Of horses and humans, spiders, fears, and phobias
08/19/2024
Fear responses in horses can be incredibly unsettling. On some days, it feels like there's a saber-toothed tiger lurking behind every corner, a shark hiding in every puddle, and the typically mundane riding arena suddenly transforms into an ancient Roman coliseum filled with gladiators and predators—all because someone left an unfamiliar object in the corner. While factors such as breed, experience, welfare, and health issues all contribute to a horse's reactivity, let's be honest: despite our understanding and empathy for these flight animals, we've all had moments where we thought, 'Really? Come on!'"
I'm the first to argue that mammals have more in common than what sets us apart. However, it's crucial to consider the specific habitat and lifestyle of the species in question, as these factors determine which behaviors are most adaptive. Naturally, the principle that physiology and morphology follow function explains the significant differences in how we mammals utilize our shared physiology (you can read more about this in my blog post: Of Horses and Humans, Science, and Anthropomorphism). Even so, I must acknowledge the major differences between horses, as flight animals, and humans, as social hunters. Our lifestyles are fundamentally different, and as a result, not only do we differ in appearance, but our physiology and neurophysiology also reflect these distinctions.
Aside from morphology—such as the horse having the largest eyes of any land mammal, highly specialized for detecting predators—the most significant difference between humans and horses is likely the 'fight-or-flight' response, the active stress reaction. As flight animals, horses are finely tuned to detect predators as quickly as possible and then immediately “hit the road”. Their evolutionary advantage lies in their speed. Over time, horses have become specialized as the fastest runners, preferring to flee one time too many rather than miss a predator even once. Any horse that made this mistake has most likely not contributed to the future genetic pool of its species.
Humans, as social hunters, have taken a different evolutionary path. We've learned to control our fear. Imagine a group of humans hunting a mammoth—a large and dangerous animal. Successfully taking down such a creature requires strategy, coordination within the group, and, most importantly, the ability to maintain a clear mind. Panic and fear would only lead to chaos, leaving others in danger. It's likely that this role as social hunters led to the development of an over-proportionally large brain structure in primates, known as the prefrontal cortex. This region is most prominent in humans and is essential for planning, strategizing, and, crucially, controlling fear.
While there is good scientific evidence that horses do possess a prefrontal cortex (see my blog: Thinking, reasoning, and the equine brain: Do horses have a «prefrontal cortex”? Let’s think about it! ), it’s also clear that they tend to bypass or not engage this part of the brain in threatening situations. For a flight animal, the ability to plan, strategize, or control fear in an emergency isn't necessary—so, naturally, horses don’t rely on these functions when faced with danger.
Dear reader, you might be wondering, where am I going with this? Just a moment, I’m getting there 😉. Evolution has a curious trait: it never forgets. Once a structure or trait is established, it remains. It can be modified, adjusted, given an 'add-on' that changes its purpose, or even overridden—but it can’t simply be discarded. This principle can sometimes result in the persistence of older evolutionary reactions, even if they are no longer functional. Phobias in humans likely represent one such evolutionary relic that may resurface under certain conditions.
Spider phobia is a great example of an evolutionary old fear reaction that, in our modern world, has become dysfunctional. Those who suffer from spider phobia are fully aware that spiders are usually harmless, yet they still experience an uncontrollable fear and panic reaction at the sight of one. Generally, people with spider phobia are perfectly 'normal'—they're not overly anxious, not depressed, just as normal as can be, except for that 'little' uncontrollable fear of spiders, which can make life difficult.
Now, I’d like to suggest that this uncontrollable, irrational fear is an ancient evolutionary response, akin to the 'normal' fear reaction of our four-legged companions—except that their fear response is much more powerful! While humans have spent millions of years developing a neural mechanism to control fear, horses have spent the same amount of time perfecting their fear response, particularly their fight-or-flight reaction.
Let's take a closer look at spider phobia. If you dare, you can even take a closer look at a spider here 😉.
I'm not someone with a spider phobia, but I have to admit that, while I find spiders fascinating and appreciate their role in nature, I don't particularly enjoy looking at them. And in this, I’m probably not much different from many of us.
In principle, humans can develop irrational fears of almost anything, often stemming from a learning history or a traumatic experience. However, certain stimuli—such as spiders, snakes, and heights—tend to trigger fears more easily, even when there’s no clear traumatic event to explain the development of a phobia. In a way, we are predisposed, or 'prepared,' to develop fears in response to these particular stimuli. Conversely, we are much less likely to develop a phobia of objects like irons, washing machines, or flowers. But why is that?
As early as 1971, psychologist and emotion researcher Martin Seligman proposed the Preparedness Theory, which posits that each species is predisposed to certain phobic fears (republished in 2016). For humans, it appears that spiders, snakes, and heights hold a special biological significance. These fears are so deeply ingrained that even individuals who have never visually encountered a spider, such as those who are blind, may still experience arachnophobia (Musial et al., 2009).
Let's examine what occurs in the brain of someone with a spider phobia. To fully understand a phobic reaction, it's helpful to first explore how a non-phobic reaction manifests. For example, Figure 2 illustrates the brain activity of an equestrian when viewing a nice little horse:
In this example, sensory information, which is visual, travels to a structure known as the "Thalamus." With the exception of olfaction (the sense of smell), all sensory information from the periphery reaches this structure and is then relayed to other brain regions and neural networks. This is why the Thalamus is often referred to as "the gateway to consciousness." From the Thalamus, the sensory information proceeds to the Cortex, where it is assessed and a potential response is planned. If the stimulus is evaluated as potentially dangerous, the Amygdala—a central brain structure involved in the emotions of fear and aggression—activates the fight-flight response. The Amygdala coordinates the hormonal (stress hormones), autonomic (blood pressure, heart rate, metabolism, etc.), and behavioral responses (such as running or fighting) associated with this reaction. Simultaneously, a copy of the incoming sensory information is sent directly from the Thalamus to the Amygdala. This direct pathway is phylogenetically ancient and is usually overridden by the cortical pathway in humans. For those interested in a more detailed exploration of the brain mechanisms of fear, I recommend reading the works of LeDoux (1989 and 2016).
So, what happens when a human sees a non-threatening stimulus? In case of an equestrian spotting a cute horse (Figure 2), a positive emotional rection is triggered (“so cute”) and maybe a motor reaction as well, but this will most likely be directed towards the horse and not away from him 😉
Let’s see what happens in case of e fear reaction. Figure 3 illustrates the brain's response when a human spots a predator, in this case, a saber-toothed tiger.
Figure 2: Simplified (very 😉) schematic of the processing of a non-threatening stimulus in the human brain (based on and adjusted according to Birbaumer & Schmidt: Biologische Psychologie. Springer, Berlin, 1996).
Figure 3: Simplified (very 😉) schematic of the processing of a threatening stimulus in the human brain. The information from the sensory organs is transferred through the Thalamus to the Cortex and evaluated. The Cortex signals “danger” to the Amygdala and a fear reaction is triggered (based on and adjusted according to Birbaumer & Schmidt: Biologische Psychologie. Springer, Berlin, 1996).
When sensory information about a predator is detected, it is transmitted through the Thalamus to the Cortex for evaluation, while simultaneously, a copy of this information is sent directly to the Amygdala. The Cortex identifies the signal as "danger," prompting the Amygdala to trigger a fight-flight reaction. Thus, sensory information is processed mostly consciously in the Cortex, albeit at maximum speed.
Primates, particularly humans, have a significantly large pre-frontal portion of the Cortex, which is crucial for controlling fear and exerting inhibitory control over motor reactions. This unique capability allows humans to decide not to flee upon spotting a predator. Remarkably, humans, as social hunters, have evolved their brains to control fear—a trait that appears to be quite unique in the animal kingdom. After all, fear serves a protective function; it is a mechanism that helps ensure survival.
The brains of individuals with spider phobia exhibit several fascinating capabilities. For instance, they can identify a spider much faster than anyone else, even amidst confusing arrays of flowers (if you ever need to catch a spider for a study on arachnophobia, consider bringing someone with this phobia to the park—they are exceptionally skilled at spotting spiders!). This extraordinary ability and focus on spiders, a phenomenon known as hypervigilance, is supported by heightened electrophysiological activity in the brain, (e.g., Kolassa et al., 2007).
Additionally, when examining heart rate and other biological indicators of stress, it becomes evident that the stress response in spider phobics, when shown pictures of spiders, is so immediate that the image has not yet reached the cortex. This means the spider is not yet consciously perceived. Therefore, spider phobics can detect spiders in milliseconds, and their fear reaction is triggered BEFORE they are even consciously aware that they have seen a spider. This phenomenon is referred to as "subliminal" perception, which occurs below the limits of conscious awareness.
The extraordinary speed of the fear reaction, which occurs on a subconscious level, makes it challenging to control, because the stress response is already triggered and escalating before the cortex is even aware of the stimulus (in this case, the spider). This presents a significant challenge since the reaction can only be controlled by the (prefrontal) Cortex, which in this scenario is bypassed. Figure 4 illustrates the well-supported hypotheses about what happens in the brains of individuals with spider phobia when they encounter a spider:
A superfast, immediate flight reaction to even the slightest hint of a potentially dangerous stimulus operates on the principle of "run first—think later." Does that sound familiar?
Humans, as social hunters, have evolved their brains—particularly the prefrontal cortex—to control fear with near perfection. This is quite the opposite of our four-legged friends, the horses. As flight animals, horses have needed to develop their fear response and flight reaction to absolute perfection. While both species share commonalities as social animals, our evolutionary paths in terms of self-defense, survival, and managing fear have taken fundamentally different directions.
While humans have become adept at controlling fear and basically bypass the Amygdala, horses are exemplary fear responders. They possess a much larger Thalamus and Amygdala compared to humans (Johnson et al., 2019), and their sensory and motor systems are highly specialized to detect potential threats (predators) and initiate a rapid flight response. Horses also have the largest eyes of all land-living mammals, providing them with an almost panoramic view due to the placement of their eyes on the sides of their heads. Additionally, they have exceptional hearing capabilities in all directions, and their olfactory system is nearly as developed as that of dogs, allowing them to even detect the direction of scents.
Therefore, as flight animals, horses possess an extensive and highly developed sensory apparatus, which is advantageous when scanning for predators in open steppes. The horse’s “alarm system” is engineered to operate at "maximum warp speed." Compared to humans, they utilize a "shortcut" from the senses directly to the fight-flight center in the brain, the Amygdala. Every aspect of the horse’s brain is finely tuned to ensure the fastest possible flight response.
Figure 4: Simplified (very 😉) schematic of the processing of a spider (threatening stimulus) in the brain of a spider phobic. The information from the sensory organs is transferred through the Thalamus directly to the Amygdala, where a fight-flight response is triggered. The cortex, even though informed later, is not involved in the elicitation of the fight-flight response. In spider phobics, the evolutionary old direct pathway from the senses, via the Thalamus to the Amygdala, which is normally inhibited has become active (based on and adjusted according to Birbaumer & Schmidt: Biologische Psychologie. Springer, Berlin, 1996).
To us humans, the fear reactions of our four-legged companions often seem completely "irrational." Indeed, that is precisely its purpose—to act without thinking! For a flight animal like a horse, this instinctive response is a fundamental aspect of survival. Nonetheless, this trait is probably one of the most challenging for humans to understand. Perhaps this is why dogs, which are descended from wolves, are much easier for us to relate to. Both humans and wolves are social hunters who have, over many millennia, hunted together. This co-evolution of two species with similar "lifestyles" has left a significant mark on our mutual understanding and behaviors.
It is indeed a marvel of mammalian brain evolution that no structure ever truly "disappears." Once a structure has been "invented", evolution cannot not discard it. However, evolution is an incredibly creative force, capable of adjusting, modifying, advancing, or controlling existing structures through the development of innovative brain regions (such as the control of the Amygdala by the prefrontal Cortex in the human brain).
Sometimes, in special circumstances, these evolutionarily ancient mechanisms may unexpectedly resurface, as in spider phobia and other anxiety and stress disorders. This phenomenon highlights the deep-rooted and enduring nature of evolutionary old mechanisms, that have played crucial roles in the survival and adaptation of species throughout evolutionary history.
Indeed, as horse lovers, there's an intuitive understanding that horses are "smart." However, their apparent overwhelming fear responses, have led to many misconceptions about their mental capabilities. I personally believe that their intelligence is systematically underestimated due to their "irrational" behavior once a fear response is triggered.
To truly appreciate the nature of our equine companions, it's essential to understand their way of life and how they have survived, perfectly adapted, for millions of years. Recognizing that their fear responses are a survival mechanism rather than a sign of limited intelligence and cognitive control can help us better understand and appreciate the complexity of their behavior and cognitive abilities. This perspective shift is crucial for developing more empathetic and effective approaches to training, handling, and caring for horses.
Indeed, the next time you find yourself facing a day where the saber-toothed tiger seems to be lurking around every corner, the barn shark hides in every puddle, and the riding arena feels like a Roman coliseum, just keep calm and remember the spiders. 😉
References:
- Birbaumer & Schmidt: Biologische Psychologie. Springer, Berlin, 2010
- Johnson PJ, Janvier V, Luh W-M, FitzMaurice M, Southard T and Barry EF (2019) Equine Stereotaxtic Population Average Brain Atlas With Neuroanatomic Correlation. Front. Neuroanat. 13:89. doi: 10.3389/fnana.2019.00089
- Kolassa IT, Buchmann A, Lauche R, Kolassa S, Partchev I, Miltner WH, Musial F. Spider phobics more easily see a spider in morphed schematic pictures. Behav Brain Funct. 2007 Nov 19;3:59. doi: 10.1186/1744-9081-3-59. PMID: 18021433; PMCID: PMC2216031.
- LeDoux J. Anxious: Using the Brain to Understand and Treat Fear and Anxiety Paperback – Illustrated, August 23, 2016. Penguin Books
- LeDoux J. Fear and the brain: where have we been, and where are we going? Biol Psychiatry. 1998 Dec 15;44(12):1229-38. doi: 10.1016/s0006-3223(98)00282-0. PMID: 9861466.
- LeDoux J. Synaptic Self: How Our Brains Become Who We Are Paperback – January 28, 2003. Penguin Books
- Musial F, Kolassa IT, Sülzenbrück S, Miltner WH. A case of spider phobia in a congenitally blind person. Psychiatry Res. 2007 Sep 30;153(1):97-101. doi: 10.1016/j.psychres.2006.12.017. Epub 2007 Jun 27. PMID: 17597227.
- Seligman ME. Phobias and Preparedness - Republished Article. Behav Ther. 2016 Sep;47(5):577-584. doi: 10.1016/j.beth.2016.08.006. PMID: 27816071.