This article shows an optimized procedure for imaging of the neural substrates of auditory stimulation in the songbird brain using functional Magnetic Resonance Imaging (fMRI). It describes the preparation of the sound stimuli, the positioning of the subject and the acquisition and subsequent analysis of the fMRI data.
The neurobiology of birdsong, as a model for human speech, is a pronounced area of research in behavioral neuroscience. Whereas electrophysiology and molecular approaches allow the investigation of either different stimuli on few neurons, or one stimulus in large parts of the brain, blood oxygenation level dependent (BOLD) functional Magnetic Resonance Imaging (fMRI) allows combining both advantages, i.e. compare the neural activation induced by different stimuli in the entire brain at once. fMRI in songbirds is challenging because of the small size of their brains and because their bones and especially their skull comprise numerous air cavities, inducing important susceptibility artifacts. Gradient-echo (GE) BOLD fMRI has been successfully applied to songbirds 1-5 (for a review, see 6). These studies focused on the primary and secondary auditory brain areas, which are regions free of susceptibility artifacts. However, because processes of interest may occur beyond these regions, whole brain BOLD fMRI is required using an MRI sequence less susceptible to these artifacts. This can be achieved by using spin-echo (SE) BOLD fMRI 7,8 . In this article, we describe how to use this technique in zebra finches (Taeniopygia guttata), which are small songbirds with a bodyweight of 15-25 g extensively studied in behavioral neurosciences of birdsong. The main topic of fMRI studies on songbirds is song perception and song learning. The auditory nature of the stimuli combined with the weak BOLD sensitivity of SE (compared to GE) based fMRI sequences makes the implementation of this technique very challenging.
In this report, we describe an optimized protocol for the detailed in vivo characterization of neural substrates of auditory stimulation in anaesthetized zebra finches.
In line with the presented protocol, the majority of functional brain activation studies in animals using BOLD fMRI, anaesthetize the animals during the acquisition. Training animals to accustom them to the magnet environment and the scanner noise during the study periods is also possible but rather time-consuming and …
The authors have nothing to disclose.
This research was supported by grants from the Research Foundation – Flanders (FWO, project Nr G.0420.02 and G.0443.11N), the Hercules Foundation (grant Nr AUHA0012), Concerted Research Actions (GOA funding) from the University of Antwerp, and partly sponsored by EC – FP6 project DiMI, LSHB-CT-2005-512146 and EC – FP6 project EMIL LSHC-CT-2004-503569 to A.VdL. G.DG and C.P. are Postdoctoral Fellows of the Research Foundation – Flanders (FWO).
Name of the reagent/equipment | Company | Catalogue number | Comments |
Isoflurane anaesthetic | Isoflo | 05260-05 | |
PC-Sam hardware/software | SA-Instruments | http://www.i4sa.com | |
Monitoring and gating system | 1025 | ||
MR-compatible small rodent heater system | Model 1025 compatible | ||
Rectal temperature probe | RTP-102B | 7”, 0.044” | |
7T MR scanner | Bruker Biospin | PHS 70/16 | |
Paravision software | 5.1 | ||
Gradient Insert | BGA9S | 400 mT/m, 300A, 500V | |
Gradient Amplifiers | Copley Co., USA | C256 | |
Transmit resonators | Inner diameter: 72 mm, transmit only, active decoupled | ||
Receiver antenna – 20 mm quadrature Mouse Head | Receive only, active decoupled | ||
WaveLab software | Steinberg | ||
Praat software | Paul Boersma, University of Amsterdam | http://www.praat.org | |
Non-magnetic dynamic speakers | Visation, Germany | HK 150 | |
Fiber optic microphone | Optoacoustics, | Optimic 1160 | |
Sound amplifier | Phonic corporation | MM 1002a | |
Presentation software | Neurobehavioral Systems Inc. | ||
MRIcro | Chris Rorden | http://www.cabiatl.com/mricro/mricro/ | |
Statistical Parametric Mapping (SPM) | Welcome Trust Centre for Neuroimaging | 8 | http://www.fil.ion.ucl.ac.uk/spm/ |