THE BRAIN OF BIRDS: A MODEL FOR THE STUDY OF COGNITIVE FUNCTIONS
Bird brains are of interest to neuroscientists in more ways than one. For example, the increasingly precise description of the structure and organization of brain areas involved in vocal control allows us to understand how birds sing. Or the discovery of the existence of an "optic flow regulator" helps to explain the control of altitude in birds in flight. The brain of birds is also used as a model to study emotionality. In the early 1990s, two lines of Japanese quail (Coturnix japonica) were selected for breeding: one is particularly emotional and has a relatively long duration of tonic immobility[1], while the other is less emotional and has a shorter duration of tonic immobility[2]. The comparison of these two lineages would benefit from a precise description of their brain anatomy and especially of their cerebral connectivities, data largely missing.
Diffusion MRI TO RECONSTITUTE NERVOUS FIBERS
Researchers from the UMR BAOBAB (NeuroSpin department), in collaboration with INRAE of Nouzilly, have established the first atlas of anatomical connectivity from 21 brains of male Japanese quails from both emotive and non-emotive lineages that were scanned post-mortem using an ultra-high field (11.7 T) preclinical MRI. Thanks to advanced methods of reconstructing the path of nerve fibers by diffusion MRI (tractography) and of grouping fibers (in fascicles), a new atlas was established which is composed of 34 white matter bundles reproducible between individuals and which correspond to real "places" where cerebral connections are concentrated (these are called connectivity hubs). Following the example of what has already been done for the human brain[3], this new atlas makes it possible to explore the diversity of the structural connectivity of the male Japanese quail. Moreover, it allows to automatically segment the white matter bundles of any new individual, and offers a unique tool to explore the functional networks in the male Japanese quail. This atlas has thus made it possible to specifically compare the structural connectivities of two Japanese quail lineages, and to show the existence of significant differences between the short tonic immobility and long tonic immobility lineages, in terms of the morphometry of their neuroanatomical structures, and of the connectivity between the anatomical structures involved in particular in the management of emotions and fear. This work paves the way for understanding the communication between anatomical structures in Japanese quail and provides an important tool for future studies of animal structural connectivity.
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