title: An experimentally induced duplication of retinotopic mapping within the hamster primary visual cortex.
abstract: Primary cortical areas normally have a single mapping of the receptor array arising from a 'point-to-point' projection from the thalamus. We show that, for the visual cortex, this simple mapping rule breaks down when retinal input to the thalamus is altered. We utilize the monocular enucleation paradigm, which alters subcortical mappings ipsilateral to the remaining eye. We show that this manipulation produces an altered visuotopic map in area 17 with two separated, mirror-imaged representations of the central visual field. Furthermore, thalamic point-to-point connectivity is dramatically changed. There are now two overlapping geniculocortical projections: the predominant projection maps with apparently normal topography, and a second projection maps with the opposite polarity. The plane of symmetry of the duplicated anatomical projection coincides precisely with the functional map reversal and, notably, geniculocortical magnification factors are identical in the two projections. We suggest that the duplicated, abnormal geniculocortical projection is retinotopically matched to the normal projection. We speculate that aberrant geniculocortical terminals are stabilized because they have coherent activity patterns with topographically normal terminals.
authors.affiliation: Department of Physiology, Anatomy and Genetics, Oxford, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Trevelyan
authors.forename: A L
authors.initials: AL
authors.lastname: Upton
authors.forename: Patricia M
authors.initials: PM
authors.lastname: Cordery
authors.forename: Ian D
authors.initials: ID
authors.lastname: Thompson
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001931:Brain Mapping; D006224:Cricetinae; D015353:Eye Enucleation / Q000379:methods; D007839:Functional Laterality / Q000502:physiology; D005829:Geniculate Bodies / Q000033:anatomy & histology / Q000378:metabolism; D008954:Models, Biological; D009186:Myelin Sheath / Q000378:metabolism; D009474:Neurons / Q000502:physiology; D010775:Photic Stimulation; D012160:Retina / Q000033:anatomy & histology / Q000502:physiology; D014793:Visual Cortex / Q000033:anatomy & histology* / Q000254:growth & development*; D014794:Visual Fields / Q000502:physiology*; D014795:Visual Pathways / Q000033:anatomy & histology* / Q000502:physiology