Interaction Of Thalamic And Cortical Activity In The Primate Visual System
Funder
National Health and Medical Research Council
Funding Amount
$487,580.00
Summary
We recently discovered that a primitive part of the visual pathway shows rhythmic nerve cell activity similar to slow brain waves recorded in sleep, anaesthesia, and epilepsy. We now plan to discover whether these primitive cells help to generate brain waves by measuring the timing of their activity together with brain waves in different visual and non-visual parts of the brain. This project will contribute to understanding the role of brain waves in normal brain function and epilepsy.
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
Generation Of Complex Responses In Retinal Ganglion Cells
Funder
National Health and Medical Research Council
Funding Amount
$490,500.00
Summary
The retinal ganglion cells, whose axons form the optic nerve, comprise numerous distinct types, which respond to visual stimuli in either a simple or complex manner. The project will investigate how the complex responses of the direction-selective ganglion cells (DSGCs) and the local-edge-detector ganglion cells (LEDs) are generated. It appears that the retinal neurons providing inhibitory input to DSGCs and LEDs use different neurotransmitters, and the project will investigate how this shapes t ....The retinal ganglion cells, whose axons form the optic nerve, comprise numerous distinct types, which respond to visual stimuli in either a simple or complex manner. The project will investigate how the complex responses of the direction-selective ganglion cells (DSGCs) and the local-edge-detector ganglion cells (LEDs) are generated. It appears that the retinal neurons providing inhibitory input to DSGCs and LEDs use different neurotransmitters, and the project will investigate how this shapes the response properties of the ganglion cells. This will be done both by recording the visually evoked responses of the ganglion cells in an isolated preparation of the retina and by using two-photon laser-scanning microscopy to functionally image the neuronal interactions between the neurons that inhibit the DSGCs.Read moreRead less
Organization Of Descending Auditory Projections From Inferior Colliculus To Cochlear Nucleus
Funder
National Health and Medical Research Council
Funding Amount
$473,121.00
Summary
Sensory information gains awareness by ascending brain pathways to reach consciousness. Descending projections, however, have grown in importance because of implications for feedback management of ascending signals. Studies of these pathways will provide insight into auditory processing with respect to selective volume control, calibration adjustments between the two ears, and the extraction of signals from background noise. The data could lead to new strategies for treating hearing disorders.
In the areas of the brain where visual information is processed, cells respond to the presentation of visual stimuli by changing their pattern of electrical activity. At the first level of analysis, the primary visual cortex (V1), individual cells become active only if line segments or borders of a particular orientation are present in their field of detection, which encompasses a small part of the visual scene. Cells in other visual cortical areas (the extrastriate cortex) perform more complex ....In the areas of the brain where visual information is processed, cells respond to the presentation of visual stimuli by changing their pattern of electrical activity. At the first level of analysis, the primary visual cortex (V1), individual cells become active only if line segments or borders of a particular orientation are present in their field of detection, which encompasses a small part of the visual scene. Cells in other visual cortical areas (the extrastriate cortex) perform more complex detection tasks in comparison with those in V1, which demand integration of information coming from much larger portions of the visual scene. One example of these more complex properties is the phenomenon of long-range contour integration, where our visual system groups individual line segments having similar orientations, so that they are perceived as part of the same contour. This property is reflected in the electrical responses of cells in the dorsomedial visual area (DM). How are properties such as orientation specificity and long-range contour integration created? To begin addressing this question, we will investigate correlations between the physiological properties of identified cells, the spatial distribution of their information collecting regions (dendrites), and the anatomical pathways by which they receive information from other parts of the brain. This is a basic science study aimed at determining the extent to which the anatomical structure of the brain helps define the function of individual cells and brain areas. Its primary benefit will be to increase our understanding of the mechanisms underlying all sensory processing in the brain. The knowledge obtained may also lead to developments in areas of applied research including medicine and cognitive science (for example, understanding how the brain learns to interpret visual information in early life, and how visual processing degrades with ageing).Read moreRead less