Exploring structural neuroplasticity in the zebra finch brain using in vivo MRI
4 May 2018
UAntwerp, Campus Drie Eiken, Building Q, Auditorium O3 - Universiteitsplein 1 - 2610 Wilrijk (Antwerp) (route: UAntwerpen, Campus Drie Eiken
5:00 PM - 7:00 PM
Annemie Van der Linden, Marleen Verhoye
PhD defence Julie Hamaide - Department of Biomedical Sciences
Proper knowledge of the fundamental features in control of neuroplasticity are highly necessary to understand how the brain matures, how basic sensory but also higher cognitive skills develop in early life, etc. A remarkable model to study developmental plasticity related to the acquisition of cognitive skills can be found in songbirds. In contrast to vocalisations uttered by most vertebrate species, songbirds sing acoustically complex songs that are learned and can be modified based on the social context. This remarkable skill, shared by only few species, has been used extensively as a model for human speech learning. Despite intensive efforts aimed at identifying the neural substrate in control of singing or implicated in auditory perception and due to a lack of brain-wide imaging tool capable of assessing the structural properties of the entire zebra finch brain, up to recently, research was almost exclusively directed at the song control and auditory system, or areas directly related to these pathways. Therefore, this thesis aimed at extending current views by (1) implementing in vivo Magnetic Resonance-based Imaging (MRI) tools that allow to map the structural properties of the entire zebra finch brain while (2) birds learn to sing or (3) recover from brain trauma.
First, we implemented appropriate MRI tools sensitive to capturing structural neuroplastic events of the entire brain at different spatial scales. We opted for Diffusion Tensor Imaging (DTI), a technique that infers microstructural tissue properties based on measuring the diffusion properties of water protons in tissues, and T2-weighted 3-dimensional (3D) anatomical scans that enable assessing overall gross neuroanatomy. The sensitivity of the optimized protocols was validated in a proof-of-principle study. Second, we employed these in vivo MRI tools to establish a spatio-temporal map of structural neuroplastic events taking place throughout and beyond the critical period for song learning, from 20 to 200 days post hatching. Surprisingly, we observed that the accuracy of song imitation correlated with the structural properties of distinct brain regions in the maturing male zebra finch brain. Third, we traced structural neuroplastic events in adult male zebra finch brains following neurotoxic lesioning of the striatal component of the song control circuitry and uncovered structural neuroplastic events in the cerebellum.
To conclude, this thesis initiates a novel framework that enables to longitudinally trace the structural properties of the songbird brain and relate structural neuroplastic events to age or performance using completely non-invasive MR-based in vivo imaging tools.