Characterization of Structural Connectivity of the Default Mode Network in Dogs using Diffusion Tensor Imaging

Abstract

Diffusion tensor imaging (DTI) provides us an insight into the micro-architecture of white-matter tracts in the brain. This method has proved promising in understanding and investigating the neuronal tracts and structural connectivity between the brain regions in primates as well as rodents. The close evolutionary relationship between canines and humans may have spawned a unique bond in regard to social cognition rendering them useful as an animal model in translational research. In this study, we acquired diffusion data from anaesthetized dogs and created a DTI-based atlas for a canine model which could be used to investigate various white matter diseases. We illustrate the application of this atlas by calculating DTI tractography based structural connectivity between the anterior cingulate cortex (ACC) and posterior cingulate cortex (PCC) regions of the default mode network (DMN) in dogs. White matter connectivity was investigated to provide structural basis for the functional dissociation observed between the anterior and posterior parts of DMN. A comparison of the integrity of long range structural connections (such as in the DMN) between dogs and humans is likely to provide us with new perspectives on the neural basis of the evolution of cognitive functions.

Resting state networks of the canine brain under sevoflurane anaesthesia

“…Only one RSN, the DMN, does not match in both studies. While our results correspond to the results of Kyathanahally et al [16], that showed dissociated DMN in dogs in rs-fMRI as well as in DTI [53], this could not be reproduced by Szabó and colleagues [17]. [12,60].…”

“…Weaker connectivity between the anterior and posterior component in dogs has been supported using diffusion tensor tractography, which only identified white matter tracts connecting medial prefrontal cortex/anterior cingulate cortex to the posterior cingulate cortex in 9/23 dogs [53], while in humans these tracts were identified in 22/23 subjects [54]. This was also reflected by a significantly lower group fractional anisotropy in dogs in this area compared to humans [53]. Dissociation of the DMN has been found in children and in patients with Alzheimer's diseases and may reflect a lower level cognitive processing [52].…”

Stereotaxic Diffusion Tensor Imaging White Matter Atlas for the in vivo Domestic Feline Brain

“…While the DWI population template was upsampled to 0.5 mm 3 using advanced processing methods for structural connectome creation, these techniques use a significant amount of interpolation potentially biasing the data with artificial inflation. Higher-resolution DTI imaging has been achieved at higher field strengths or at the compromise of the number of diffusion directions (Zakszewski et al, 2014;Robinson et al, 2016;Hutchinson et al, 2017). In order to ensure that the lower resolution did not compromise the resulting tractography reconstructions, we validated our results by comparing our tract reconstructions to gross anatomic white matter dissections.…”

“…Despite the cat being a widespread preclinical animal model in neuroscientific research, this species lacks the open-source stereotaxic MRI-based brain atlases available in other species (Mori et al, 2008;Jiang and Johnson, 2011;Rumple et al, 2013;Zakszewski et al, 2014;Robinson et al, 2016). The only open-source stereotaxic feline MRI atlas currently available is created with structural T1-weighted MRI data and focuses on cortical and deep gray-matter structures (Stolzberg et al, 2017).…”

“…This produces a highly sensitive probability distribution of connections that can be thresholded to include only the most likely connections (Jones, 2008). Both these forms of tractography have been used to create functional white matter brain maps that are routinely used, in the human, rhesus macaque, rat, mouse, dog and ferret research (Mori et al, 2008;Jiang and Johnson, 2011;Rumple et al, 2013;Zakszewski et al, 2014;Calabrese et al, 2015;Robinson et al, 2016;Hutchinson et al, 2017). Tractography techniques have been used to document the anatomy of feline white matter tracts (Jacqmot et al, 2017) and evaluate the development and regional variation of white matter in the juvenile feline brain (Takahashi et al, 2009;Dai et al, 2016).…”