A standardized brain atlas has been created by US researchers using a powerful 3-tesla MRI machine. They say the atlas will be a fundamental resource for neuroimaging research.
It has been made freely available as an online resource for other researchers to use.
Philippa Johnson and her colleagues at Cornell University observed that brain atlases had, until now, been created for many species, but not for horses.
The researchers, writing in the journal Frontiers in Neuroanatomy, noted growing interest in the horse for behavioral, neuroanatomic and neuroscientific research due to its large and complex brain, cognitive abilities and long lifespan.
The adult horse brain weighs on average 606.07 grams and has a highly convoluted and complex pattern of sulci and gyri (grooves and folds). The gyrification index for the horse is one of the highest in domesticated animals.
“The large and complex nature of the horse brain provides distinct neuroanatomical similarities to humans, that rodent models may lack,” they said.
“In addition, the horse exhibits testable cognitive function, being able to the perform learning, discrimination, match-to-sample and memory tasks commonly used in neurological testing, and automated systems have been developed to test equine cognitive function.”
Collectively, this made the horse neurologically interesting and a potential large animal model for several neuropsychological diseases.
To create the atlas, the study team took MRI images of the brains of nine horses, still in their cranium, which had been euthanized for reasons unrelated to the study.
The atlas was generated using linear and non-linear registration methods and quality-assessed using signal and contrast to noise calculations.
Tissue segmentation maps for white matter, gray matter and cerebrospinal fluid were generated.
The end result is a high-resolution anatomically correlated three-dimensional population-average brain atlas for the species.
All subjects had higher whole brain, grey matter and white matter volumes on the right side, consistent with the well documented right forebrain dominance of horses, the researchers found.
They also found that whole brain and grey matter volume trended down with increasing age of the horse, whereas white matter volume trended up.
However a statistically significant correlation between age and tissue volume was not identified.
Discussing their work, the researchers said the atlas used nine subjects, which is similar to that of other brain atlases. However, given the limited numbers, this could result in some bias from the true average.
“Additionally, our cohort had more geldings than mares and included no stallions. This limited our ability to test the effect of sex and neutered status on brain tissue volume.”
Sex-related differences have been observed in human grey matter and white matter, but significant differences were not identified in an evaluation of sheep brains. “So the true impact of this limitation on the resultant brain atlas remains unclear.”
The atlas will provide an important tool for automated processing in equine and translational neuroimaging research, the researchers say.
The full research team comprised Johnson, Valentin Janvier, Wen-Ming Luh, Marnie FitzMaurice, Teresa Southard and Erica Barry, all with Cornell University in Ithaca, New York.
Equine Stereotaxtic Population Average Brain Atlas With Neuroanatomic Correlation
Philippa J. Johnson, Valentin Janvier, Wen-Ming Luh, Marnie FitzMaurice, Teresa Southard and Erica F. Barry.
Front. Neuroanat., 03 October 2019 | https://doi.org/10.3389/fnana.2019.00089