Timothy J. DeVoogd - US grants

The canary song system has proven to be a rich source of information on such general issues as neural sexual dimorphism, effects of steroids on brain development and function, adult neural plasticity, recovery of function, and lateralization. The proposed research will integrate behavioral observation, hormone manipulation, and sophisticated quantitative microanatomical techniques in adult canaries to further study these issues. The first two experiments study the behavioral and neuroanatomical consequences of experimentally preventing the normal fall drop in sex steroids. 1. If treatment with testosterone (T) prevents the neural regression and later song reorganization seen in untreated males, it would suggest that processing space in the neural network controlling song is limited: anatomical "erasure" of old circuits is necessary to permit the synaptic realignment which encodes the next year's song. 2. Lesions in left song control nuclei result in substantial song disruption. Recovery using the right hemisphere occurs the following spring. If T-treatment prevents this behavioral recovery, it would suggest that T can maintain lateralized function, and must be removed if there is to be any reorganization of function. Experiment three combines Golgi staining and electron microscopy to find and characterize new synapses in the adult. The P.I.'s computer-microscope system will be used to highlight sites of T-induced dendritic growth. Subsequent EM examination will indicate whether synapses on these new dendrites have a distinctive appearance, and if so, whether new synapses occur elsewhere on neurons from T-treated or control birds. Experiment four combines Golgi staining and autoradiography in order to characterize the song system neurons which derive from adult neurogenesis, and to determine whether endogenous steroids affect their differentiation or fate. Thus, does adult neurogenesis contribute significantly to rejuvenated capacity in the song system? These experiments study questions closely related to human health. Must neural regression occur for there to be forgetting? Are there circumstances under which some behavior must be forgotten in order to permit acquisition of another? Is reallocation of function (a mechanism for recovery from brain damage which also occurs in humans) facilitated by general neural regression in the damaged area? Can the morphology of new synapses and new neurons in an adult nervous system be used to predict conditions which augment their occurance and functional incorporation into a brain region?

Learning and remembering spatial relations is an important human capacity. Many lines of evidence suggest that the hippocampus is essential for this form of learning. However, much less is known of how spatial relations are encoded in the hippocampus or of how the hippocampus changes as learning of spatial relations occurs. This application will study the substrate for spatial learning using a novel animal model: seed storage in birds. Several species of birds hide large numbers of seeds and are able to retrieve them reliably weeks or months later. Several studies suggest that the hippocampus is necessary for the learning--it is larger in species that store than in related ones that do not, and birds that store are unable to retrieve if the hippocampus is lesioned. Experiments are proposed that will investigate the anatomical basis for the enhanced volume in species that store. This will suggest which aspects of the hippocampus have been augmented to permit this exceptional spatial ability. Other experiments will determine whether hippocampal anatomy in birds that store changes seasonally in phase with seasonal variation in the incidence of storage. If this were found, it would emphasize the extent to which the structure of complex neural networks can be modified in adulthood to allow for (or to encode) enduring changes in behavioral expression. Another experiment will determine whether short-term practice at storing and retrieving results in structural changes in the hippocampus. This experiment is designed so that storage and retrieval use one hemisphere, permitting within-animal comparisons of the consequences of learning. Differences in anatomy found in this experiment could point to sites and mechanisms used in spatial learning. It will be especially interesting to see whether any such changes are general or are focussed, perhaps in regions of the hippocampus that are enhanced in the birds that show the behavior. Together, these experiments assess this form of spatial learning at several levels. They search for network features related to the behavior, for long term structural change in the system related to changes in the frequency of the behavior, and for short term changes related to use. Each of these issues can be related to human spatial learning, its substrate and its capacity for change. The studies in this proposal will generate data that will be used to design a more complete program for investigating the neural substrate of spatial learning in this system.

9520730 Information is encoded in the brain by modifications in cellular structure and changes in numbers of synaptic connections between neurons. The brain is organized into discrete neural circuits which process specific types of learned information and control specific behaviors. When the connections (synapses) within these neural circuits are altered, the output of the circuit changes and the behavior that it controls is modified. The objective of this research is to increase understanding of the development of a learned behavior and the neural circuitry which controls that behavior. The development of one naturally occurring learned behavior, bird song, will be related to the development of synapses within specific song-related brain areas. Song in birds is a complex learned behavior that is controlled by a highly localized system of interconnected neurons. Synapse numbers in song-related brain areas of normally raised individuals and of individuals that have had no opportunity for song learning will be quantified using high magnification electron microscopy. The singing behavior and social behavior of both groups will be analyzed to correlate neuroanatomical and behavioral changes. Preliminary data indicate that song-deprived individuals possess approximately 40% more synapses than normally raised individuals. This may indicate that song learning is accompanied by a large scale reduction in synapse numbers. This research will increase our understanding, not just of the neural basis for song learning, but of principles and mechanisms important for many different forms of learning in different species of animals.

Learning and remembering spatial relations is an important human capacity. Many lines of evidence suggest that the hippocampus is essential for this form of learning, both in humans and in animals. However, much less is known of how spatial relations are encoded in the hippocampus or of how the hippocampus changes as learning of spatial relations occurs. This application will study the substrate for spatial learning using a novel animal model: seed storage in birds. Several species of birds hide large numbers of seeds and are able to retrieve them reliably weeks or months later. Several studies suggest that the hippocampus is necessary for the learning--it is larger in species that store than in related ones that do not, and birds that store are unable to retrieve if the hippocampus is lesioned. The P.I. and colleagues recently showed that the volume of the avian hippocampus increases in juveniles with the onset of storage and retrieval, and fluctuates seasonally in adults with use of seed storage and retrieval. This demonstrates that the structure of this complex neural network can be modified in adulthood to allow for (or to encode) spatial learning. Experiments in the present proposal build on this finding. One series of experiments will compare neuronal morphology and connectivity is species that store and species that do not, to determine whether the augmented volume in storing species is due to increases in a particular constituent of the hippocampus, and whether it is focused on particular regions of the hippocampus. These studies provide detailed neuroanatomy not yet available for this system and may suggest sites or features likely to be especially important for the learned behavior. A second series will determine whether subdivisions of the hippocampus are especially important for storage or for retrieval by either temporarily inactivating portions of the hippocampus or by looking for sites of expression of the immediate early gene c-fos with storage or retrieval. These experiments are designed to separate effects of memory consolidation from memory retrieval. A final series will measure long-term morphological consequences of manipulating experience with spatial learning in adult birds. This will help determine whether the increase in hippocampal volume previously observed permits spatial learning or is caused by it. This proposal assesses several major issues about the neurobiology of avian spatial learning. It searches for network features related to the behavioral capacity, for long term structural change in the system related to seasonal changes in the frequency of the behavior, and for short term changes related to use. Each of these issues is closely related to human spatial learning, its neural substrate and its capacity for change.

Research in South Africa will complement the candidate's ongoing exploration of structure-function relations int he brain. The investigator proposes to extend his recent findings that systematically relate avian brain structure, across species and within species, to capacity for song learning. In these studies, associations between brain nucleus morphology and characteristics of song provide a novel approach to identifying nucleus function. The investigators will look for these associations across many bird species: across families, across species within a genus, and across individuals within a species. A unique focus will be to study the brains of females in which mate selection uses song perception. The investigators' current data demonstrate the power of this approach in Acrocephalus species that breed in eastern Europe, some of which migrate to subsaharan Africa. Access to Acrocephalus species with distinct song characteristics that breed in Africa is essential to extend the investigators' initial work on the song system. Work with these species will also allow them to apply this approach to another behavioral system, to take these studies to spatial memory in birds beyond the lab to a natural behavior. They will compare hippocampal anatomy in species that do and do not migrate. Finally, to complete any of these studies, they must establish phylogenetic relationships between species by analyses of mitochondrial DNA. All aspects of this work will involve close collaboration with experts in avian systematics at the Fitzpatrick Institute of African Ornithology, University of Cape Town, over the course of three visits, one (6 months) to identify study sites, work out molecular procedures, and begin taping males, and two later (3-month) visits during reproduction to record and catch additional species. Issues of motor and spatial learning, and of sex differences and individual health. Comparative study may give new insights in neural features associates with each.

This proposal will study neural and behavioral correlates of auditory learning using song in songbirds. Song learning occurs during a sensitive period early in development, and a song derived from what was learned is produced by male songbirds throughout adult life. Song is a mode of communication, in which the receiver must be able to decode the message of the sender. In many species, males sing to females. While much is known of conditions for song acquisition and of the neural system which supports song production in males, little is known of song perception in general and, in particular, of how the brains of females learn about, process and respond to song. The experiments in this proposal use complementary behavioral, anatomical and functional methods to study the role of early experience in development of song perception and its neural substrate in females. They also assess whether brain effects of abnormal early experience can be reversed by providing appropriate experience to older animals.
The experiments will address important issues in neurobiology. First, does learning during early "sensitive" periods use the same brain mechanisms as later, more conventional learning? Second, which brain areas are used for complex auditory learning? Related to this, are the changes in these areas more evident in females than in males (since the females make decisions based on this information that seem more precise than decisions made by males)? Third, are the effects of this early learning (or lack of it) permanent, or can the information (and the brain areas that store it) be modified later on? Female songbirds are an ideal system in which to study these issues.

DESCRIPTION: (Adapted from applicant's abstract): Learning and remembering spatial relations is an important human capacity. Many lines of evidence suggest that the hippocampus is essential for this form of learning, both in humans and in animals. However, much less is known of how spatial relations are encoded in the hippocampus or of how the hippocampus changes as learning of spatial relations occurs. This application will study the substrate for spatial learning using a novel animal model: seed storage in birds. Several species of birds hide large numbers of seeds and are able to retrieve them reliably weeks or months later. Several studies suggest that the hippocampus is necessary for the learning--it is larger in species that store than in related ones that do not, and birds that store are unable to retrieve if the hippocampus is lessoned. The P.I. and colleagues showed that the volume of the avian hippocampus increases in juveniles with the onset of storage and retrieval, and fluctuates seasonally in adults with use of seed storage and retrieval. This demonstrates that the structure of this complex neural network is modified in adulthood to allow for (or to encode) spatial learning. Furthermore, inactivating the hippocampus disrupts retrieval based on spatial cues. Experiments in the present proposal build on these findings. One series of experiments will measure changes in the structure and projections of hippocampal neurons from spring to fall, as the birds increase their storage and retrieval. Plastic changes in anatomy will be compared to observations in a species that does not store food. We will try to determine the cause for the fall changes in behavior and neuroanatomy. A second series of experiments will examine hippocampal functioning. Two experiments will impair neuronal activity and look for changes in spatial learning or recall. A third will use immediate early gene expression as a marker of the neuronal activity associated with recall of spatial memories. It is intended to determine whether retrieving recent and remote spatial memories activates the same neural substrate. This proposal assesses several major aspects of the neurobiology of avian spatial learning. It searches for structural features related to the behavioral capacity, for long term structural change in the system related to seasonal changes in the frequency of the behavior, and for short term changes related to use. Each of these issues is closely related to human spatial learning, its neural substrate and its capacity for change.