The broad aim of this project is to understand how the eye receives visual signals and sends them to the brain. Our experimental goal is to study the structure of neural connections in a poorly understood division of the visual system, called the koniocellular pathway. The cells of the koniocellular pathway make up close to 10 percent of all projections from the eye to the brain, but their functions are almost completely unknown. The fovea is a specialised region of the retina (the nerve cells w ....The broad aim of this project is to understand how the eye receives visual signals and sends them to the brain. Our experimental goal is to study the structure of neural connections in a poorly understood division of the visual system, called the koniocellular pathway. The cells of the koniocellular pathway make up close to 10 percent of all projections from the eye to the brain, but their functions are almost completely unknown. The fovea is a specialised region of the retina (the nerve cells which line the back of the eye). It is characterised by a very high density of cone photoreceptors, and is essential for high-acuity vision. This makes the fovea the most important part of the primate retina, but the high density of nerve cells there is thought to be the reason why the fovea is especially vulnerable to disease and age-related degeneration. Our aim is to analyse, using high-resolution microscopic techniques, the connections of koniocellular-pathway cells within the retina. We specifically aim to discover whether the koniocellular pathway contributes to foveal vision. Recent work from our and other laboratories has shown that many koniocellular-pathway cells receive functional connections from short-wavelength sensitive (blue) cone photoreceptors. Thus, our study will provide new insights into the connectivity of blue-cone pathways in the fovea. Although these experiments address basic scientific questions, they can lead to improved clinical practice. Understanding the wiring diagram of the retina can inform clinical studies of conditions such as glaucoma, and helps to give a rational basis for development of treatments. For example, dysfunction in blue-cone pathways is an early sign of glaucoma, so understanding the connections of blue-cone pathways in the fovea can lead to improved methods for early detection of this leading cause of blindness.Read moreRead less
Multidimensional Coding Of Visual Information In The Retina
Funder
National Health and Medical Research Council
Funding Amount
$359,431.00
Summary
Although both the retina and visual cortex are part of the central nervous system, the coding of visual information in the two laminar structures differs markedly in that all three dimensions of the cortical sheet are used to code multiple response axes but only one dimension of the retinal sheet. This project examines how visual response properties are mapped through the depth of the retina and this will provide a comparatively simple paradigm of complex information processing in the brain.
Non-standard Receptive Fields In The Primate Visual System
Funder
National Health and Medical Research Council
Funding Amount
$392,983.00
Summary
We recently discovered that an evolutionary ancient brain pathway transmits visual signals for blue-yellow colour vision. We now plan to discover whether this pathway could also contribute to form and movement perception, and to visual functions (called blindsight) that survive damage to the main visual area of the brain. This project will contribute to understanding the effects of damage to visual pathways following stroke or brain injury, as well as to understanding normal visual function.
Properties Of Human Photoreceptors Measured Using A Scanning Laser Ophthalmoscope To Illuminate And Image The Retina
Funder
National Health and Medical Research Council
Funding Amount
$352,000.00
Summary
Vision begins with the detection of light by the rod and cone photoreceptors in the retina lining the interior of the eye. Although much is already known about the way that light is detected and the signals are processed, a great deal remains to be learned. Some of the outstanding questions could be answered using modifications to a relatively new instrument called a scanning laser ophthalmoscope (SLO) which provides images of the interior of the eye. The aims of this project are to develop a mo ....Vision begins with the detection of light by the rod and cone photoreceptors in the retina lining the interior of the eye. Although much is already known about the way that light is detected and the signals are processed, a great deal remains to be learned. Some of the outstanding questions could be answered using modifications to a relatively new instrument called a scanning laser ophthalmoscope (SLO) which provides images of the interior of the eye. The aims of this project are to develop a modified SLO, which is able to measure the levels of visual pigment (rhodopsin) in the living eye, which is also able to deliver visual stimuli to the eye, and which finally is extended to use adaptive optics so that it can image and excite individual cone photoreceptors. Using this device, we will be able to measure the regeneration of visual pigment following exposures to intense illumination, to help explain the slow recovery of visual sensitivity after intense light. We will also be able to measure the electroretinogram (ERG) from localized retinal areas, to investigate how the properties of the photoreceptor cells vary across the retina. And finally we will be able not only to visualize the individual tiny cone photoreceptors, but also to stimulate them selectively, so that we can determine the responses of the different classes of cone (red-, green-, and blue-sensitive cones) in the living human eye.Read moreRead less
The retina lines the back of the eye and sends multiple movies of the visual world to the brain. This project aims to investigate how these multiple information channels are created. Descriptions of the basic pattern of wiring in the healthy retina will help clinical researchers to understand the disruptions that occur in visual disease. The precision of normal retinal wiring also delineates the precision required to restore normal function to a diseased or degenerating eye.
Metrics Of Optical Quality Predictive Of Visual Performance In Eye Disease
Funder
National Health and Medical Research Council
Funding Amount
$121,655.00
Summary
Highly precise measurement of the optical quality of the human eye (how well an image is formed by light passing through the eye) is now possible. While eye's optics can be measured, it is less clear how to report optical quality in a way that is related to how well the eye sees; optics and vision are complex. This project will attempt to find ways to describe the optical quality of the human eye that predicts how well the eye sees - both for the normal eye and eyes with disease.
Electroretinogram Recordings Of Human Scotopic Dark Adaptation Following Intense Bleaching Exposures
Funder
National Health and Medical Research Council
Funding Amount
$272,250.00
Summary
After a human subject has been exposed to intense illumination, it can take many minutes for the eye to regain full sensitivity, as one experiences (for example) when entering a dark cave after being out on a bright sunny beach. This project will investigate the processes that occur in the cells of retina lining the back of the eye, that prevent the instantaneous recovery of vision following intense illumination. Electrical recordings will be made from the eyes of normal individuals, using new t ....After a human subject has been exposed to intense illumination, it can take many minutes for the eye to regain full sensitivity, as one experiences (for example) when entering a dark cave after being out on a bright sunny beach. This project will investigate the processes that occur in the cells of retina lining the back of the eye, that prevent the instantaneous recovery of vision following intense illumination. Electrical recordings will be made from the eyes of normal individuals, using new techniques that allow the activity of different types of nerve cell in the retina to be monitored. The study will determine how it is that events in the light-detector cells of the eye (the rod and cone photoreceptors) influence the activity of subsequent nerve cells in the visual system, and how these events contribute to the poor vision that one experiences following bright lights.Read moreRead less
Using Contextual Effects To Test Theories Of Coding In Visual Cortex
Funder
National Health and Medical Research Council
Funding Amount
$200,500.00
Summary
The visual cortex is the main structure in the brain that processes the visual scene. Cells in the cortex respond selectively to features of the scene such as the orientation of objects, the direction they move and their brightness relative to the background. Cortical cells are arranged in a topographic map of visual space, so that nearby cells respond to light from nearby parts of the image. Recent advances have shown that cells talk to each other so a stimulus in one part of the visual field c ....The visual cortex is the main structure in the brain that processes the visual scene. Cells in the cortex respond selectively to features of the scene such as the orientation of objects, the direction they move and their brightness relative to the background. Cortical cells are arranged in a topographic map of visual space, so that nearby cells respond to light from nearby parts of the image. Recent advances have shown that cells talk to each other so a stimulus in one part of the visual field can influence the responses of cells looking at other regions. This communication between cells is important in guiding the brain to focus on areas of the visual scene that are most important, a process known as attention. An example would be that a mouse moving through the periphery of someone's vision would attract their attention away from objects elsewhere in the scene. This project is designed to study the way that cells in the visual cortex cooperate to guide attention. Attention is important because it reduces the need to process all the detail in the visual scene with the same level of accuracy, leaving more resources free to process what is important. Attention deficits are a problem for people with dyslexia, so understanding the physiological basis of attention is an important goal. As well as attention, the visual system has a range of other mechanisms to select important information from the visual scene. For example, visual adaptation tends to improve the ability to code changes in the visual scene at the expense of reducing the sensitivity of the system overall. This project will investigate the relationship between attentional and adaptive mechanisms in the visual cortex. We expect to establish the precise physiological mechanisms that drive adaptive and attentional mechanisms in the mammalian brain.Read moreRead less
Distribution Of Neurotransmitter Receptors On Identified Cell Populations In The Primate Retina
Funder
National Health and Medical Research Council
Funding Amount
$421,812.00
Summary
Neurons (nerve cells) communicate with each other by releasing chemicals called neurotransmitters at specialized sites called synapses. Each neuron has synaptic receptors, which determine how it will respond to neurotransmitters released by other neurons. The molecular structure and function of these receptors is well understood. Much less is known about the rules that govern which receptor types are expressed by each type of neuron, and how these receptors are distributed to the appropriate syn ....Neurons (nerve cells) communicate with each other by releasing chemicals called neurotransmitters at specialized sites called synapses. Each neuron has synaptic receptors, which determine how it will respond to neurotransmitters released by other neurons. The molecular structure and function of these receptors is well understood. Much less is known about the rules that govern which receptor types are expressed by each type of neuron, and how these receptors are distributed to the appropriate synapses so as to allow the normal function of the nervous system. We will study the distribution of neurotransmitter receptors on identified neurons in the retina. The retina is part of the central nervous system and its highly ordered structure makes it an ideal model nervous system. We will compare the distribution of receptors on neurons that play distinct functional roles in colour and movement detection. These experiments will advance our understanding of the normal functioning of the nervous system.Read moreRead less
Synaptic Connectivity Of Colour Pathways In Primate Retina
Funder
National Health and Medical Research Council
Funding Amount
$367,500.00
Summary
The first step in the visual process occurs when light enters the eye and activates specialised nerve cells called photoreceptors. The photoreceptors for daytime vision (called cones for their cone-like shape) comprise three types, which are sensitive to the long- (red), medium- (green) or short-wavelength (blue) regions of the visible spectrum. Although the properties of the cones are well known, the way in which they are functionally connected to nerve pathways for vision is not clearly unders ....The first step in the visual process occurs when light enters the eye and activates specialised nerve cells called photoreceptors. The photoreceptors for daytime vision (called cones for their cone-like shape) comprise three types, which are sensitive to the long- (red), medium- (green) or short-wavelength (blue) regions of the visible spectrum. Although the properties of the cones are well known, the way in which they are functionally connected to nerve pathways for vision is not clearly understood. Clinical research has shown that reduced sensitivity to blue light is a feature of the early stages of certain visual diseases (for example, glaucoma), so it is important to know how the short-wavelength (blue) cones contribute to visual functions such as form, motion and colour perception. Such knowledge can help to design better tests for diagnosis of visual disorders, and will improve our understanding of the normal function of the visual system in the human brain. In this project the connections of neurones in the primate retina (the nerve cells which line the back of the eye) will be analysed. The blue cones and other nerve cells will be identified using contemporary anatomical methods (double- and triple-label immunocytochemistry) combined with a new method for high-resolution light microscopy, called deconvolution microscopy. Immunocytochemistry is a method borrowed from the field of immunology, where specific antibodies are raised which bind selectively to label specific populations of neurones. Deconvolution microscopy allows rapid and simultaneous visualisation of multiple labelled cell classes, at a resolution close to the limit of the light microscope. Together, these techniques allow the wiring diagram of the blue cones within the retina to be analysed to a higher level of accuracy than previously achieved. The results will improve our understanding of the role of blue-cone circuits in normal vision and visual disorders.Read moreRead less