The development of human visual cortex and clinical implications

Abstract

The primary visual cortex (V1) is the first cortical area that processes visual information. Normal development of V1 depends on binocular vision during the critical period, and age-related losses of vision are linked with neurobiological changes in V1. Animal studies have provided important details about the neurobiological mechanisms in V1 that support normal vision or are changed by visual diseases. There is very little information, however, about those neurobiological mechanisms in human V1. That lack of information has hampered the translation of biologically inspired treatments from preclinical models to effective clinical treatments. We have studied human V1 to characterize the expression of neurobiological mechanisms that regulate visual perception and neuroplasticity. We have identified five stages of development for human V1 that start in infancy and continue across the life span. Here, we describe these stages, compare them with visual and anatomical milestones, and discuss implications for translating treatments for visual disorders that depend on neuroplasticity of V1 function.

Keywords: GABAergic; amblyopia; development; glutamatergic; human visual cortex; receptors; synaptic plasticity.

Figure 1

Summary chart for development of human visual milestones. Notes: A summary of the development of key visual perceptual milestones across the life span. The top panel shows the stages of human development (infants, young children, older children, teens, young adults, older adults), and associated ages in months and years (as presented by Siu et al22). The rows below illustrate the approximate timing of onset and emergence (green arrows), adult-like levels (gray shade with black arrows), and loss of function (red arrows). References linked to each milestone are provided in the right column. Abbreviations: V1, primary visual cortex; mo, months.

Figure 2

Summary chart for development of human V1 anatomical milestones. Notes: A summary of the development of key neuroanatomical milestones in human V1 across the life span. The top panel shows the stages of human development (prenatal, infants, young children, older children, teens, young adults, older adults), and associated ages in months and years (as presented by Siu et al22). The rows below illustrate the approximate timing of onset and emergence (green arrows), adult-like levels and structure (gray shade with black arrows), and loss of expression (red arrows). Black dots refer to anatomical milestones that are completed before birth. References linked to each milestone are provided in the right column. Abbreviations: V1, primary visual cortex; mo, months.

Figure 3

Summary chart for development of human V1 neurobiological milestones. Notes: A summary of the development of key neurobiological milestones in human V1 across the life span. The top panel shows the stages of human development (infants, young children, older children, teens, young adults, older adults), and associated ages in months and years (as presented by Siu et al22). The rows below illustrate the approximate timing of onset and emergence (green arrows), peak expression (gray shades), adult-like levels (gray shade with black arrows), and loss of expression (red arrows). References linked to each milestone are provided in the right column. Abbreviations: V1, primary visual cortex; mo, months; MBP, myelin basic protein.

Figure 4

Summary chart of glutamatergic and GABAergic receptor subunits. Notes: This figure presents a summary of some key glutamate (AMPAR and NMDAR) and GABA (GABA_A) receptor subunit compositions that regulate neuroplasticity in the primary visual cortex. The columns represent functional significance of the balance of NMDA:AMPA (top), GluN2A:GluN2B (middle), and GABA_Aα1:GABA_Aα3 (bottom). More juvenile synapses are dominated by more NMDAR, GluN2B containing NMDAR, and GABA_Aα3 containing GABA_A receptors that allow for LTP in excitatory synapses and slower kinetics through the receptors. More mature synapses are dominated by more AMPAR, GluN2A containing NMDAR, and GABA_Aα1 containing GABA_A receptors that allow for more LTD in excitatory synapses, and faster kinetics through the receptors. Abbreviations: GABA, gamma-aminobutyric acid; LTD, long-term depression; AMPAR, AMPA receptor; NMDAR, N-methyl-d-aspartate receptor; LTP, long-term potentiation.