Auditory evoked BOLD responses in awake compared to lightly anaesthetized zebra finches

L Van Ruijssevelt,A Van Der Linden,M Verhoye,M T Van Gurp,J Hamaide

doi:10.1038/s41598-017-13014-x

Abstract

Functional magnetic resonance imaging (fMRI) is increasingly used in cognitive neuroscience and has become a valuable tool in the study of auditory processing in zebra finches, a well-established model of learned vocal communication. Due to its sensitivity to head motion, most fMRI studies in animals are performed in anaesthetized conditions, which might significantly impact neural activity evoked by stimuli and cognitive tasks. In this study, we (1) demonstrate the feasibility of fMRI in awake zebra finches and (2) explore how light anaesthesia regimes affect auditory-evoked BOLD responses to biologically relevant songs. After an acclimation procedure, we show that fMRI can be successfully performed during wakefulness, enabling the detection of reproducible BOLD responses to sound. Additionally, two light anaesthesia protocols were tested (isoflurane and a combination of medetomidine and isoflurane), of which isoflurane alone appeared to be the most promising given the high success rate, non-invasive induction, and quick recovery. By comparing auditory evoked BOLD responses in awake versus lightly anaesthetized conditions, we observed overall effects of anaesthetics on cerebrovascular reactivity as reflected in the extent of positive and negative BOLD responses. Further, our results indicate that light anaesthesia has limited effects on selective BOLD responses to natural versus synthetic sounds.

Highlights

Functional magnetic resonance imaging is currently one of the most important neuroimaging methods in cognitive neuroscience[1]
The acclimation procedure was based on a protocol which was previously applied to train pigeons to be scanned in awake conditions[16]
The procedure consisted of 3 consecutive phases: (1) Acclimation to body restraining in a dark scanner-like environment; (2) Acclimation to total restraint including head fixation; (3) Acclimation to total restraint and scanner noise (Fig. 1)

Summary

Introduction

Functional magnetic resonance imaging (fMRI) is currently one of the most important neuroimaging methods in cognitive neuroscience[1]. Different protocols have been proposed ranging from paralyzing the animals with curare-like drugs[2] to the use of special restraining devices combined with an acclimation procedure to accustom subjects to the imaging protocol (e.g.3–5) For ethical reasons, the latter method is usually preferred. The second goal of this study was to test two light anaesthesia protocols for zebra finch fMRI experiments and compare BOLD responses to auditory stimulation obtained in anaesthetized birds to those in awake birds. Two different anaesthetics were included: (i) isoflurane and (ii) medetomidine These agents have been previously used in auditory fMRI experiments in zebra finches[8,9,10,11,12] and are widely used in fMRI studies in other animal models[13,14]. We further refer to this anaesthesia protocol using the ‘Med/Iso’ acronym

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Conclusion