The Role Of Spectral Cues In Sound Localization By The Barn Owl Cells In Vitro

Author : Thomas J. McBride
Publisher :
ISBN 13 : 9781124907727
Total Pages : pages
Book Rating : 4.9/5 (77 download)

DOWNLOAD NOW!

Download or read book Microanatomical Changes to the Wiring Diagram of the Barn Owl Sound Localization Pathway During Development and Learning written by Thomas J. McBride and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the most remarkable properties of the brain is its capacity for learning. Accordingly, a major goal of neuroscience has been to understand the modifications to neural circuits that encode the acquisition of learned skills and memories. Recent discoveries have proposed that microanatomical changes to the brain's wiring diagram could play a central role in this process. There is an increasing amount of data from both experimental and modeling studies which support the notion that individual dendritic branches are the fundamental computational subunit of the brain. If this is correct, then experience-driven clustering of coactive synapses on to individual branches of dendrite would be a powerful mechanism for information storage. Here, I provide some of the first direct tests of this prediction. My experiments exploit a unique feature of the barn owl auditory localization pathway which permits retrospective analysis of prelearned and postlearned circuitry: owls reared wearing prismatic spectacles develop an adaptive microcircuit that coexists with the native one but can be analyzed independently based on topographic location. I use focal injections of tracer to label coactive axons, immunohistochemistry to label their target dendrites, and high-resolution confocal imaging to identify potential synapses. In prism-reared and normal juvenile owls, I found that clustering is bidirectionally adjustable and tuned by behaviorally relevant experience. Moreover, the microanatomical configurations of both juvenile experimental groups mirror the functional circuit strengths that were recorded in vivo. When prisms are removed from prism-adapted owls, they re-express a normal representation of auditory space while retaining an anatomical trace of the learned circuit. However, in adult owls, I found no difference in clustering across the different circuits. Rather, both adult groups display a high degree of clustering across all circuits, and fewer contacts per branch than found in juvenile owls. Thus, in adults, patterns of clustering in different zones do not mirror the functional strength of the circuit. Taken together, these results suggest that while in juveniles, clustering of co-active synapses may be a mechanism for the acquisition and storage of adaptive responses, a different mechanism must be responsible for adaptations that occur in adulthood. Finally, I test a new method, automated serial section transmission electron microscopy (ATEM), for dense reconstruction of large volumes of neural circuitry at synaptic resolution. ATEM promises to uncover the complete wiring diagram of the auditory localization pathway, and hence provide anatomical ground truth of how learning is encoded in the brain.