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Lateralization in Horses
Hemispheric Lateralization in Horses
As an avid equestrian, I can’t help but be interested in the way that the brain of a horse works. I’ve constantly wondered why my horse Demetrius spooks when he sees another horse do so, or why I have to ride each exercise both to the right and to the left. When I discussed these questions with a friend who is also interested in horses, she mentioned to me that horse brains are lateralized similarly to human brains. A journal article explains lateralization, “…the essence of lateralization lies in the fact that one side of the brain performs certain types of computational operations and the other side performs other, different computational operations.”[1] This made a great deal of sense to me – lateralization contributes to handedness in humans, but horses are known to be somewhat handed as well. That is to say, when moving on a circle, it might be easier for a horse to move in the left direction than it is for him or her to move in the right. The same concept applies to humans in the form of right or left-handedness, or which hand is dominant on a given human. Consequently, I began to wonder if horses are lateralized due to their primal instincts as prey animals.
In the horse world, there are an exhausting number of theories regarding horsemanship and training. Clinton Anderson, a prominent Australian horse trainer, developed one of these theories. In his training manual, Anderson explains that “The horse’s brain has two sections: one is for thinking and the other controls reacting. The reacting part is big. The thinking part is very small.”[2] The notion that there are two parts of the horse’s brain is interesting in that it parallels the idea that there are two hemispheres in the brain, but I found it too simplistic. I was sure that there were more than two parts of the equine brain, and that that the reacting part and the thinking part actually had names. Anderson’s theory was a good starting place for my research, but I wanted to understand the scientific reasons for lateralization in horses.
In my childhood riding lessons, my trainers always told me to work the horse in both directions so that they built muscle on both sides. Every horse I rode had a side that was easier to work, just as many humans have a hand with which they prefer to write. In a journal article by Stefano Ghirlanda and Giorgio Vallortigara, the pair investigates possible reasons for hemispheric lateralization in prey animals. The article cites a study by McGrew and Marchant done in 1999 on chimpanzees in which “…individuals with a stronger hand preference forage more efficiently, but this does not depend on which hand is preferred.”[3] McGrew and Marchant’s study presents an interesting thought; did vertebrates develop lateralization for a purpose? If so, was it for the purpose of hunting and foraging as this study proposes? The authors put forth another idea, “We consider predators and group-living prey meeting in contests where prey have two lateralization strategies available: ‘left’ and ‘right’. We assume that, when a predator attacks, lateralization affects the probability of prey escape in two ways…prey lateralized in the same direction have a greater chance of keeping together as a group.”[4] Not only are horses animals of prey, but they’re also pack animals. So if horses evolved to be lateralized, and the tendency is for them to be left-handed, they should be able to cope with predation pretty well according to the theory. This is another potential reason for the development of lateralization in animals of prey.
An idea that distinguishes between predator lateralization and prey lateralization is eye placement. Evolutionary theories have suggested that frontal eye placement was a development that only occurred in predators, while lateral eye placement was commonplace in prey animals. G. Vallortigara, L.J. Rogers, and A. Bisazza speculate, “Perceptual asymmetries, in particular, seem to be ubiquitous in everyday behaviour of most species of animals with laterally placed eyes…adjustment of head position and eye movements may play a similar role in mammals with frontal vision as does the choice for right or left lateral visual fields in animals with laterally placed eyes.”[5] The concept that the movement of the head and eyes is a similar function to coordinating the left and right visual fields is interesting in that it differentiates between the lateralization of a predator and an animal of prey.
While we can’t make a definite conclusion as to the evolutionary reasons for lateralization in horses and other prey animals, each of the theories provides insight into the question. Speculating on the potential reasons for lateralization can also shed light on the behavioral patterns of horses, helping humans to work with them in more effective ways. On a personal level, understanding Demetrius’ primal reactions to the world around him gives me a sense of empathy with him; I deeply appreciate the work he does with me, and how his brain works in doing so.
References
Anderson, Clinton Anderson’s Downunder Horsemanship: Establishing Respect and Control for English and Western Riders (North Pomfret, Vermont: Trafalgar Square Books, 2004), 1.
Bisazza, A., Rogers, L.J., and Vallortigara, G., “Possible evolutionary origins of cognitive brain lateralization,” Science Direct (1999): 4.http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6SYS-3XMGP43-4&_user=400777&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1025349589&_rerunOrigin=scholar.google&_acct=C000018819&_version=1&_urlVersion=0&_userid=400777&md5=71e783360728589d2787f70ba397e9b8
Ghirlanda, Stefano, and Vallortigara, Giorgio, “ The evolution of brain lateralization: a game theoretical analysis of population structure,” The Royal Society (2004): 2,
http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1691668&blobtype=pdf
[1] Bisazza, A., Rogers, L.J., and Vallortigara, G., “Possible evolutionary origins of cognitive brain lateralization,” Science Direct (1999): 4. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6SYS-3XMGP43-4&_user=400777&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1025349589&_rerunOrigin=scholar.google&_acct=C000018819&_version=1&_urlVersion=0&_userid=400777&md5=71e783360728589d2787f70ba397e9b8
[2] Anderson, Clinton Anderson’s Downunder Horsemanship: Establishing Respect and Control for English and Western Riders (North Pomfret, Vermont: Trafalgar Square Books, 2004), 1.
[3] Ghirlanda, Stefano, and Vallortigara, Giorgio, “ The evolution of brain lateralization: a game theoretical analysis of population structure,” The Royal Society (2004): 2,
http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1691668&blobtype=pdf
[4] Ghirlanda, Stefano, and Vallortigara, Giorgio, “ The evolution of brain lateralization: a game theoretical analysis of population structure,” 2.
[5] Bisazza, A., Rogers, L.J., and Vallortigara, G., “Possible evolutionary origins of cognitive brain lateralization,” 1.
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| This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated. |
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Update
I did end up doing some research on this topic. Here is a link to a presentation I did for the Animal Behavior Society: www.youtube.com/watch?v=Wlcz6y42eUI
Effects of Laterization in Wild Horses
I do pre-adoption mustang gentling and get to work with horses who have never been handled prior to their entry to my training pens.
Some newly captured mustangs show a great deal of lateralization. Some will guard one side of their body and not let you on that side. Sometimes it is the right and sometimes it is the left, but it tends to stay consistent for the horse to a point, then it may suddenly flip (but I only saw it do that in one horse)
I am currently working with a young mare who only wants me on her right side and I am using the opportunity to explore this phenomenon. My best results have come when I give her food rewards for looking at me with her left eye. I am trying to classically condition the good feeling of eating a mouthful of hay with a view of me in her left eye. It seems to be helping, but it is slow going. She will let me rub that side of her face with a flag and let me put fly ointment around her eye by reaching over her face, but she is relucant to look at me with her left eye. Once I am in that field of vision, she doesn't mind me petting or brushing her on that side. It really has to do with the view of me, more than physical contact. She will guard that side for hours and would never let you over there if she had a choice.
The horses that come in with this type of predisposition are MUCH MUCH harder to train than balanced horses. You have to train the wild side 5 times more than the friendly side. And if you try to take the easy way out and stick to the friendly side, the wild side becomes even more inaccessible. Your best bet is to deal with that problem first because it is not going to just go away.
I am planning to do some studies of this to see how it relates to the organization of individuals in the herd. I get whole bands of horses in and they have two days before they start training, so I am planning to document their spatial arrangements and then when they are trained see if it relates to any lateralization problems. If anyone has an idea for a good experiment on this phenomenon, please contact me --
skittishness
This past summer, my horse has shown increased skittishness with objects, horses or other things aproaching on his right side, to the point he spins around and rears up a bit. It's been frightening, with a couple spills for me (luckily not hurt). He is 7 yrs old, and did not show this tendency last year. He had an episode last year where he'd been tied to a post and it came out and then chased him- very frightening to him I think. Then this spring, he tripped and had a fall. After that, the increased skittishness came. I love this horse and want to keep him, but I'm a bit afraid of having a serious injury while on him with the sometimes unpredictable spooking (I've always thought myself a good rider). I will not let an inexperienced rider on him for fear they'd get hurt. I'm working more and more on ground work with desensitizing him, and he's shown improvement; that doesn't seem to impact the trail rides much, esp if in open areas, and with some wind. What should I do?
Thanks!
As an equestrian rider I have also been finding how wonderful the brain works of the horse. I have been riding for serveral years and i just havent found the tim eto look all this up. This Website just gives it all! thanks soo much :)
this subject is very
this subject is very intristing. im doing my science project on horse brain laterzation.
forms of brain function in horses and humans
My guess is that "reacting" vs "thinking" is something different from "lateralization" ... in both horses and humans. And that some additional thinking about both can help us understand better both horses and humans, as well as the interactions between them.
horse brain lateralization
Hi Paul -
Just wondering if you've found or done any research that explored this issue in greater depth. I'm a psychotherapist (for humans) and was curious about certain commonalities between people and horses with regard to emotional processing.
All the best,
Abba Cohen