Developmental learning involves nonsynaptic plasticity

Florida State University, Tallahassee FL

Investigators

Abstract

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.