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.
Saccadic Eye Movements And The Neural Basis Of Visual Perception
Funder
National Health and Medical Research Council
Funding Amount
$570,828.00
Summary
The eye has a restricted central area that has good vision. We must make very frequent eye movements to build up a high resolution picture of a particular image. The term active vision is used to describe the requirement of coordinating the eye movements with the visual system. The study of active vision at the neural level requires experiments that combine single cell recording with behaviour. This study will explore which parts of the brain are involved in active vision in monkeys.
Role Of Cortico-cortical Connections In Mediating Cerebral Cortex Plasticity: Visual Cortex Model
Funder
National Health and Medical Research Council
Funding Amount
$362,500.00
Summary
In mammals injury to the retina not only affects the neurones within the eye but also induces changes in the other parts of the brain, particularly in the visual cortex. It has been found that after retinal injury cells in the visual cortex, normally receiving an input from the injured part of the retina, now receive an input from adjacent normal retina ( ectopic receptive field ). All mammals with well developed vision have a large number of separate visual cortical areas (more than 30 in prima ....In mammals injury to the retina not only affects the neurones within the eye but also induces changes in the other parts of the brain, particularly in the visual cortex. It has been found that after retinal injury cells in the visual cortex, normally receiving an input from the injured part of the retina, now receive an input from adjacent normal retina ( ectopic receptive field ). All mammals with well developed vision have a large number of separate visual cortical areas (more than 30 in primates). These areas are arranged in a hierarchy in which it is thought that as features of the visual stimuli become more complex they are discriminated in the areas higher in the hierarchy. These higher-order areas also project back to lower-order areas. This feedback activity from the higher areas can be reversibly abolished by cooling a given area to about 10oC and then rewarming it back to its normal temperature. We will try to determine if in cats (animals with well developed vision) following damage to a small region of the retina the feedback activity from higher visual cortical areas affects the ectopic receptive fields in the lower visual cortical areas. Another possibility is that the ectopic receptive field apparent following retinal damage might depend on horizontal connections within the particular cortical area, running from normal cortex to the area of cortex affected by the lesion. We propose to test this idea by blocking reversibly (with chemical agents) transmission of these horizontal fibres and determining the characteristics of neurones in the area affected by the lesion. Understanding the role of feedback and horizontal cortico-cortical connections in establishing new ectopic receptive fields following spatially delineated damage to the retina will help us to understand the mechanisms underlying perceptual distortions and visual hallucinations which occur following retinal traumas or some age-related retinal degenerations.Read moreRead less
Integration Of Information By Cells In Mammalian Visual Cortices: Role Of Feedforward And Feedback Inputs.
Funder
National Health and Medical Research Council
Funding Amount
$294,098.00
Summary
In highly 'visual' mammals, such as humans or domestic cats information channels originating in the retina extract and process in parallel information about certain features of the visual world such as shape or motion. The extracted information is sent to the primary visual cortex in the brain. The primary visual cortex 'distributes' this information to different 'higher-order' cortical areas which process the information further. Nerve cells in visual cortices have clearly defined receptive fie ....In highly 'visual' mammals, such as humans or domestic cats information channels originating in the retina extract and process in parallel information about certain features of the visual world such as shape or motion. The extracted information is sent to the primary visual cortex in the brain. The primary visual cortex 'distributes' this information to different 'higher-order' cortical areas which process the information further. Nerve cells in visual cortices have clearly defined receptive fields (RFs), that is, regions of the visual space from which appropriate visual stimuli will activate the cell. Contrary to the previous assumptions however, many of the basic RF properties of cortical neurones are not static but appear to depend on constant dynamic interplay between different components of nerve network in which the neurones are embedded. We wish to study the dynamic changes in the spatial structure of RFs of single neurones in mammalian primary visual cortex. We will examine changes in the structure of RFs of shape processing neurones when low contrast, large visual stimuli are presented. Since the low contrast stimuli extending beyond the confines of RFs of cortical neurones are akin to those in the natural visual scenes we hope to gain insights concerning mechanisms underlying perceptual processing of shapes in natural scenes. We will also study the spatial organization of RFs of neurones in primary visual cortex during reversible inactivation of higher-order visual areas. This will allow us to gain insights concerning the role of 'feedback' projections from the higher-order areas. Furthermore, we will study the responses of cells in one of the higher-order motion processing cortical areas. Comparing the responses in this area to complex motions during normal conditions with those during reversible inactivation of one of the reciprocally connected areas will provide us with insights concerning the mechanisms underlying processing of complex motions.Read moreRead less
Neuronal Basis Of Stimulus Dependent Receptive Field Properties And The Role Of Feedback Projections
Funder
National Health and Medical Research Council
Funding Amount
$258,000.00
Summary
In mammals with a number of distinct visual cortical areas the processing of information in the visual cortex largely follows a hierarchical order. It has been widely assumed that the neurones at the highest processing level in the visual system are capable of extracting behaviorally significant features from the external visual world by virtue of their large receptive fields. However, there are massive and dense inter-connections between the cortical areas and intra-connections between the neur ....In mammals with a number of distinct visual cortical areas the processing of information in the visual cortex largely follows a hierarchical order. It has been widely assumed that the neurones at the highest processing level in the visual system are capable of extracting behaviorally significant features from the external visual world by virtue of their large receptive fields. However, there are massive and dense inter-connections between the cortical areas and intra-connections between the neurones within the same cortical area. For example the information at the higher processing levels may flow back to the lower ones via the feedback connections. Thus, it is conceivable that the neurones in the primary visual cortex (at the first stage of cortical processing) may posses the properties allowing them to integrate a considerable amount of information from a large area in visual space due to the existence of a dense web of connections. We wish to study the neuronal basis of perceptually related properties in primary visual cortex by examining the detailed receptive field properties of individual neurons and their response characteristics when more complicated visual stimuli are presented in visual space. We will also examine the influence of the feedback connections on the properties of these neurones by silencing the higher-order visual cortical areas which inversely connect to primary visual cortex. It is hoped that by relating our understanding of the basic neuronal properties to their functional roles in visual processing we will obtain further insights concerning the contributions of individual visual cortical areas (primary visual cortex in this project) to the function of visual perception.Read moreRead less
Combining input from vision and hearing greatly enhances perception when information from one of these senses is degraded or incomplete, such as when tracking objects in foggy, dark or noisy places. This enhancement is of considerable importance because degraded input is the daily situation faced by many people with hearing or vision impairment. We will study the neural processes underlying our ability to combine vision and hearing to create a more reliable and accurate perception of the world.
Thalamic inputs and cortical microcircuitry underlying the functional architecture of the visual cortex. This project seeks to reveal the fundamental circuitry of the visual cortex that enables visual perception. Such understanding is essential not only for explaining many perceptual disturbances, but also for providing a neuronal basis for developing functionally useful prostheses for the blind.
One of the main trends in the evolution of the primate brain was the huge expansion of the cortical areas devoted to visual processing. However, the exact role of individual areas remains highly controversial, making detailed physiological and anatomical studies in suitable primate models a key step to elucidating their function in the human brain. In this project, we will address the organization of a poorly known group of visual areas, which is located deep in a part of the brain called the in ....One of the main trends in the evolution of the primate brain was the huge expansion of the cortical areas devoted to visual processing. However, the exact role of individual areas remains highly controversial, making detailed physiological and anatomical studies in suitable primate models a key step to elucidating their function in the human brain. In this project, we will address the organization of a poorly known group of visual areas, which is located deep in a part of the brain called the interhemispheric fissure (the medial complex of visual areas). Preliminary evidence suggests that these areas may provide anatomical shortcuts linking vision, behavioural reactions, and emotion. Suppose, for example, that you are sitting outside reading. Although deep in concentration, you are still able to detect the sudden movement of an approaching object in your peripheral field of vision. In many cases you can react (e.g., by ducking , or raising your arms to protect the face) long before you register what the object actually is. An adrenaline rush often accompanies these quick motor reactions, implying a parallel activation of the autonomic nervous system. While the mechanism by which the brain promotes these quick reactions remains poorly understood, we believe that the medial complex of visual areas holds the key. The aim of this study is to map the anatomical framework underlying our ability to react to sudden stimuli in our peripheral visual field. Such work is fundamental for understanding the functional organization of the brain. It also has the potential to lay the groundwork for developments in areas of applied research, including medicine (e.g. the design of better rehabilitation strategies for people with brain damage) and the cognitive sciences (e.g. a better understanding of the factors that limit human responses to visual stimuli).Read moreRead less
Histamine and non-visual regulation of retinal signalling. This project is internationally competitive, asking basic biological questions about the brain and vision. Of direct national benefit, the new knowledge generated may alter the way we understand how vision works. Ultimately this knowledge may give insight into particular health issues, such as the persistence of visual memory in Post Traumatic Stress Disorder, and age related diseases such as Alzheimer's disease. Further this new kno ....Histamine and non-visual regulation of retinal signalling. This project is internationally competitive, asking basic biological questions about the brain and vision. Of direct national benefit, the new knowledge generated may alter the way we understand how vision works. Ultimately this knowledge may give insight into particular health issues, such as the persistence of visual memory in Post Traumatic Stress Disorder, and age related diseases such as Alzheimer's disease. Further this new knowledge will flow directly into the reputation of our major institutes of higher education and strengthen their place on the world stage. Through both CIs, this research will contribute to the education of both undergraduate and postgraduate science students at The University of Melbourne. Read moreRead less
A Functional Predictive Test For Age-related Macular Degeneration
Funder
National Health and Medical Research Council
Funding Amount
$532,500.00
Summary
Age-related macular degeneration (AMD) is the leading cause of blindness in our community. It is a progressive, late onset disease affecting central vision. Signs of disease are present in 15% of the population over 50 years with severe visual loss affecting increasing numbers in each subsequent decade. By 90 years 25% of people will have lost significant vision. There is no prevention, and treatment options are limited and have little impact on the rates of blindness. AMD causes enormous person ....Age-related macular degeneration (AMD) is the leading cause of blindness in our community. It is a progressive, late onset disease affecting central vision. Signs of disease are present in 15% of the population over 50 years with severe visual loss affecting increasing numbers in each subsequent decade. By 90 years 25% of people will have lost significant vision. There is no prevention, and treatment options are limited and have little impact on the rates of blindness. AMD causes enormous personal costs and places a massive burden on health resources. The high prevalence, anticipated increase in the ageing population and the limited treatment options, highlight the urgency with which research is required. The early clinical signs of AMD are yellow deposits called drusen, in the central retina (macula) and alteration in retinal pigmentation. As AMD progresses the macula is damaged either through atrophy (holes) or by growth of blood vessels. Currently, clinically accessible information about drusen and pigmentary changes are used to grade the severity of disease and predict the risk of progression to vision loss. This at risk group is recruited into prevention and intervention studies looking for new interventions. Such scoring of clinical characteristics currently underpins all clinical trials and epidemiological research in AMD. However this scheme is not without limitations, and results in an inexact correlation between clinical appearance and risk of blindness. We believe that a test of retinal function, (ability to see in the dark, to detect a faint light), will provide a better correlation for identifying patients at high risk of vision loss. We aim to test various aspects of retinal function (in both the light and dark and for moving and stationary objects) in subjects with early clinical signs of AMD, to identify parameters that will be more sensitive and specific predictors of risk of progression to visually devastating complications of AMD.Read moreRead less