Myth-busting: Do horses have a frontal lobe / PFC?

TL;DR: Do horses have a frontal lobe or PFC? Yes.

For the rest of you who want to know more…

Biology basics

Dr. Steve Peters and I often get the question from our Equuscience students about whether or not horses have a frontal lobe or a frontal cortex / pre-frontal cortex (PFC), which is an area of the brain involved in executive functioning (thinking, reasoning, planning, attention, working memory), emotion regulation, language and communication, social cognition, and voluntary movement.

The belief that horses lack a frontal lobe or PFC (which is a subsection of the frontal lobe) is widespread in the equine community, while others insist that horses do have one, which leads to confusion.

This post is an amalgamation of thoughts and information that Steve and I have shared in our group, along with additional legwork to locate relevant sources, in an effort to make this information more widely available.

Image from Matiasek et al. (2007)

All mammals have a frontal lobe

The first thing to understand is that all mammals have a frontal lobe / PFC.

Vernier (2018) states: “Although present in all the mammalian species known so far, the frontal lobe, and especially its prefrontal domain, is one of the most variable brain regions among mammalian species, even among individuals. The prefrontal cortex (PFC) exhibits a lot of variations not only in size (from 35% of the total brain volume in humans to less than 4% in the cat for example)“.

Kolb (2010) provides an overview of the different criteria that are involved in determining that all mammals (with the exception of cetaceans; see below) have a prefrontal cortex / frontal lobe or similar structure, though there are differences across species in terms of functionality and the geographic boundaries of the PFC are are complicated to determine with complete certainty.

Horses are mammals

This does not require explanation 🙂

Ergo, horses have a frontal lobe

Straightforward, right?

However, let’s continue to dig a bit further. What does the literature have to say?

Literature review

Equine neuroanatomy through dissection or imaging:

Clark (1893) in an article about pigs briefly discusses the frontal lobe of horses.

MacCallum and Buckley (1901) conducted post-mortem dissections on the brains of 4 horses that died of leucoencephalitis. The authors describe the frontal lobe.

Marchand and Petit (1911) described a glioblastoma / sarcoma in the frontal lobe of a horse (as cited in a literature review by Jungherr and Wolf, 1939).

von Monakow (1914) measured the frontal lobes of horses, cattle, and goats, and determined them to be about 25% of the brain’s total volume in these species (as cited in Kasak, 1921).

Kellerman et al. (1990) conducted necropsies on two horses related to neurotoxicosis. The study identified the frontal lobe of one of the two horses, and includes a photograph of the anterior frontal lobe of the left cerebral hemisphere.

Plumlee and Tor (1997) conducted dissections on the brains of 10 horses, where the frontal lobe was identified along with the parietal lobe, temporal lobe, occipital lobe, and other areas.

Image from Schmidt, Knemeyer and Heinsen (2019).

Frees et al. (2001) performed a necropsy on a horse that had been experiencing severe neurologic effects in response to an injection of formalin. The frontal lobe was visible during the necropsy and referred to a number of times in the article.

Ferrell et al. (2002) conducted MRIs on 12 horses with neurologic disease, and identified lesions in the frontal lobes.

Matiasek et al. (2007) provided a case report and MRI of gelding with neuroendocrine tumours. The frontal lobe is identified in this report, and it is identified in one of the images (which is included above).

Rodrigues et al. (2009) conducted necropsies on 9 horses that had neurologic disease, and the frontal lobes were identified as part of the routine process of histological examination.

Schmidt et al. (2019) conducted high-field 3Tesla MRI mapping of equine neuroanatomy. The article includes images of a horse brain, and the frontal lobe is named and is also visible (see image insert to the right).

This is but a small sample of studies, but it demonstrates that veterinary science and equine neuroscience have been aware of the frontal lobe of horses for some time, for at least 130 years.

Additional information to consider:

While none of the following articles is a confirmed slam-dunk, they nonetheless provide additional information that adds nuance to the picture.

Manger (2006) provides an in-depth overview of brain structure in cetaceans (dolphins, whales, and porpoises), which is the rare category among mammals that features minimal to no frontal lobe / PFC. Sea lions also have minimal PFC. Images are provided showing what brains look like that have minimal to no such brain region. Additional imaging related to dolphin brains can be located in Marino et al. (2002) and Hof et al. (2005), the latter of which suggests that the perception that cetaceans lack a frontal lobe entirely is misleading and that the question is more complex.

Roberts et al. (2016) discuss neural involvement in equine temperament, including the role of dopamine in reducing the PFC’s ability to regulate the amygdala as an proposed explanation for horses that have more anxious or nervous temperaments.

Kabadayi et al. (2018) review the literature on the detour paradigm, where animals of various species are presented with a situation where they must find a detour around a barrier to a destination. Their article discusses many of the contributing variables that explain variations in performance in finding detours, one of which is the PFC and its role in problem solving. Two studies have been conducted on the detour task in equines.

McBride et al. (2022) take a comparative psychology and neuroanatomy approach to impulsivity and compulsive behaviour in horses, in terms of similarities and differences with addictions and other impulsive/compulsive behaviour in humans. They reference animal model research on the PFC and its involvement in impulsive and compulsive behaviour, and discuss which circuitry may overlap and which mechanisms may be different between equines and humans.

Why has this myth gained traction?

If all mammals have a frontal lobe / PFC, how is it possible to have come to the conclusion that horses, of all land-based mammals, don’t have one?

It is possible that this belief emerged and has shown staying power due to six potential variables:

  • 1) A misunderstanding that since horses cannot reason in the same way as humans that this means they lack the area of the brain involved in reasoning (the frontal cortex/lobe). This is anthropocentric, making humans the yardstick by which to compare other species (as opposed to looking at the various abilities other species have that humans don’t have). It also works off the faulty assumption that a lack of a certain ability in horses means a lack of the corresponding brain area that explains that ability in humans. Rather, it is important to understand that the same structure may have some similarities as well as some differences in functioning, expression, and experience across species. This misunderstanding may also reflect human exceptionalism, which is when humans, as a species, tend to place themselves in a category by themselves when in fact other species also show evidence of similar traits, responses, or have comparable (neuro)anatomy. While humans are indeed different in some respects, this line of thinking avoids the ways that mammals are similar. Not acknowledging what is legitimately mammaliomorphic (of mammalian form; Schlote, 2017) in an attempt at not anthropomorphizing is actually anthropocentric.
  • 2) Diagnostic overshadowing, where something is deemed to be normal for a particular species (“this is just how they are”) when in reality the issue is evidence of something else altogether. In this case, many horses are exposed to chronic stressors in captivity that they would not experience ethologically in the wild, as a result of domestication. Traditional training methods are based on inducing appeasement, survival or shutdown states in horses, which may lead to the myth that horses are “flight animals”. Many horses are kept stalled, have limited turnout and opportunities for socialization and the expression of choice with regards to natural behaviours. When a nervous system is experiencing elevated stress, fight or flight activation, or shutdown, executive functioning and emotional regulation are affected. Research by Dr. Bruce Perry found that functional IQ can drop anywhere from 40 to 60 points depending on the nervous system’s state and how dangerous or threatening the conditions are. So there is a possibility that people falsely assume horses lack a frontal lobe because the horses they see in captivity aren’t showing evidence of “intelligence”, executive functioning, or emotion regulation, whereas in fact these horses may simply be dominated by nervous system states that reflect stress, fear, or terror. The issue would therefore not be a lack of frontal lobe (“this is just how horses are”), but rather the conditions at hand affecting the nervous system’s state and behaviour.
  • 3) A well-intentioned desire to not anthropomorphize equines by projecting onto them traits that are human, in order to ensure that we understand them in a way that is appropriate to their species. Therefore, claiming the horses lack a frontal lobe may be done in an attempt at helping people understand the differences between humans and horses, so as to not hold them to the same expectations as humans. However, similar to factor #1, it is essential to recognize that functionality of a particular part of anatomy may vary depending on the species; differences between species can still be honoured while recognizing that they may have the same or similar (neuro)anatomy.
  • 4) Cognitive distortion. Similar to point #1, because humans do have some traits and behaviours that are unique, and because some of what makes us uniquely human is due to the frontal lobe, it is simple to assume that horses do not have one. However, this may reflect the cognitive distortion of black and white or all or nothing thinking. For instance, while all mammals have a frontal lobe / frontal cortex (a sub-region of the brain), only primates have a ventrolateral frontal lobe (a sub-region within that sub-region), which can be further divided into 12 areas. Monkeys share 11 of these areas with humans, but only humans have a lateral frontal pole (a sub-region within a sub-region within a sub-region). Rather than name that horses do not have a ventrolateral frontal lobe or a lateral frontal pole, we throw out the baby with the bathwater, over-generalize, and claim they don’t have a frontal lobe at all.
  • 5) Human error. Some sources point out that horses have minimal frontal tissue or an undeveloped frontal lobe, which may be misinterpreted, misquoted, or misremembered as having no frontal tissue at all.
  • 6) Inaccessibility of the information. Even if factor #5 occurred, it is unclear where the interpretation that horses have minimal frontal tissue came from in the first place. von Monakow (1914) measured horse brains and found the frontal lobe to make up 25% of the volume of its brain (though the delineations confirming how the region was identified are not known). Semendeferi et al. (1996) confirm that the frontal lobe in humans makes up approximately 36% of the total volume by comparison with the cat where it makes up only 4% of the total volume (Vernier, 2018). If von Monakow’s calculation is correct, then a horse’s frontal lobe is not that minimal proportionately-speaking; the cat’s frontal lobe would be more deserving of that descriptor. Of course, von Monakow’s research is not well-known, having been published in German over a century ago, in a source that cannot be easily located. It took a few hours of diligent sifting through obscure references to track it down. Other more recent articles are somewhat easier to find, but this requires skill in locating research articles that have been published in peer reviewed journals and other academic sources, not all of which are available online for free (many are locked behind a paywall). The average individual may not know how to track down this information, or have the patience or desire to do so. It’s time consuming and not particularly practical.

There are many good reasons as to why this belief has shown such staying power. As research becomes more sophisticated, additional nuances will undoubtedly become clearer, requiring revisions to this article. For now, what is more practical is focusing on the differences in functional capacity of equine brains and being curious about what you can do to support and develop their capacities as effectively as possible, based on what is reasonable to expect for their species… a story for another time.

Thanks to Steve Peters for the Schmidt et al. (2019) source with the recent MRI and for helping me obtain the PDF of the 1939 article that allowed me to locate the Marchand and Petit (1911) French research citation which, similar to von Monakow’s 1914 German citation, has largely been lost due to the passage of time.

For more information about Equuscience courses, visit our website. Our master class (7 modules jam packed with interesting information) starts on May 27, 2023, and there are still spots available.

Interested in seeing an equine frontal lobe in person? Steve also runs horse brain dissection workshops where participants have the opportunity to hold and explore equine neuroanatomy in a hands-on way. Plus, Steve and I are leading our inaugural Equuscience Retreat (an educational and wellness fusion event) at Apache Springs Ranch in Sonoita, Arizona from February 22-26, 2024 (registration not yet open, but some details are available at the link). There will also be an optional horse brain dissection at this event, followed by a burial ceremony near the labyrinth to honour the horses in question.

*This article was updated on May 29, 2023


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