Development of forward and feedback connections between areas V1 and V2 of human visual cortex. 1993

A Burkhalter
Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110.

We have determined the sequence in which forward connections between visual cortical areas V1 and V2, and feedback connections between V2 and V1 develop in humans. For this purpose Dil was injected into V1 and V2 of postmortem brains of different pre- and postnatal ages. The laminar distribution of labeled fibers and cell bodies in V1 and V2 indicates that forward and feedback connections emerge shortly before birth. The development of both pathways proceeds over several postnatal months such that the laminar termination pattern of forward connections appears relatively mature before feedback connections reach their mature form. At 37 weeks of gestation both forward and feedback connections originate exclusively from deep-layer neurons, which extend axons in deep layers only. By 9 d postnatal, forward connections from V1 to V2, in addition to layers 5 and 6, also arise from neurons in layer 4B of V1. At this stage for the first time forward fibers enter layer 4 at the topographically appropriate location of V2. At 9 d postnatal most feedback fibers from V2 still occupy deep layers of V1 but many, through interstitial growth, elaborate vertical sprouts at regular intervals along the length of horizontal axons. As feedback connections mature, distal segments of horizontal axons are pruned back to branch points and fibers assume L-shaped configurations. By 7 weeks of age forward fibers from V1 enter V2 through deep and superficial layers and provide input to layers 3 and 4. At this stage feedback fibers from V2 have entered layer 4B of V1. By 4 months of age forward connections have assumed all the laminar characteristics of mature connections; that is, they arise from layers 2/3, 4B, 5, and 6 of V1, and terminate in layers 3 and 4 of V2. In sharp contrast, at 4 months of age feedback connections to V1 are still immature, showing terminations in layers 4B, 5, and 6 but no input to layer 2/3. The protracted postnatal emergence of feedback connections is similar to that of local long-range connections within layer 2/3 of V1 (Burkhalter et al., 1993). Since both of these circuits are thought to provide information about the context in which objects are seen, it is interesting to speculate that the late onset of texture segmentation in infants (Atkinson and Braddick, 1992; Sireteanu and Rieth, 1992) may be related to the postnatal maturation of specific intracortical circuits.

UI MeSH Term Description Entries
D007223 Infant A child between 1 and 23 months of age. Infants
D007231 Infant, Newborn An infant during the first 28 days after birth. Neonate,Newborns,Infants, Newborn,Neonates,Newborn,Newborn Infant,Newborn Infants
D008856 Microscopy, Fluorescence Microscopy of specimens stained with fluorescent dye (usually fluorescein isothiocyanate) or of naturally fluorescent materials, which emit light when exposed to ultraviolet or blue light. Immunofluorescence microscopy utilizes antibodies that are labeled with fluorescent dye. Fluorescence Microscopy,Immunofluorescence Microscopy,Microscopy, Immunofluorescence,Fluorescence Microscopies,Immunofluorescence Microscopies,Microscopies, Fluorescence,Microscopies, Immunofluorescence
D011247 Pregnancy The status during which female mammals carry their developing young (EMBRYOS or FETUSES) in utero before birth, beginning from FERTILIZATION to BIRTH. Gestation,Pregnancies
D002232 Carbocyanines Compounds that contain three methine groups. They are frequently used as cationic dyes used for differential staining of biological materials. Carbocyanine
D005246 Feedback A mechanism of communication within a system in that the input signal generates an output response which returns to influence the continued activity or productivity of that system. Feedbacks
D005260 Female Females
D005865 Gestational Age The age of the conceptus, beginning from the time of FERTILIZATION. In clinical obstetrics, the gestational age is often estimated from the onset of the last MENSTRUATION which is about 2 weeks before OVULATION and fertilization. It is also estimated to begin from fertilization, estrus, coitus, or artificial insemination. Embryologic Age,Fetal Maturity, Chronologic,Chronologic Fetal Maturity,Fetal Age,Maturity, Chronologic Fetal,Age, Embryologic,Age, Fetal,Age, Gestational,Ages, Embryologic,Ages, Fetal,Ages, Gestational,Embryologic Ages,Fetal Ages,Gestational Ages
D006651 Histocytochemistry Study of intracellular distribution of chemicals, reaction sites, enzymes, etc., by means of staining reactions, radioactive isotope uptake, selective metal distribution in electron microscopy, or other methods. Cytochemistry
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man

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