It uses independent components analysis to identify spatially distinct, distributed networks of regions that covary across individuals, and computes their statistical relationship to other categorical or continuous variables. Alternatively, neuroanatomical variation may be explained primarily by body size rather than breed membership, with different breeds' brains representing minor, random, scaled-up or scaled-down variants of a basic species-wide pattern. Colored regions are all p < 0.05 after multiple-comparisons correction; t-statistic values are illustrated. However, it is important to remember that primates and carnivores diverged further back in time than primates and rodents: humans are more closely related to mice than to dogs. To carry out quantitative assessments of regional variation in gray matter morphology, we used the Jacobian determinants of the native-space-to-template spatial deformation fields to produce a variation intensity map. This procedure identified six components, each of which were thresholded at Z scores >1.96 or below 1.96. Moreover, we found that these networks differed across breed groups. If variation in dog brain anatomy is unrelated to behavior, then variation should be randomly distributed across regions. 2A). The wine we drink and machines that can think, Shades of Blue Stop a Mosquito Biting You. In the case of circuitry that is highly conserved across species, such as circuitry for reward and motivation or fear and anxiety, it is a safe bet that research on other species is a good indicator of the functional role of these systems in dogs. Importantly, a phylogenetic analysis revealed that most change has occurred in the terminal branches of the dog phylogenetic tree, indicating strong, recent selection in individual breeds. To provide a common spatial reference for measuring this variation, we created an unbiased, diffeomorphic template using the ANTS software package (Avants et al., 2009). 1-2. Finally, the cropped transverse and sagittal images were then rescaled so that the robust mean intensity of both images was 100, the images were averaged together, and then the brain mask applied to this combined image. Variation in these networks is not simply the result of variation in total brain size, total body size, or skull shape. Marghi Merzenich is the VP of Content for Posit Science. We also investigated the relationship between these covarying morphological components and the phylogenetic tree. We also found that selection for smaller body size has significantly influenced the internal morphology of the cranial cavity. Person to person, the human brain varies a little in size and shapebut not dramatically so. We produced a study-specific template representing the average brain morphology across the entire group, equally unbiased toward any particular image. As the brain has developed through evolution, the most recent addition has been the frontal lobe. This was accomplished using FSL's randomize, a tool for Monte Carlo permutation testing on general linear models (Winkler et al., 2014). Together, these results establish that brain anatomy varies significantly in dogs, likely due to human-applied selection for behavior. Broadway et al., 2017). In other words, the input to SBM consisted of gray matter maps for each subject, where intensity at each voxel corresponded to the degree of deformation required to come into alignment with the template (i.e., the demeaned log Jacobians). Size helps, but it isn't everything. Code is available online at. Images were opportunistically collected at the Veterinary Teaching Hospital at the University of Georgia at Athens from dogs that were referred for neurological examination but were not found to have any neuroanatomical abnormalities. Relationship between morphologically covarying regional brain networks and phylogenetic tree. This approach has become a standard approach in comparative biology to model trait change across a phylogeny. C, Brain-wide morphological variation, regardless of breed, as indexed by the SD of all dogs' Jacobian determinant images. Importantly, this grade difference in the neurocephalic to cephalic index aligns with a significant difference in body size (pANOVA: F = 9.73, p < 0.01; average body size 11 kg vs 23 kg in other breeds). This observation was further confirmed by a whole-brain, multiple-comparison-corrected, voxelwise statistical analysis (Fig. T2-weighted MRI images were acquired on a 3.0 T GE Healthcare HDx MRI unit with a GE Healthcare 51471372 3.0T HD T/R Quad Extremity Coil. D, A Monte Carlo permutation test on demeaned gray matter Jacobian determinant images revealed that much of gray matter shows significant deviation from group-mean morphology. Images are public-domain photos from Wikimedia Commons. These findings have relevance to both basic and applied science. Try Musicnot Junk Food, Your Brain in Love: Part 4 Oxytocin, the Love/Hate Hormone, Your Brain in Love: Part 3 The Neuroscience of Date Night, Your Brain in Love: Part 2 Love and Marriage, https://www.youtube.com/watch?v=eMlg5os1OLM. 4). Daniel - While it appears that differences in brain size could make larger dogs more skilled in some areas, its not fair to say that they are massively more intelligent than their smaller counterparts. The precruciate and prorean gyri house premotor and prefrontal cortex, respectively, while the gyrus rectus is part of medial prefrontal cortex. This might be akin to studying language circuitry in a lineage of language-deprived humans: humans almost certainly have some specialized hard-wired adaptations to this circuitry, but experience is required for the anatomical phenotype to fully emerge, and indeed it is difficult to consider language-related neural adaptations divorced from the context of language exposure and learning. To identify regional covariation in gray matter morphology, we used GIFT, a software package for MATLAB (Calhoun et al., 2001). Results revealed six networks where regional volume covaried significantly across individuals. Finally, on a philosophical level, these results tell us something fundamental about our own place in the larger animal kingdom: we have been systematically shaping the brains of another species. Therefore, shifts in relative brain size may be related to expansion or contraction of specific networks, potentially leading to the presence or absence of correlations between body size and behavior depending on the specific breeds or behaviors being studied. Importantly, this revealed that a large proportion of the brain shows significant gray matter morphological variation across subjects, as illustrated in Figure 1D. During nonlinear registration, a warp-field is produced that represents the mapping from the original image to the target image. Sagittally acquired images ranged from 0.273 mm2 in-plane resolution and 3.200 mm slice distance to 0.430 mm2 in-plane resolution and 3.200 mm slice distance. There is substantial diversification of skull shape across dog breeds, and this has been linked to behavioral differences (Drake and Klingenberg, 2010; McGreevy et al., 2013). Neuroanatomical variation is plainly visible across breeds. This was accomplished using source-based morphometry to identify maximally independent networks that explain the variation present in the dataset. To our knowledge, the dogs in the current study were all house pets. Specific associations between associated brain networks and behavioral specializations are also apparent. DOI: https://doi.org/10.1523/JNEUROSCI.0303-19.2019, A new look at statistical nodel identification, Behavioral functions of the mesolimbic dopaminergic system: an affective neuroethological perspective, Voice-sensitive regions in the dog and human brain are revealed by comparative fMRI, ANTS: Advanced Open-Source Tools for Normalization And Neuroanatomy, Penn Image Computing and Science Laboratory, University of Pennsylvania, Does size really matter? This cannot be assumed to be the case for circuits that involve higher-order cortical association areas. A phylogenetic analysis revealed that changes in relative brain size are not predicated by relatedness and are more likely the result of selection on specific terminal branches of the phylogenetic tree (i.e., individual breeds). A, Brain volume versus body mass. Additional research is needed to definitively link the function of each network to its adaptive role in response to behavior selection. This suggests that brain evolution in domestic dog breeds follows a late burst model, with directional changes in brain organization being primarily lineage specific. Thus, future studies on purpose-bred dogs that are actively performing the tasks for which they are presumably adapted might expect to find additional or more pronounced neuroanatomical effects than we observed here. Significant breed differences in temperament, trainability, and social behavior are readily appreciable by the casual observer, and have also been documented quantitatively (Serpell and Hsu, 2005; Tonoike et al., 2015). Cephalic index is defined as the ratio of skull width to skull length 100. The only difference between standard and phylogenetic least-squares approaches is that the phylogenetic approaches weight data points according to phylogenetic relatedness (Rohlf, 2001). Tentatively, this network might be relevant for social bonding to humans, training, and skill learning. It might be possible, for example, to identify neural features that are linked to different breeds' specializations for specific behaviors, and to selectively breed or train dogs for enhanced expression of those neural features. Network 5 includes limbic regions that have a well established role in fear, stress, and anxiety, including the hypothalamus, amygdala, and hippocampus and adjacent dentate gyrus (for review, see Tovote et al., 2015). B, Neurocephalic index vesus cephalic index. These results indicate that through selective breeding, humans have significantly altered the brains of different lineages of domestic dogs in different ways. How much do we expect to get out of this energy wise for what we put in, is it twice as much out or 1000 times as much out? Associations between brain networks and related behavioral specializations are apparent. Next week its Steves question about fusion. Humans have selectively bred dogs for different, specialized abilitiesherding or protecting livestock, hunting by sight or smell, guarding property, or providing companionship. We therefore used phylogenetic comparative methods that account for phylogenetic nonindependence by including expected phylogenetic variance-covariance among species into the error term of generalized least-squares [phylogenetic generalized least squares (pGLS)] linear models (Rohlf, 2001). T2-weighted images underwent bias field correction using ANTS's Atropos N4 tool (Avants et al., 2011) and segmentation into gray matter, white matter, and CSF using FSL's FAST tool (Zhang et al., 2001). 2B). In addition to these analyses of the gross external shape and size of the brain and skull, we also investigated internal brain organization. First and foremost, our findings introduce neural variation in domestic dog breeds as a novel opportunity for studying the evolution of brainbehavior relationships. Additionally, a study that used a single scaling metric across breeds found that larger-brained (i.e., larger-bodied) dogs performed better on tests of executive function (Horschler et al., 2019). 1A). Circles indicate factor loading. Download, NiPype pipeline for merging axial and sagittal images from each dog before registration to the template. The preprocessing pipeline was implemented using the NiPype workflow engine (Gorgolewski et al., 2011). We observed the latter (Fig. These were entered into in a multiple regression analysis using the GIFT Source Based Morphometry toolbox. Mel Jans-Singh spoke to biological anthropologist Daniel Horshcler and neurologist Tim Rittman John - Dogs come in all sizes, from tiny Chihuahuas to giant Great Danes. Terms and Conditions | Privacy Policy | Security Policy | Sitemap. Figure 2B shows the relationship between neurocephalic and cephalic index. 1-1 and a detailed NiPype registration workflow is included in Fig. This means that some dogs can have a brain twice as big as other dogs.We put this question on the forum and twitter. These were grouped into 10 different breed groups as defined by American Kennel Club (AKC), which ostensibly represent groupings that were developed for similar behavioral specializations, such as herding or hunting. greyhound adoption memphis, Identify maximally independent networks that explain the variation present in the dataset in dogs, due... Means that some dogs can have a brain twice as big as other dogs.We put this on! To both basic and applied Science < 0.05 after multiple-comparisons correction ; t-statistic are. Multiple regression analysis using the NiPype workflow engine ( Gorgolewski et al., 2011 ) related behavioral specializations also... 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