Although only partially accurate, he correlated the location of brain lesion to areas of occluded vision. He became an early proponent of the existence of a visual map which he called the "cortical retina".
Early accurate mapping of the visual map arose from studying cranial injuries in war. Maps were described and analyzed by the Japanese ophthalmologist Tatsuji Inouye when studying soldiers' injuries incurred in the Russo-Japanese War, although his work on the subject—published in 1909 through a German monograph—was largely ignored and abandoned to obscurity. Independently of Inouye a few years later, the British neurologist Gordon Holmes made similar advances studying the injuries suffered by soldiers in World War I. Both scientists observed correlations between the position of an entry wound and the presented visual field loss in the patient. (See Fishman, 1997 for an in-depth historical review.)
The "chemoaffinity hypothesis" was established by Sperry et al in 1963 in which it is thought that molecular gradients in both presynaptic and postsynaptic partners within the optic tectum organize developing axons into a coarse retinotopic map. This was established after a series of seminal experiments in fish and amphibians showed that retinal ganglion axons were already retinotopically organized within the optic tract and if severed, would regenerate and project back to retinotopically appropriate locations. Later, it was identified that receptor tyrosine kinases family EphA and a related EphA binding molecule referred to as ephrin-A family are expressed in complementary gradients in both the retina and the tectum. More specifically in the mouse, Ephrin A5 is expressed along the rostral-caudal axis of the optic tectum whereas the EphB family is expressed along the medio-lateral axis. This bimodal expression suggests a mechanism for the graded mapping of the temporal-nasal axis and the dorsoventral axis of the retina.
Hub AI
Retinotopy AI simulator
(@Retinotopy_simulator)
Retinotopy
Retinotopy (from Greek τόπος (tópos) 'place') is the mapping of visual input from the retina to neurons, particularly those neurons within the visual stream. For clarity, 'retinotopy' can be replaced with 'retinal mapping', and 'retinotopic' with 'retinally mapped'.
Visual field maps (retinotopic maps) are found in many amphibian and mammalian species, though the specific size, number, and spatial arrangement of these maps can differ considerably. Sensory topographies can be found throughout the brain and are critical to the understanding of one's external environment. Moreover, the study of sensory topographies and retinotopy in particular has furthered our understanding of how neurons encode and organize sensory signals.
Retinal mapping of the visual field is maintained through various points of the visual pathway including but not limited to the retina, the dorsal lateral geniculate nucleus, the optic tectum, the primary visual cortex (V1), and higher visual areas (V2-V4).
Retinotopic maps in cortical areas other than V1 are typically more complex, in the sense that adjacent points of the visual field are not always represented in adjacent regions of the same area. For example, in the second visual area (V2), the map is divided along an imaginary horizontal line across the visual field, in such a way that the parts of the retina that respond to the upper half of the visual field are represented in cortical tissue that is separated from those parts that respond to the lower half of the visual field. Even more complex maps exist in the third and fourth visual areas V3 and V4, and in the dorsomedial area (V6). In general, these complex maps are referred to as second-order representations of the visual field, as opposed to first-order (continuous) representations such as V1.
Additional retinotopic regions include ventral occipital (VO-1, VO-2), lateral occipital (LO-1, LO-2), dorsal occipital (V3A, V3B), and posterior parietal cortex (IPS0, IPS1, IPS2, IPS3, IPS4).
In the late 19th-century, independent animal studies including some on dogs by the physiologist Hermann Munk and some on monkeys by the neurologist David Ferrier elucidated that lesions to the occipital and parietal lobes induced blindness. Around the turn of the century, Swedish neurologist and pathologist Salomon Henschen had a prolific body of work on the mind that included much research on neuropathology. Although only partially accurate, he correlated the location of brain lesion to areas of occluded vision. He became an early proponent of the existence of a visual map which he called the "cortical retina".
Early accurate mapping of the visual map arose from studying cranial injuries in war. Maps were described and analyzed by the Japanese ophthalmologist Tatsuji Inouye when studying soldiers' injuries incurred in the Russo-Japanese War, although his work on the subject—published in 1909 through a German monograph—was largely ignored and abandoned to obscurity. Independently of Inouye a few years later, the British neurologist Gordon Holmes made similar advances studying the injuries suffered by soldiers in World War I. Both scientists observed correlations between the position of an entry wound and the presented visual field loss in the patient. (See Fishman, 1997 for an in-depth historical review.)
The "chemoaffinity hypothesis" was established by Sperry et al in 1963 in which it is thought that molecular gradients in both presynaptic and postsynaptic partners within the optic tectum organize developing axons into a coarse retinotopic map. This was established after a series of seminal experiments in fish and amphibians showed that retinal ganglion axons were already retinotopically organized within the optic tract and if severed, would regenerate and project back to retinotopically appropriate locations. Later, it was identified that receptor tyrosine kinases family EphA and a related EphA binding molecule referred to as ephrin-A family are expressed in complementary gradients in both the retina and the tectum. More specifically in the mouse, Ephrin A5 is expressed along the rostral-caudal axis of the optic tectum whereas the EphB family is expressed along the medio-lateral axis. This bimodal expression suggests a mechanism for the graded mapping of the temporal-nasal axis and the dorsoventral axis of the retina.