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High-Field Functional Imaging of Pitch Processing in Auditory Cortex of the Cat.

Butler BE, Hall AJ, Lomber SG - PLoS ONE (2015)

Bottom Line: Rather, cortical areas surrounding the posterior ectosylvian sulcus responded preferentially to the IRN stimulus when compared to narrowband noise, with group analyses revealing bilateral activity centred in the posterior auditory field (PAF).This study demonstrates that fMRI is useful for identifying pitch-related processing in cat cortex, and identifies cortical areas that warrant further investigation.Moreover, we have taken the first steps in identifying a useful animal model for the study of pitch perception.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada; Brain and Mind Institute, University of Western Ontario, London, Ontario, Canada.

ABSTRACT
The perception of pitch is a widely studied and hotly debated topic in human hearing. Many of these studies combine functional imaging techniques with stimuli designed to disambiguate the percept of pitch from frequency information present in the stimulus. While useful in identifying potential "pitch centres" in cortex, the existence of truly pitch-responsive neurons requires single neuron-level measures that can only be undertaken in animal models. While a number of animals have been shown to be sensitive to pitch, few studies have addressed the location of cortical generators of pitch percepts in non-human models. The current study uses high-field functional magnetic resonance imaging (fMRI) of the feline brain in an attempt to identify regions of cortex that show increased activity in response to pitch-evoking stimuli. Cats were presented with iterated rippled noise (IRN) stimuli, narrowband noise stimuli with the same spectral profile but no perceivable pitch, and a processed IRN stimulus in which phase components were randomized to preserve slowly changing modulations in the absence of pitch (IRNo). Pitch-related activity was not observed to occur in either primary auditory cortex (A1) or the anterior auditory field (AAF) which comprise the core auditory cortex in cats. Rather, cortical areas surrounding the posterior ectosylvian sulcus responded preferentially to the IRN stimulus when compared to narrowband noise, with group analyses revealing bilateral activity centred in the posterior auditory field (PAF). This study demonstrates that fMRI is useful for identifying pitch-related processing in cat cortex, and identifies cortical areas that warrant further investigation. Moreover, we have taken the first steps in identifying a useful animal model for the study of pitch perception.

No MeSH data available.


Related in: MedlinePlus

An anesthetized animal in the 8-channel RF coil.The head is surrounded by foam that serves to minimize movement and attenuate scanner noise. Also pictured is the intubation tube which permits the administration of isoflurane anesthesia.
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pone.0134362.g001: An anesthetized animal in the 8-channel RF coil.The head is surrounded by foam that serves to minimize movement and attenuate scanner noise. Also pictured is the intubation tube which permits the administration of isoflurane anesthesia.

Mentions: Ten adult (>6 months) domestic cats (Liberty Labs, Waverly, NY) participated in this experiment, and were housed as a clowder. All procedures were approved by the University of Western Ontario’s Animal Use Subcommittee of the University Council on Animal Care and were in accordance with the guidelines specified by the Canadian Council on Animal Care [17]. Normal hearing thresholds were verified for each animal using click-evoked auditory brainstem responses (ABRs) measured with an Eclipse EP15 Diagnostic ABR system (Interacoustics A/S, Denmark). Prior to each imaging session, cats were pre-medicated with a mixture of atropine (0.02 mg/kg s.c.) and acepromazine (0.02 mg/kg s.c.). This combination has been shown to reduce the amount of general anesthesia necessary during scanning [18], thus minimizing anesthetic-induced cortical suppression. Each animal was anaesthetized 20 minutes later with a cocktail of ketamine (4 mg/kg i.m.) and dexdomitor (0.025 mg/kg i.m.). Pilot studies in our lab comparing anesthetic regimes for functional imaging in the cat have identified this as the ideal combination of drugs to maintain adequate sedation for the duration of a scanning session while optimizing BOLD response. This procedure, described in length by Brown and colleagues [19] has been shown to be effective in demonstrating stimulus-evoked activity in the cat’s auditory cortex [19–20]. Once anesthetized, the animal was intubated and an indwelling catheter was placed in the saphenous vein to facilitate the maintenance of anesthesia. Once prepared, the animal was placed in a sternal position within a custom-built Plexiglas apparatus (Fig 1). Body temperature was maintained with heating discs placed inside the apparatus, and vitals including respiratory rate, end-tidal CO2, heart rate, non-invasive blood pressure, and blood-oxygen saturation were continuously monitored. MRI-compatible earphone inserts comprised of sound-attenuating foam surrounding a tube designed to deliver sound stimuli as closely as possible to the tympanic membrane were placed in the ear canals. The animals head was then placed inside a custom-built 8-channel radio frequency (RF) coil, and stabilized with sound dampening compression foam padding that further attenuated scanner noise. Finally, the animal and the Plexiglas apparatus were placed inside the bore of the magnet. For the remainder of the session, anesthesia was maintained through continuous administration of ketamine (0.6–0.75 mg/kg/hr i.v.) and spontaneous inhalation of isoflurane (0.4–0.5%). Following each scanning session, anesthesia was discontinued and animals were monitored until they recovered from anesthetic effects. The intubation tube was removed when the cat exhibited a gag reflex and increased jaw tone. Following successful recovery, the indwelling catheter was removed and cats were returned to their clowder. Every effort was made to minimize animal trauma during the entire scanning period.


High-Field Functional Imaging of Pitch Processing in Auditory Cortex of the Cat.

Butler BE, Hall AJ, Lomber SG - PLoS ONE (2015)

An anesthetized animal in the 8-channel RF coil.The head is surrounded by foam that serves to minimize movement and attenuate scanner noise. Also pictured is the intubation tube which permits the administration of isoflurane anesthesia.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4520558&req=5

pone.0134362.g001: An anesthetized animal in the 8-channel RF coil.The head is surrounded by foam that serves to minimize movement and attenuate scanner noise. Also pictured is the intubation tube which permits the administration of isoflurane anesthesia.
Mentions: Ten adult (>6 months) domestic cats (Liberty Labs, Waverly, NY) participated in this experiment, and were housed as a clowder. All procedures were approved by the University of Western Ontario’s Animal Use Subcommittee of the University Council on Animal Care and were in accordance with the guidelines specified by the Canadian Council on Animal Care [17]. Normal hearing thresholds were verified for each animal using click-evoked auditory brainstem responses (ABRs) measured with an Eclipse EP15 Diagnostic ABR system (Interacoustics A/S, Denmark). Prior to each imaging session, cats were pre-medicated with a mixture of atropine (0.02 mg/kg s.c.) and acepromazine (0.02 mg/kg s.c.). This combination has been shown to reduce the amount of general anesthesia necessary during scanning [18], thus minimizing anesthetic-induced cortical suppression. Each animal was anaesthetized 20 minutes later with a cocktail of ketamine (4 mg/kg i.m.) and dexdomitor (0.025 mg/kg i.m.). Pilot studies in our lab comparing anesthetic regimes for functional imaging in the cat have identified this as the ideal combination of drugs to maintain adequate sedation for the duration of a scanning session while optimizing BOLD response. This procedure, described in length by Brown and colleagues [19] has been shown to be effective in demonstrating stimulus-evoked activity in the cat’s auditory cortex [19–20]. Once anesthetized, the animal was intubated and an indwelling catheter was placed in the saphenous vein to facilitate the maintenance of anesthesia. Once prepared, the animal was placed in a sternal position within a custom-built Plexiglas apparatus (Fig 1). Body temperature was maintained with heating discs placed inside the apparatus, and vitals including respiratory rate, end-tidal CO2, heart rate, non-invasive blood pressure, and blood-oxygen saturation were continuously monitored. MRI-compatible earphone inserts comprised of sound-attenuating foam surrounding a tube designed to deliver sound stimuli as closely as possible to the tympanic membrane were placed in the ear canals. The animals head was then placed inside a custom-built 8-channel radio frequency (RF) coil, and stabilized with sound dampening compression foam padding that further attenuated scanner noise. Finally, the animal and the Plexiglas apparatus were placed inside the bore of the magnet. For the remainder of the session, anesthesia was maintained through continuous administration of ketamine (0.6–0.75 mg/kg/hr i.v.) and spontaneous inhalation of isoflurane (0.4–0.5%). Following each scanning session, anesthesia was discontinued and animals were monitored until they recovered from anesthetic effects. The intubation tube was removed when the cat exhibited a gag reflex and increased jaw tone. Following successful recovery, the indwelling catheter was removed and cats were returned to their clowder. Every effort was made to minimize animal trauma during the entire scanning period.

Bottom Line: Rather, cortical areas surrounding the posterior ectosylvian sulcus responded preferentially to the IRN stimulus when compared to narrowband noise, with group analyses revealing bilateral activity centred in the posterior auditory field (PAF).This study demonstrates that fMRI is useful for identifying pitch-related processing in cat cortex, and identifies cortical areas that warrant further investigation.Moreover, we have taken the first steps in identifying a useful animal model for the study of pitch perception.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada; Brain and Mind Institute, University of Western Ontario, London, Ontario, Canada.

ABSTRACT
The perception of pitch is a widely studied and hotly debated topic in human hearing. Many of these studies combine functional imaging techniques with stimuli designed to disambiguate the percept of pitch from frequency information present in the stimulus. While useful in identifying potential "pitch centres" in cortex, the existence of truly pitch-responsive neurons requires single neuron-level measures that can only be undertaken in animal models. While a number of animals have been shown to be sensitive to pitch, few studies have addressed the location of cortical generators of pitch percepts in non-human models. The current study uses high-field functional magnetic resonance imaging (fMRI) of the feline brain in an attempt to identify regions of cortex that show increased activity in response to pitch-evoking stimuli. Cats were presented with iterated rippled noise (IRN) stimuli, narrowband noise stimuli with the same spectral profile but no perceivable pitch, and a processed IRN stimulus in which phase components were randomized to preserve slowly changing modulations in the absence of pitch (IRNo). Pitch-related activity was not observed to occur in either primary auditory cortex (A1) or the anterior auditory field (AAF) which comprise the core auditory cortex in cats. Rather, cortical areas surrounding the posterior ectosylvian sulcus responded preferentially to the IRN stimulus when compared to narrowband noise, with group analyses revealing bilateral activity centred in the posterior auditory field (PAF). This study demonstrates that fMRI is useful for identifying pitch-related processing in cat cortex, and identifies cortical areas that warrant further investigation. Moreover, we have taken the first steps in identifying a useful animal model for the study of pitch perception.

No MeSH data available.


Related in: MedlinePlus