The authors would like to acknowledge the contributions of Kyle Gilbert, who designed the custom RF coil, and Kevin Barker, who designed the MRI-compatible sled. This work was supported by the Canadian Institutes of Health Research (CIHR), Natural Sciences and Engineering Research Council of Canada (NSERC), and Canada Foundation for Innovation (CFI).

The following procedure can be applied to any imaging experiment in which anesthetized cats are used. Steps which are specifically required for auditory experiments (steps 1.1-1.7, 2.8, 4.1) can be modified to accommodate other sensory stimulus protocols.
All experimental procedures received approval from the Animal Use Subcommittee of the University Council on Animal Care at the University of Western Ontario and followed the guidelines specified by the Canadian Council on Animal Care (CCAC)<s...

The authors declare no conflicts of interest, financial or otherwise.

In designing an fMRI experiment for an anesthetized animal model of auditory function, the following issues should be given careful consideration: (i) the impact of anesthesia on cortical responses, (ii) the effect of background scanner noise, and (iii) the optimization of the data collection phase of the experimental procedure.
While an anesthetized preparation offers the important advantage of producing a prolonged period of sedation and minimizing potential head motion during a functional i...

Current understanding of auditory processing in mammals is mainly derived from invasive electrophysiological studies in monkeys1-5, ferrets6-10, bats11-14, rodents15-19, and cats20-24. Electrophysiological techniques commonly utilize extracellular microelectrodes to record the activity of single and multiple neurons within a small area of neural tissue surrounding the electrode tip. Established functional imaging methods, such as optical imaging and functional magnetic resonance imaging (fMRI), serve as useful complements to extracellular recordings by providing a macroscopic perspective of simultaneous driven activity across multiple, spatially distinct regions of the brain. Intrinsic signal optical imaging facilitates visualization of evoked activity in the brain by measuring activity-related changes in the reflectance properties of surface tissue while fMRI utilizes the blood-oxygen level-dependent (BOLD) contrast to measure stimulus-evoked hemodynamic changes in brain regions which are active during a particular task. Optical imaging requires direct exposure of the cortical surface to measures changes in surface tissue reflectance that are related to stimulus-evoked activity25. In comparison, fMRI is noninvasive and exploits the paramagnetic properties of deoxygenated blood to measure both cortical surface26-28 and sulcus-based27,29 evoked activity within an intact skull. Strong correlations between the BOLD signal and neuronal activity in nonhuman primate visual cortex30 and in human auditory cortex31 validate fMRI as a useful tool to study sensory function. Since fMRI has been used extensively to study features of the auditory pathway such as tonotopic organization32-36, lateralization of auditory function37, patterns of cortical activation, identification of cortical regions38, effects of sound intensity on auditory response properties39,40, and characteristics of the BOLD response time course29,41 in human, monkey, and rat models, the development of a suitable functional imaging protocol to study auditory function in the cat would provide a useful complement to the functional imaging literature. While fMRI has also been used to explore various functional aspects of the visual cortex in the anesthetized cat26-28,42, few studies have used this technique to examine sensory processing in cat auditory cortex. The purpose of the present protocol is to establish an effective method of using fMRI to quantify function in the auditory cortex of the anesthetized cat. The experimental procedures outlined in this manuscript have been successfully used to describe the features of the BOLD response time course in the adult cat auditory cortex43.

<table border="1">
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 <td></td>
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 <td>Material</td>
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 <td>Atropine sulphate injection 0.5 mg/mL</td>
 <td>Rafter 8 Products</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>Acepromazine 5 mg/mL</td>
 <td>Vetoquinol Inc.</td>
 <td></td>
 <td></td>
 </tr>
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 <td>Ketamine hydrochloride 100 mg/mL</td>
 <td>Bimeda-MTC</td>
 <td></td>
 <td></td>
 </tr>
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 <td>Dexmedetomidine hydrochloride (Dexdomitor 0.5 mg/mL)</td>
 <td>Orion Pharma</td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td>Isoflurane 99.9%</td>
 <td>Abbott Laboratories</td>
 <td></td>
 <td></td>
 </tr>
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 <td>Lidocaine (Xylocaine endotracheal 10 mg/metered dose)</td>
 <td>Astra Zeneca</td>
 <td></td>
 <td></td>
 </tr>
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 <td>Lubricating opthalmic ointment (Refresh Lacri Lube)</td>
 <td>Allergan Inc.</td>
 <td></td>
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 </tr>
 <tr>
 <td>Saline 0.95%</td>
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 <td>IV Catheter 22g (wings)</td>
 <td></td>
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 <td>IV Extension Set</td>
 <td>Codan US Corp.</td>
 <td>BC 269</td>
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 <td>IV Administration Set 10 drips/mL</td>
 <td></td>
 <td></td>
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 <td>Endotracheal tube 4.0</td>
 <td></td>
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 <td>Heating pads (Snuggle Safe)</td>
 <td>Lenric C21 Ltd.</td>
 <td></td>
 <td></td>
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 <td>Syringe 60 mL</td>
 <td></td>
 <td></td>
 <td></td>
 </tr>
 <tr>
 <td></td>
 <td></td>
 <td></td>
 <td>Equipment</td>
 </tr>
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 <td>External sound card</td>
 <td>Roland Corporation</td>
 <td>Cakewalk UA-25EX</td>
 <td></td>
 </tr>
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 <td>Stereo power amplifier</td>
 <td>Pyle Audio Inc.</td>
 <td>Pyle Pro PCAU11</td>
 <td></td>
 </tr>
 <tr>
 <td>MRI-compatible insert earphone system</td>
 <td>Sensimetric Corporation</td>
 <td>Model S14</td>
 <td></td>
 </tr>
 <tr>
 <td>Foam ear tips for insert earphones</td>
 <td>E-A-R Auditory Systems</td>
 <td>Earlink 3B</td>
 <td></td>
 </tr>
 <tr>
 <td>End-tidal CO2 monitor</td>
 <td>Nellcor&nbsp;</td>
 <td>N-85</td>
 <td></td>
 </tr>
 <tr>
 <td>MRI-compatible pulse oximeter</td>
 <td>Nonin Medical Inc.</td>
 <td>Model 7500</td>
 <td></td>
 </tr>
 <tr>
 <td>Syringe pump</td>
 <td>Harvard Apparatus</td>
 <td>70-2208</td>
 <td></td>
 </tr>
 </tbody>
 </table>

functional imaging of auditory cortex in adult cats using high-field fmri

Current knowledge of sensory processing in the mammalian auditory system is mainly derived from electrophysiological studies in a variety of animal models, including monkeys, ferrets, bats, rodents, and cats. In order to draw suitable parallels between human and animal models of auditory function, it is important to establish a bridge between human functional imaging studies and animal electrophysiological studies. Functional magnetic resonance imaging (fMRI) is an established, minimally invasive method of measuring broad patterns of hemodynamic activity across different regions of the cerebral cortex. This technique is widely used to probe sensory function in the human brain, is a useful tool in linking studies of auditory processing in both humans and animals and has been successfully used to investigate auditory function in monkeys and rodents. The following protocol describes an experimental procedure for investigating auditory function in anesthetized adult cats by measuring stimulus-evoked hemodynamic changes in auditory cortex using fMRI. This method facilitates comparison of the hemodynamic responses across different models of auditory function thus leading to a better understanding of species-independent features of the mammalian auditory cortex.

Representative functional data were acquired in a 7T horizontal bore scanner and analyzed using the Statistical Parametric Mapping toolbox in MATLAB. Robust cortical hemodynamic responses to auditory stimulation have consistently been observed in cats using the described experimental protocol43. Figure 6 illustrates the BOLD activation in 2 animals in response to a 30 sec broadband noise stimulus presented in a block design. T-statistic maps of the broadband noise vs. baseline (no stimulus) co...

Watch this Scientific Journal Video about Functional Imaging of Auditory Cortex in Adult Cats using High-field fMRI at JoVE.com

Functional Imaging of Auditory Cortex in Adult Cats using High-field fMRI

Functional studies of the auditory system in mammals have traditionally been conducted using spatially-focused techniques such as electrophysiological recordings. The following protocol describes a method of visualizing large-scale patterns of evoked hemodynamic activity in the cat auditory cortex using functional magnetic resonance imaging.

Current knowledge of sensory processing in the mammalian auditory system is mainly derived from electrophysiological studies in a variety of animal ...

functional-imaging-auditory-cortex-adult-cats-using-high-field

Research

JoVE Journal

Neuroscience

11.4K vues.  University of Western Ontario.  Les études fonctionnelles du système auditif chez les mammifères ont toujours été menées en utilisant des techniques spatialement ciblées telles que des enregistrements électrophysiologiques. Le protocole suivant décrit une méthode de visualisation des modèles à grande échelle de l'activité hémodynamique évoquée dans le chat cortex auditif en utilisant l'imagerie par résonance magnétique fonctionnelle. 