The synaptic mechanisms that underlie the brain's remarkable capacity for learning remain unclear. One new model predicts that the acquisition and storage of learned skills involves the experience-driven clustering of co-active synapses onto short lengths of dendrite. Direct evidence for this synaptic clustering hypothesis is scant. This research proposal describes the first comprehensive tests of the model, to be provided by quantitative analysis of microanatomical changes in the barn owl auditory localization pathway. We recently showed that auditory-visual learning in juvenile owls involves selective adjustments in synaptic clustering on the dendrites of space-specific neurons, located within the inferior colliculus. In the first two sets of experiments we will determine whether similar changes occur in adults. Using multiple paradigms we will examine changes related both to the re-expression of normal circuitry and the acquisition of novel circuitry. The results will reveal the extent to which normal, enhanced and incremental training paradigms engage the synaptic clustering mechanism. In the third set of experiments we will examine a separate prediction of the model, whether non co-active synapses segregate on dendrites. The final set of experiments is designed to provide validation of these results at 'anatomical ground truth.'Specifically, we will use a newly developed high throughput method for serial section transmission electron microscopy to reconstruct the complete wiring diagram of the normal and learned circuits. These novel connectomes will be useful both for addressing the hypothesis-driven aims of this grant and for discovery-based approaches. Collectively, our experiments promise to reveal basic principles of synaptic reorganization that underlie the normal development and plasticity of sensory circuits, in both juvenile and adult brains. Such knowledge should prove invaluable for the long-term development of therapies aimed at the remediation of learning disorders.

Public Health Relevance

The brain possesses a remarkable capacity for learning, yet our understanding of the underlying biological mechanisms remains primitive. This proposal is aimed at testing a new theory for how synapses - the functional connections between nerve cells - reorganize as individuals learn new skills and recall them later in life. Knowledge of these mechanisms should prove invaluable for the eventual development of strategies to treat a wide spectrum of learning disorders.

National Institute of Health (NIH)
National Institute on Deafness and Other Communication Disorders (NIDCD)
Research Project (R01)
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Application #
Study Section
Auditory System Study Section (AUD)
Program Officer
Platt, Christopher
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University of California Davis
Schools of Medicine
United States
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McBride, Thomas J; DeBello, William M (2015) Input clustering in the normal and learned circuits of adult barn owls. Neurobiol Learn Mem 121:39-51
DeBello, William M; McBride, Thomas J; Nichols, Grant S et al. (2014) Input clustering and the microscale structure of local circuits. Front Neural Circuits 8:112
Pena, Jose L; DeBello, William M (2010) Auditory processing, plasticity, and learning in the barn owl. ILAR J 51:338-52
Nichols, Grant S; DeBello, William M (2008) Bidirectional regulation of the cAMP response element binding protein encodes spatial map alignment in prism-adapting barn owls. J Neurosci 28:9898-909
McBride, Thomas J; Rodriguez-Contreras, Adrian; Trinh, Angela et al. (2008) Learning drives differential clustering of axodendritic contacts in the barn owl auditory system. J Neurosci 28:6960-73
DeBello, William M (2008) Micro-rewiring as a substrate for learning. Trends Neurosci 31:577-84
Swofford, Janet A; DeBello, William M (2007) Transcriptome changes associated with instructed learning in the barn owl auditory localization pathway. Dev Neurobiol 67:1457-77
Rodriguez-Contreras, Adrian; Liu, Xiao-Bo; DeBello, William M (2005) Axodendritic contacts onto calcium/calmodulin-dependent protein kinase type II-expressing neurons in the barn owl auditory space map. J Neurosci 25:5611-22