Functional magnetic resonance imaging of the ascending stages of the auditory system in dogs

Abstract

BackgroundFunctional magnetic resonance imaging (fMRI) is a technique able to localize neural activity in the brain by detecting associated changes in blood flow. It is an essential tool for studying human functional neuroanatomy including the auditory system. There are only a few studies, however, using fMRI to study canine brain functions. In the current study ten anesthetized dogs were scanned during auditory stimulation. Two functional sequences, each in combination with a suitable stimulation paradigm, were used in each subject. Sequence 1 provided periods of silence during which acoustic stimuli could be presented unmasked by scanner noise (sparse temporal sampling) whereas in sequence 2 the scanner noise was present throughout the entire session (continuous imaging). The results obtained with the two different functional sequences were compared.ResultsThis study shows that with the proper experimental setup it is possible to detect neural activity in the auditory system of dogs. In contrast to human fMRI studies the strongest activity was found in the subcortical parts of the auditory pathways. Especially sequence 1 showed a high reliability in detecting activated voxels in brain regions associated with the auditory system.ConclusionThese results indicate that fMRI is applicable for studying the canine auditory system and could become an additional method for the clinical evaluation of the auditory function of dogs. Additionally, fMRI is an interesting technique for future studies concerned with canine functional neuroanatomy.

Regional brain activations in awake unrestrained dogs

“…Given the widespread interest, both general and scientific, in dog behavior, it is striking how little we know about brain function specific to this species. Although fMRI approaches using sedation and restraint have provided some insight, particularly regarding basic sensory processes in dogs (Willis et al, 2001;Bach et al 2013), chemical and physical restraint limit the types of neural processes that can be studied, and many researchers shy away from using these approaches in dogs due to ethical concerns.…”

Functional Magnetic Resonance Imaging of the Domestic Dog: Research, Methodology, and Conceptual Issues

“…In order to optimize the amount of auditory stimuli that can be heard and processed, a sparse temporal sampling (STS) procedure may be used, as in Bach et al (2013) and Andics et al (2014). This sort of imaging paradigm allows for periods of scanner silence during which the auditory stimuli of interest may be presented without interference.…”

“…Because the BOLD response lags in time behind the neural response, acquiring imaging data shortly after, but not during, auditory stimulus presentation allows capture of the stimulus-evoked hemodynamic response function. Bach and colleagues (2013) implemented this procedure and compared it with a standard scanning procedure without intermittent silent periods. Though the dogs were anesthetized and some degree of signal attenuation could be expected, the authors found reliable activation of auditory areas for all of the dogs.…”

“…Such concern is evidenced by brain structure analyses conducted by Roberts et al (2010), in which it was found that brachycephalic dogs possess skulls with comparatively rotated cerebral hemispheres, pitched brain angle at the anterior pole, and repositioning of the olfactory lobe. To combat the exclusivity of normalized images due to such differences, Bach et al (2013) suggest a wider scope of canine structural imaging to include a variety of skull shapes. Along those lines, they suggest the development of a database similar to what is seen in BrainMap for human data (Laird, Lancaster, & Fox, 2005), where imaging data from a multitude of canine fMRI studies may be accumulated, analyzed, and normalized.…”

“…Such studies have provided knowledge of canine neural responsiveness, cognitive effects of aging, neuroimaging efficacy, and health viability, and thus we first discuss the work done with anesthetized dogs in this paragraph. Bach et al (2013) used fMRI to successfully identify neural regions associated with processing of auditory stimuli, as well as establish the efficacy of fMRI with anesthetized dogs in regard to auditory stimulus presentation. Su et al (2005) used longitudinal structural MRI to investigate the time course of neural correlates of canine cognitive decline (e.g., ventricular enlargement, lesions), strengthening the potentiality of the dog as a model of human aging.…”