Richard L. Hyson, Ph.D. - US grants

It is generally accepted that early experience is important for optimal development of the nervous system. Support for this notion stems largely from studies showing that sensory deprivation results in neuronal atrophy. During development, afferent input regulates the metabolic activity of postsynaptic neurons and is crucial for cell survival. The general aims of this proposal are to identify the signaling cascades by which afferent activity regulates the integrity of postsynaptic neurons. The model system used for these studies is the brain stem auditory system of the chick. Neurons in the cochlear nucleus, nucleus magnocellularis (NM), receive their sole excitatory input from the ipsilateral auditory nerve. Eliminating auditory nerve activity (e.g., by cochlea removal) results in death and atrophy of NM neurons. Activity-dependent changes in neuronal metabolism are observed within an hour after cochlea removal, and by 6 hrs, a subpopulation of neurons (approx. 30 percent) can be identified as those destined to die. The proposed experiments use both in vivo and in vitro methods to investigate the signaling cascades involved in determining the ultimate fate (life or death) of deafferented neurons. Three lines of research will be pursued. First, afferent regulation of genes, which are known to regulate cell death in other systems, will be explored in detail. Specifically, bcl-2 expression is up-regulated in a subpopulation of neurons by 6 hrs after deafferentation. Studies will determine the conditions necessary for the up-regulation of this gene, and the potential role of bcl-2 in regulating deafferentation-induced cell death. Second, the neurotransmitter receptors controlling an early activity- dependent effect in this system, the regulation of ribosomal integrity, will be more accurately defined. These studies will primarily focus on the role of metabotropic glutamate receptors. A final set of studies will explore normative features of a second neurotransmitter system, GABA, which is present in the brain stem auditory pathways. Avian brain stem auditory neurons have an unusual response to GABA, and the proposed studies will determine the mechanisms underlying this response. Additional experiments will describe a relatively uncharacterized population of GABAergic cells in this system.

DESCRIPTION (provided by applicant): One important goal of contemporary auditory neuroscience is to understand the changes in the central nervous system that follow deafness. Since interventions, such as cochlear implants, work on a nervous system that has had long-lasting deafness, it is important to understand the possible changes in the makeup of these surviving cells so as to optimize such interventions. A fruitful model system for exploring these changes has been the brain stem auditory system of the chick. Deafness results in rapid changes in avian cochlear nucleus neurons and the eventual death of 20-30% of these neurons. Rapid changes (within hours) are observed in specific proteins within these neurons. The proposed research seeks to further define the protein changes in cochlear nucleus neurons in the early hours following deafness. This will lead to a greater understanding of the competing death and survival mechanisms engaged in these neurons and may help develop targeted interventions to promote the survival of neurons. In addition, long-term adjustments to deafness will be evaluated in cells that survive this insult. Finally, the proposed research will investigate proteins that specifically interact with the ribosomes of deafened cochlear nucleus neurons that may contribute to the ultimate demise of these cells. PUBLIC HEALTH RELEVANCE: Deafness results in the death of neurons in the central nervous system. This process involves changes in proteins that contribute to competing death and survival pathways. This project will identify proteins involved in these pathways and specifically proteins that may be involved in ribosomal dysfunction. This may lead to targeted interventions that could promote neuronal survival in a number of conditions, such as neurodegenerative disease, as well as following deafness.

How does the brain create orderly sequences of behavior? The problem of serial order in behavior permeates human language, the ability to play a musical instrument, or any number of other activities where human or animal intent can only be effectively communicated if several behavioral gestures are chained together in a specific sequence. How the brain accomplishes this task is currently unknown. One approach is to use an animal model (a songbird, the zebra finch) in which the brain region responsible for the serial ordering of song syllables has been identified (called "HVC", the acronym is the proper name). This project will investigate the hypothesis that the serial ordering of song syllables is mapped across several spatially-arranged chains of HVC neurons. This hypothesis is based on preliminary data indicating that HVC neural activity is largely confined to a single spatial axis during singing. Experiments will delineate the spatial organization of connections and electrophysiological properties of HVC neurons. Computational models based on the properties of HVC neurons will then be used to discover network configurations that produce orderly, sequential patterns of neural activity. Models will be validated with circuit-breaking experiments in behaving birds. Results will provide a first look at a network architecture used by an animal brain to create order and sequence in behavior, which in turn will provide a computational platform to understand how the process of learning new behavioral sequences utilizes or shapes such architectures. The research plan coordinates the activity of a faculty research team from three different academic departments (Psychology, Mathematics and Statistics), providing graduate and undergraduate students with access to the expertise of faculty researchers outside their home departments. Computational software tools as well as data from this project will be made available to the public at http://www.math.fsu.edu/~bertram/software/birdsong/ and at http://www.songbirdscience.com.

The purpose of this project is to elucidate how serial order is coded by the brain. If you were to read this sentence aloud, you would utter a precise, ordered sequence of over 50 distinct vocal sounds in less than 10 seconds. How does the brain store the individual sounds of speech and then coordinate the production of these sounds in a meaningful order so quickly? A similar question could be asked about the pianist performing a Mozart sonata, the songs of birds, or the mating dances of insects. How the brain stores these elaborate sequences of behavior remains unknown. Using the songbird zebra finch, a model organism that learns meaningful sequences of vocal sounds like humans do, the interdisciplinary research team will test the hypothesis that the brain encodes and stores sequences of behavior through two separate mechanisms that operate in parallel: one coding mechanism for the sequence of vocal sounds and one for the vocal sounds themselves. Given the diversity of animal species that display elaborate, meaningful sequences of behavior, the findings will influence understanding across a broad array of organisms, including humans. The research plan coordinates the activity of a faculty research team from four different disciplines (Neuroanatomy, Neurophysiology, Mathematics, and Statistics) and will provide students with a unique interdisciplinary training opportunity and environment.

Observed in nearly all animal forms (and exemplified by human speech) serial order in behavior consists of learning to organize a set of elemental gestural units into a purposeful sequence of action. Adult male zebra finches (Taeniopygia guttata) produce a highly quantifiable example of serial order in behavior (birdsong). Moreover, a premotor cortical region (HVC, proper name) is known to encode a consolidated premotor trace of song. Although consisting of similar cell types, the medial and lateral portions of HVC are hypothesized to encode the sequence (medial HVC) and syllables (lateral HVC) of song in parallel. The research team will test whether these two dimensions of song are encoded by physiological differences in 1) afferent input to medial and lateral HVC, or 2) the intrinsic network properties of medial and lateral HVC (or a combination of 1 and 2). However, parallel encoding of serial order in behavior should be hierarchical, with traces for sequence in a supervisory position over traces for elemental gestural units. The team will also test whether efferent axons emanating from medial and lateral HVC interact in a hierarchical fashion within vocal-motor cortex. Results will elucidate a network architecture for serial order in behavior and provide a computational platform to understand how learning new sequences shapes such memory architectures.

Many neuroscientists explain learning as a simple change in the number and/or strength of specialized connections between nerve cells called synapses. This research project tests a new idea, that learning also importantly involves molecular changes in other parts of nerve cells which control the production of electrical activity required for these cells to communicate with each other. Learning is studied in the context of how young songbirds learn to sing, which happens in a similar way to how humans learn to speak, play a musical instrument, or produce any complicated sequence of behavior. Using a combination of behavioral observation and recording together with anatomical, physiological, molecular, computational and statistical techniques, the research team will test the hypothesis that developmental singing changes are accompanied by changes in cell electrical activity that are not located at synapses. They will also identify the mechanistic basis for these electrical changes. This research will reveal important new details about how the brain can store learned information for an entire lifetime. It will also provide student research assistants with broad multidisciplinary training, as well as developing new analytical software and computational models that will benefit the broader neuroscience community (these will be made freely available through a publically-accessible web site). Neuroscience and mathematics videos tagged to specific State-mandated high school learning objectives will also be produced, which will be made available to teachers via a cataloged State portal. Finally, the research team conducts a wide variety of community education programs specifically related to neuroscience, birdsong, and learning. These activities include programs for K-12 schools as well as a scholarly course for senior citizens.

Much is known about the brain areas and circuits that underlie birdsong learning. Consequently, scientists know where to look for learning-induced changes (an area named HVC), but they do not know what neural changes encode the auditory memories of song. The proposed research tests the novel hypothesis that changes in specific, non-synaptic ionic currents in HVC neurons contribute to the encoding of auditory memories. Songbird auditory learning can be readily manipulated by controlling exposure to a tutor song. Preliminary data show that the intrinsic cell body/axonal channel properties of HVC neurons change in an experience-dependent manner during song development. The research team's recent characterization and modeling of the ionic currents that determine the physiology of HVC neurons in the adult finch now allow for the proposed developmental studies. Proposed studies will test hypotheses about the developmental emergence of specific ionic currents as they relate to sensory learning. This will lead to testable hypotheses about the underlying molecular mechanisms responsible for this learning. As part of this project, the team will also correct mistaken views about HVC of female zebra finches. Long thought to lack male-typical connectivity, new data show that female and male HVC have the same cell types and patterns of extrinsic connectivity. Since females show auditory learning of tutor song, but do not sing, analysis of female HVC will provide a critical test of the proposed hypotheses. Together, the proposed experiments will provide clues to fundamental questions about how early sensory information is stored as a stable memory trace that lasts a lifetime.