Dale Purves - US grants

Recent work in mammalian autonomic ganglia has shown that the number of axons that innervate these nerve cells is correlated with the configuration of the target neurons. Thus, neurons that lack dendrites are innervated by a single axon, whereas neurons that bear dendrites are innervated by a number of axons that is proportional to the complexity of the dendritic tree. These results suggest a novel role for neuronal dendrites, namely that they regulate the degree of convergent innervation of target neurons. They also raise a number of questions about the significance, development and regulation of dendritic arborizations. It is these issues that we now propose to explore. First, we will examine the factors that influence the generation of dendrites in mammalian autonomic ganglia; the purpose of this portion of the project is to understand how dendritic complexity is determined. Second, we will explore the numbers of pre- and postsynaptic nerve cells and the average degree of convergence and dendritic complexity in the cervical sympathetic system of five different mammals; the purpose of this part of the project is to assess the functional significance of different degrees of dendritic complexity and convergence. Third, we will explore the distribution of innervation arising from individual axons on particular target cells in mouse superior cervical ganglion; the purpose of this work is to assess how dendrites influence the apportionment of innervation to neurons more complex than the parasympathetic ganglion cells studied during the initial grant period. In sum, these specific aims are directed at understanding how neuronal dendrites are regulated, how dendrites control convergence, and how convergence influences the function of neural pathways. The reason for pursuing these issues in mammalian autonomic ganglia is that these accessible collections of neurons are simple enough so that some fundamental rules of innervation in the mammalian nervous system may be discerned.

Several lines of evidence indicate that neuronal connections in the mammalian nervous system are capable of substantial change. This evidence includes the normal rearrangement of synaptic connections during development, the continued capacity for synaptic rearrangement in response to experimental manipulation, and ultrastructural signs of physiological remodelling throughout life. The purpose of the experiments proposed here is to develop and apply several methods that will enable us to monitor the geometry of individual neurons for periods of up to a week or more in mammalian autonomic ganglia. Our more general aim is to obtain direct evidence about the way in which connections between mammalian nerve cells are regulated. The methods we will use include intracellular marking by a) concurrent injection of the fluorescent dye 6-carboxyfluorescein and horseradish peroxidase; b) injection of dextran labeled with fluorescein; and, c) supravital staining of nerve cells using intracellular peroxidase to catalyze the production of melanin from DOPA. The first two methods involve imaging neurons in vivo by SIT camera video intensification. The last approach may allow living neurons containing melanin to be observed repeatedly with conventional optics. Autonomic ganglia will be used for these studies because of their accessibility, and because we already know a great deal about the connections and development of these relatively simple collections of neurons. We believe, however, that the techniques and principles which may emerge from this work will be useful in understanding other more complex parts of the mammalian nervous system.

neural plasticity; neurobiology; autonomic ganglion; nervous system regeneration; glia; synapses; stainings; fluorescence microscopy; denervation;

The mammalian brain grows substantially in postnatal life. Despite wide recognition of this phenomenon, little attention has been paid to the cellular basis of ongoing brain growth. To what extent does this growth reflect the addition of new circuitry, and what role might such addition play in some of the major unexplained questions in developmental neurobiology? These enigmas include the basis of critical periods, the age-dependent response of the nervous system to injury, and the remarkable ability of the juvenile brain to store large amounts of new information. In order to successfully address these issues, the formation of novel circuitry in the developing brain must be observed and quantified by evaluating both individual neural elements (axonal branches, dendrites, synapses) and the development of entire circuits. Fortunately, the brains of many mammals comprise complex iterated circuits that can be studied by both morphological and electrophysiological methods. Examples are columns and "blobs" in the visual system, columns and "barrels" in the somatosensory system, glomeruli in the olfactory system, and cell islands and "striasomes" in the neostriatum. Using the developing brain of several different mammalian species --including man-- we will examine systematically the development of two such circuits, olfactory glomeruli and blobs in the primary visual cortex. Part of this work will be carried out using vital imaging, confocal microscopy and magnetic resonance microscopy to examine changes in the arrangement and number of these circuits over time in living animals. In other segments of the project we will use more conventional electrophysiological and morphological approaches to examine the differentiation of neuronal elements and synaptic connections within circuits. As argued in the body of the application, the information that we hope to gain about the postnatal construction of circuitry in the mammalian brain is likely to be of central importance to both basic neurobiology and to understanding human neural development.

The mammalian brain grows substantially in postnatal life. Despite wide recognition of this phenomenon, little attention has been paid to the cellular basis of ongoing brain growth. To what extent does this growth reflect the addition of new circuitry, and what role might such addition play in some of the major unexplained questions in developmental neurobiology? These enigmas include the basis of critical periods, the age-dependent response of the nervous system to injury, and the remarkable ability of the juvenile brain to store large amounts of new information. In order to successfully address these issues, the formation of novel circuitry in the developing brain must be observed and quantified by evaluating both individual neural elements (axonal branches, dendrites, synapses) and the development of entire circuits. Fortunately, the brains of many mammals comprise complex iterated circuits that can be studied by both morphological and electrophysiological methods. Examples are columns and "blobs" in the visual system, columns and "barrels" in the somatosensory system, glomeruli in the olfactory system, and cell islands and "striasomes" in the neostriatum. Using the developing brain of several different mammalian species --including man-- we will examine systematically the development of two such circuits, olfactory glomeruli and blobs in the primary visual cortex. Part of this work will be carried out using vital imaging, confocal microscopy and magnetic resonance microscopy to examine changes in the arrangement and number of these circuits over time in living animals. In other segments of the project we will use more conventional electrophysiological and morphological approaches to examine the differentiation of neuronal elements and synaptic connections within circuits. As argued in the body of the application, the information that we hope to gain about the postnatal construction of circuitry in the mammalian brain is likely to be of central importance to both basic neurobiology and to understanding human neural development.

DESCRIPTION: Previous studies from this lab provided evidence that postnatal brain development in olfactory and somatosensory cortices is mainly constructive, and that neural activity foments postnatal elaboration of circuitry. The present proposal addresses the question of why the brain adds enormous numbers of neuronal branches and synapses postnatally in an activity-dependent manner, especially since this entails jeopardy from the effects of deprivation. A review of the evidence in anthropoid primates suggests that the expression of ocular dominance columns in visual cortex is related to animal size. The first aim of the study is to confirm the validity of this 'size' principle among several carnivores and prosimians. The second aim is to determine whether the size principle results from differences in the duration of asynchronous binocular activity during development. This will be tested by 1) attempting to generate ocular dominance columns in animals which normally do not express them; and 2) directly following the formation and modulation of ocular dominance columns with optical imaging during development. A third aim will be to explore in humans the hypothesis the activity-dependent construction of the visual world serves to establish neural associations that allow a correct interpretation of an inherently ambiguous visual world (the consensus at the present is that activity acts primarily to validate and refine receptive field properties). This will entail an analysis of 1) the perception of transparent 3-D objects; and 2) the relationship between biases in the perception of oriented contours and the prevalence of differently oriented contours in the visual world. The results of these several projects should indicate whether the prolonged postnatal period of activity-dependent plasticity in mammals plays a largely permissive role, or whether it enables experience to make the visual associations that allow us to see normally.

DESCRIPTION (provided by applicant): A training program in neuroscience centered around the new Department of Neurobiology in the Medical Center was first established early in the early 1990's. Under the aegis of NIGMS support, the program has now expanded to include the breadth of training now afforded by the newly established Center for Cognitive Neuroscience and the Center for Brain Imaging and Analysis. The Center for Cognitive Neuroscience (CCN), under the direction of Dr. George R. Mangun (also a member of the Department of Neurobiology) presently offers only a Master's program. As part of a university-wide initiative, Cognitive Neuroscience will continue to grow, providing new opportunities for classroom and laboratory training in this aspect of neuroscience. By the same token, the new Brain Imaging and Analysis Center (BIAC) under the direction of Dr. Gregory McCarthy (who, like Mangun, is a member of the Department of Neurobiology) has grown rapidly since its inception three years ago. This initiative has also augmented our ability to train graduate students in this now central aspect of basic and clinical neuroscience. Like the CCN, the BIAC offers no specific graduate training program. Both Centers will join us this year in our recruitment and training effort, thus creating a comprehensive program that spans all aspects of molecular/cellular, systems and cognitive neuroscience. To reflect these changes we have altered the name of the program slightly by substituting the word 'neuroscience' for 'neurobiology.' The support from this training grant has been, and will continue to be, critical in maintaining and improving a program that has progressed from virtual non-existence a decade ago to one that is now ranked in the top 5 programs nationally. We are therefore seeking 10 predoctoral slots per year, which will allow us to carry 5 students for 2 years each.

DESCRIPTION (provided by applicant): Recent work has led to the hypothesis that the percepts generated by visual cortex are determined stochastically according to the success (or failure) of past behaviors in response to inevitably ambiguous retinal images. So far, the basis for this idea is indirect: psychophysical evidence shows that the images seen in response to a wide variety of stimuli accord with the probability distributions of the possible sources of the corresponding retinal image. These findings imply that the primary role of the visual cortical processing -- and by inference the role of sensory cortices generally -- is to instantiate and process the probability distributions of the possible stimulus sources. Here we propose to initiate a direct exploration of this novel concept of cortical function by taking advantage of the ease (and accuracy) with which visuotopic and orientation maps can be determined in the primary visual cortex (V1) by optically imaging patterns of cortical activity. Using this method, we propose to examine how geometrical target angles that elicit very different perceptions as a function of context are represented in an experimental animal (the tree shrew to begin with). The project entails three Specific Aims: 1) To determine with optical imaging of 'intrinsic signal' how simple angular stimuli are represented in VI of anesthetized animals, using both topographic and orientation maps as indices; 2) To determine the cortical representations of topography and orientation elicited by the same stimuli in contexts that markedly change the probability distributions of the possible sources (and thus perception); and 3) To examine whether awake behaving animals, much as human subjects, see the same geometrical stimuli differently as a function of contextual statistics. These experiments will show whether visuotopic and orientation maps represent image features (i.e., location in space and line orientation), as has long been thought, or whether, as we suspect, they represent the probability distributions of the possible sources of visual stimuli. Knowledge that the primary visual cortex operates in this probabilistic way would demand a reinterpretation of present structural and functional information about V1, and would strongly encourage further exploration of other sensory cortices using this framework.

With support from a National Science Foundation Major Research Insturmentation Award, Duke University's Pratt School of Engineering will acquire a fully enclosed, six-sided, 3m x 3m x 2.7m, back projected virtual reality environment. The VisRoom will be located in a specially constructed 30 foot cube in the atrium of the Center for Interdisciplinary Engineering, Medicine and Applied Science (CIEMAS). The VisRoom will be the only facility of its kind in the Southeast and the fourth such system in the United States.

As the datasets scientists collect increase in size and complexity, so increases the need for ever more powerful tools to support data analysis and scientific communication. The tools that in the past have proved most useful in this regard have been those that take advantage of the remarkable information-processing ability built into human perceptual systems, particularly vision and audition. Thus, investigators in many of the most innovative fields of research, e.g., proteomics, genomics, seismology, neuroscience and astrophysics, rely heavily on computationally-intensive visualization tools to explore their data and test models. Technologies such as the VisRoom are used not only to explore data collected through other means, but also as experimental tools in and of themselves for investigating the many aspects of human perception and motor control that remain poorly understood. The project directors anticipate that providing scientists from many disciplines with access to state-of-the-art visualization technologies will inspire them to find creative and productive ways of incorporating the new tools into their respective research programs.

Projects curently planned for this VisRoom include research in cognitive neuroscience, exploration of 3D structures, and education. Specifically, visual perception studies will take advantage of the VisRoom's ability to precisely control illumination, object reflectances, and scene geometry to assess how systematic manipulations chage the observers' perceptions of color. Movement studies will dynamically distort the visual field during reaching tasks to gain insight into the role of attention, movement planning, and movement execution. Computer scientists and biochemists will jointly use the VisRoom to 'crawl' between two proteins to inspect the interaction areas directly. Biomedical engineers who develop physiological models of the heart will use the VisRoom to 'enter' the heart wall and investigate the relationships among the different physiological processes that govern cardiac function. Finally, middle school students will use the VisRoom as an aid in the study of developmental biology. For example, they will have the opportunity to interact with a virtual developing chicken embryo and observe how, at 48 hours, the single tube of the artery system curves in 3D to form the four chambers of the heart. In addition to providing scientists and educators with a with a powerful new visualization tool, the project directors anticipate that the VisRoom will act as a "watering hole," supporting the kind of cross-disciplinary interaction that often opens up new areas of scientific research.

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).

For thousands of years humans have made music using specific tone collections called scales or modes that have a special aesthetic and emotional appeal (the familiar 'do,re, mi...' scale, for example). Since the time of Pythagoras, understanding the basis of these of this appeal has fascinated musicians, scientists, philosophers, linguists and many others. Although tonal relationships have been fully documented over the centuries, the basis of this phenomenology is not understood. Recent results from this group of investigators have indicated that musical tones are also embedded in the characteristics of speech, providing a way to explore issues at the intersection of music, language and aesthetics. Using and extending databases of music and speech, the investigators will examine 1) why humans favor a few particular tone collections out of the many billions that are possible; 2) why some tone combinations are more consonant than others; and 3) why major and minor scales or modes have distinct emotional effects. The hypothesis is that the answer in each case lies in the similarity of musical tones and the characteristics of human vocalization, leading to unconscious associations that determine the way musical tones are perceived.

Answering these questions would provide a major intellectual advance in the long history of work on the basis of musical tonality and its effects on listeners. The hypothesis that the answers lie in the similarity of the spectra generated by musical intervals and the spectra generated by the human voice is a promising way to examine these issues. Whereas numerous investigators in recent centuries have argued that music derives from speech, no one has explored this possibility in terms of spectral imitation. If it can be demonstrated that the tonal phenomena evident in music arise from similarity to speech, theoretical, experimental and practical work in audition, linguistics, psychoacoustics, phonetics, speech pathology, speech recognition, anthropology and philosophy may have a new way of understanding some very old problems.