Potential Neural Consequences for Snakes Under Captive Management
Summary: Are snakes not thought to be intelligent because they’re really dumb, or are we making it impossible for them to reach their brainpower potential by forcing them to live in depressing, boring, stressful environments? Very little research exists about how environment affects snakes’ brains directly. This article looks at the neurological benefits of enrichment in other species and makes the case to extend what we know about them to snakes.
This review investigates possible neural consequences of captive environments on snakes under human care. The impact of captive environments on behavioral and physical health, development, and overall welfare has been studied and well-documented in a wide range of species including humans, other mammals, insects, birds, and fish. While there has been some research with respect to this in snakes and other reptiles, that research is focused on how environmental complexity or lack of complexity impacts behavior, activity level, problem-solving, and response to novelty, but it has not looked specifically at how the brain structure itself may be impacted.
Reptiles in general, and snakes specifically, are often left out of consideration when training and enrichment programs are developed at zoos, sanctuaries, rescues, shelters, research laboratories, breeding facilities, and in private homes. Psychological and neurological health are key to overall optimal welfare, as these can impact physical and mental health of snakes held in captivity.
In this paper, I explore the possible neural consequences for snakes living in captive environments, focusing on the effects of environmental impoverishment or enrichment on brain structure. My conclusion supports the hypothesis that there is an impact on the brains of snakes because of the captive environment they are exposed to during development and the environment they routinely live in as adults.
It has been a popular belief that snakes and other reptiles lack the brain structure of mammals and are incapable of emotion or complex cognition. This is due in part to Paul MacLean’s “triune brain” concept introduced in 1957, which theorized the human brain was built of newer pieces that arose in mammals and was not present in the reptiles that came before.1 Gilles Laurent published a 2018 study positing that MacLean’s theories about the divisions of reptile and mammalian brains were incorrect.2 Earlier research supports this, indicating that brain structures are highly conserved across vertebrates,3 and that reptiles share the same or homologous brain structures as other vertebrates.4
Snakes’ brains, like those of other vertebrates, are divided into the forebrain, midbrain, and hindbrain. The forebrain regulates functions such as taste, smell, and sensorimotor integration and mediation; it includes the telencephalon and diencephalon (hypothalamus, thalamus, infundibulum, pituitary gland, pineal complex). The midbrain regulates neuroendocrine functions and visual processing, and the hindbrain controls hearing, balance, and physiological homeostasis.5
There is a large body of research in the scientific literature regarding the ways in which living in deprived environments versus environments composed of complexity and mental stimulation impact brain structure and cognition. There is evidence that neuroplasticity occurs not only during development but in adult animals as well. Research indicates that adult neurogenesis does occur, not only in mammals and birds but also in amphibians, reptiles, and bony fishes.6 The brain’s responsiveness to environmental stimuli as an indication of neural plasticity has been demonstrated across all species examined to date, including insects such as honeybees,7 other invertebrates,8 mammals,9 fish,10 and reptiles.11
Contrary to what many people have historically believed, complex cognitive processes are found across a wide variety of taxa, from fish and insects to birds, mammals, and reptiles. What we know about the neuroanatomy of snakes supports that they are capable of neuroplasticity, and that their brains will change in response to their environment.”
Captive conditions for snakes
Snakes living under human care are often kept in deprived environments, without the ability to express species-typical behavior and lacking opportunities to learn novel behaviors through exposure or training.12 The physical, cognitive, and neural consequences of environment are well-documented across species, and evidence suggests the neural impacts of environment on the brain are well-conserved across vertebrates. Therefore, the potential neural consequences of snakes living in captive environments, including how environmental impoverishment versus enrichment impacts the brain, are likely the same or similar. This has been demonstrated in studies with cornsnakes,12,13 rat snakes,14 Burmese pythons,15and Madagascar giant hognose snakes16 as examples. The detrimental neural consequences of impoverished environments and the neural consequences of stress on the brain may also contribute to stereotypies (Burghardt, 2013)17observed in captive snakes as a manifestation of neurological functioning and coping.
Snakes are kept by commercial breeders, research labs, zoological institutions, animal rescues and sanctuaries, animal shelters, pet shops, schools, private keepers, and pet owners. Housing for snakes under captive management is not uniform. Snakes are kept in conditions ranging from racks18 consisting of snakes in plastic drawers to elaborate naturalistic, complex, and enriched habitats, and variations in between.18 Guidelines, regulations, and standards vary by country, industry, and context; and do not exist at all in some places. These circumstances create disparate environments for captive snakes around the world, with some exposed to cognitive stimulation and opportunities for exercise and others maintained storage containers with nothing but access to water and necessary heat.
For the purposes of this review, “complex and enriched environments” will refer to those with access to simulated natural light and heat, multiple options for the snakes to move, the ability to exhibit species-typical behaviors, and opportunities to experience novelty. An example of these conditions would be a habitat as long or longer than the length of the snake with multiple levels, varied substrates, multiple climbing, hiding, or burrowing options, climate gradients, the ability to see out and observe the external environment, and the periodic introduction of novel items inside the habitat.
“Impoverished, deprived, and standard environments”14 will refer to those conditions where the snake has limited space to move, is unable to exhibit a range of species-typical behaviors, is not exposed to novelty, has no access to simulated natural light or heat from above, cannot see out, and in general has limited opportunity to experience physical exercise or cognitive stimulation. An example of these conditions would be a living space with paper for substrate, a water dish, opaque walls, a warm and cool side, limited to one level, and insufficient space to fully stretch out their body length.
Behavioral consequences of captive environments for snakes
In addition to the plethora of studies in mammals, other vertebrates, and humans demonstrating the effects of impoverished versus enriched environments on development and cognitive abilities, there have been a few done specifically with snakes.
A 2006 study by Almli and Burghardt done with ratsnakes demonstrated that housing conditions affected their behavior. They divided subjects into two groups, housing one group under enriched conditions that included loose substrate, multiple hides, climbing opportunities, and a rock, and one group under standard conditions that included paper substrate, one hide, and a water dish. The enriched-condition snakes performed better in a problem-solving task, in an open-field task, and were more behaviorally adaptive than the standard-condition snakes.14
A study published in 2021 by Hoehfurtner indicated that an environmentally complex enclosure benefitted the behaviour and welfare of captive corn snakes.12 Another 2021 study with cornsnakes determined that enrichment impacts performance during odor discrimination tasks; snakes were able to discriminate between familiar and unfamiliar humans, but only when living in enriched conditions.13
The Reptile Conservation Center at the Detroit Zoo recently did a habitat comparison study and determined that Madagascar giant hognose snakes showed increased behavioral diversity and overall activity levels when housed under complex conditions versus standard conditions.16
Demonstrating that snakes have the capacity for complex learning, Emer et al. in a 2015 study trained wild Burmese pythons using the same principles of learning theory and operant conditioning used for mammals, to learn a complex food-acquisition task. The snakes demonstrated complex cognitive abilities by learning how to press a button to gain access to food but only when the button was illuminated by a green light.15 When exposed to training and general cognitive stimulation snakes are able to learn and perform complex tasks, failure to provide these opportunities has demonstrated reduced cognitive abilities as in the inability of cornsnakes living in standard conditions to discriminate between familiar people or strangers while those living in enriched conditions were able to.13
Behavioral welfare is also impacted by the conditions in which snakes are maintained. Snakes exhibit individual- and species-level temperament and personality differences, varied cognitive and learning capacities, and a need for stimulation.19 When housing conditions do not support these needs and abilities, maladaptive behaviors or stereotypies may surface in an attempt by the snake to cope with the lack of opportunities to express natural, species-typical behaviors.5 When snakes are motivated to do a behavior that their environment or circumstances prevents them from being able to do, stereotypies may develop which can include nose rubbing, escape behaviors, edging, hyperactivity or lethargy, striking at movement, nose or body pushing, tail whipping, excessive soaking in water, or stargazing.
Neural impact of deprived environments
Decades of studies across species into the neural impact of complex/enriched versus deprived/impoverished environments provide evidence for functional, anatomical, chemical, and molecular effects to the central nervous system (CNS) by environmental conditions.20 In a 2021 paper by Jacobs and colleagues, a detailed compilation of evidence is provided indicating epigenetic changes in response to environmental enrichment or impoverishment as well as stereotypies induced by impoverishment and prevented or stopped by enrichment across species.20
Neurons are specialized communication cells that pass along information electrically and chemically within the brain and to the rest of the CNS. Synapses are the connections or intersections between neurons where this communication occurs. Synaptic plasticity is the ability of the neurons to change in response to experience, cognitive stimulation, and learning. This neuroplasticity is possible not only in developing organisms but in adults as well.21 When neurons repeatedly communicate with each other their efficiency increases, and when there is a lack of communication between two neurons efficiency in that area of the brain decreases. The more efficient the communication between neurons the more learning will occur. The receiving neuron becomes more sensitive, structural changes strengthen the existing synaptic connections and form new dendritic branches, ultimately building new connections.
Hebb’s postulate of synaptic change — Hebb’s Rule — states that “neurons that fire together wire together.” It has long been a foundation in neuroscience. Over the years Hebb’s postulate has been built on and combined with new knowledge about neuroplasticity;22 however, the basic premise that unused neural pathways diminish and atrophy, and well-used neural pathways are strong and thrive holds true for work in animal behavior, training, and welfare science.
Physically and mentally stimulating environments will support greater neuroplasticity, which in turn results in greater cognitive abilities. The current body of research supports that impoverished and enriched environments have a neural impact on the brain. Impoverished captive environments create cortical changes such as decreased cortical thickness, smaller capillary diameter, decreased neuronal soma size, fewer glial cells per neuron, less complex dendritic branching, fewer dendritic spines, and less efficient synapses.21
Since snakes share the same neural structure, including that of the brain and central nervous system, as all vertebrates and because there is an established link between stimulation, neuroplasticity, and cognition, we can postulate that enriched environments for snakes could lead to, for example, increased frequency of exploratory behaviors, and/or a greater engagement with training, and increased interest in their human caregivers. A deprived environment, in contrast, could lead to stereotypical behaviors or learned helplessness.
Considering Other Impacts
Research across species indicates that there are molecular impacts to animals developing in or living in impoverished versus enriched environments. Levels of acetylcholine, monoamines, noradrenaline, serotonin, amino acid transmitters, nerve growth factors, and brain-derived neurotrophic factor are all affected by the environment.21
Levels of these neurochemicals and hormones play a role in physical and psychological health. Acetylcholine is a key neurotransmitter, communicating electrochemical messages between neurons. Monoamines are neurotransmitters that function in modulating psychomotor function, sleep, hormone secretion, body temperature, and pain. They also play a role in cardiovascular, respiratory, and gastrointestinal functioning.23 Monoamines include serotonin, as well as the catecholamines: dopamine, adrenaline, and noradrenaline.
Neurochemicals work in coordination with others to regulate the body as a whole. None of them function alone.24 When levels of these neurochemicals and hormones are not optimal or become dysregulated, physical health, stress response, and coping abilities will be impacted.
What this means for snakes, just like for other vertebrates, is that levels of neurochemicals and hormones will be diminished when the body and brain are not stimulated to produce them.
Animals evolved to move. Animals in the wild physically move to locate resources such as shelter, food, water, and mates, and to escape predation. When snakes under captive management no longer must use 100% of their energy budget on survival and reproduction, they will find other things to do. When they are unable to use up this energy performing natural behaviors, stereotypies and other maladaptive behaviors may develop as an attempt to cope. In addition to mental exercise, physical exercise is integral to optimal welfare for captive snakes.
Exercise increases the flow of oxygenated blood to the brain, as well as serum neurotrophic factors and brain-derived neurotrophic factor. This supports neurogenesis and enhanced cognitive abilities.20 Exercise positively affects the immune system, leading to reductions in inflammatory biomarkers and increases in antioxidant defenses. This may enhance the activity of several neurotransmitter systems.20
Snakes in the wild spend time engaging in exploratory locomotor activity such as searching for food and other resources. Stress is created under captive management when snakes lack adequate opportunities for exercise and cannot assume a straight-line body posture.5 Lack of exercise opportunities and adequate space resulting from deprived captive living environments limits muscle development and cardiovascular fitness, and the inability to stretch out rectilinearly may cause snakes kept in small containers to experience digestive issues and coelomic discomfort .5
This means that exercise is not only beneficial for humans and other animals but for snakes as well. Captive snakes with the opportunity to maintain physical fitness through exercise will likely develop greater muscle mass, less fat, more stamina, and have improved cardiac health.
Stress and coping
Wild animals evolved to cope with adversity by means of a stress response. Stress is adaptive and functions to help animals survive in the moment when confronted with a threat, danger, or in survival situations. Stress in snakes, as in other vertebrates, activates the sympathetic nervous system. The hypothalamus pituitary adrenal (HPA) axis is activated because of the body’s neuroendocrine response.5 This process regulates physiologic functions, making things like running and fighting easier for the animal while slowing or shutting down systems not needed for survival in the moment, such as digestion and reproduction. For snakes this means when they experience a fight or flight stress response their bodies are channeling resources to their muscles for a fast escape or a powerful offensive strike.
Glucocorticoids are released during this process, which is beneficial for short-term survival but not needed for day-to-day existence. According to the behavioral health section in Mader’s Reptile and Amphibian Medicine and Surgery, many behavioral changes observed in captive snakes are a result of this stress response becoming maladaptive due to the captive experience. Snakes evolved to cope with acute occurrences of stress that may include real or perceived threats; however, when the day-to-day living conditions are the source of constant stress that the snake is unable to change or escape from, they experience chronic stress, causing abnormal behaviors, health issues, and disease.5 When stress levels exceed the ability of the snake to cope with the stressor(s), the constant elevated levels of stress hormones impact the brain, reducing flexibility, impairing learning, and dysregulating the normal stress response.25
The amygdala plays a major part in processing sensory information and regulating emotional responses. Prolonged stress can cause morphological changes to the amygdala including increased dendritic complexity and spine density in areas likely to cause increased stress reactions and greater likelihood of generalized fear, while neurons in regions that regulate emotion show decreases in dendritic branching and spine density.26,27
In addition to stereotypies caused by the lack of physical exercise as mentioned earlier, stress can also play a role in the manifestation of stereotypies as a neural attempt to cope with the chronic psychological distress caused by an impoverished environment.20
This means when captive snakes are experiencing perceived threats such as unfamiliar motion outside of their enclosures, forced handling, or exposure to novelty without prior desensitization to novelty in general, the stress response is activated, and the areas of the brain involved in fear learning and anti-predator responses are being engaged. If this is the only stimulation the snake is experiencing on a regular basis, they may develop chronic stress leading to generalized fear and anxiety (the expectation that something aversive will happen in the future) and poor physical health from the constant or frequent elevation in stress hormones. When snakes engage in regular exercise, cognitive stimulation, training, and gradual desensitization to novelty the brain areas that regulate emotions and inhibit fear generalization are engaged, reducing the likelihood of animals with high general anxiety and reactivity and increasing the likelihood of animals having increased coping abilities and resilience.
Evidence supports that the neuroanatomy of snakes consists of the same or homologous structures as other vertebrates, that the same or homologous neurochemicals and hormones are produced, and that the structures and functions of the central nervous system are well-conserved across vertebrate species, including snakes. Numerous studies have been conducted regarding the impact of impoverished and enriched environments, and all point to the fact that environmental complexity and cognitive stimulation enhances growth, problem-solving abilities, general cognition, stress coping, resiliency, general health and fitness, and overall well-being. These studies have been done in species that include mammals, birds, fish, reptiles, and invertebrates. While evidence points to snakes being impacted similarly to other species, more research is needed to expand knowledge in this area specifically with snakes. The studies with snakes that have been conducted support the idea that enriched environments should be a component in optimal welfare for snakes under captive management, but these studies need to be replicated with additional snake species and built on to gain a more specific understanding of how environment impacts development and continued psychological health and growth in snakes.
This review of prior research supports the hypothesis that snakes under captive management sustain impoverishment-related neural deficits and dysregulation, like other vertebrates, when maintained in deprived rather than enriched conditions. Snakes have the same or homologous neurobiological systems that are well-conserved across vertebrate species, including systems for coping with stress. Snakes display behavioral patterns and physical abnormalities equating to those of other vertebrates maintained in impoverished environments. The brains of snakes housed in deprived versus cognitively complex environments are likely affected in a manner similar to other species studied under similar conditions. The evolutionary continuity of neural structures existing across vertebrates supports this conclusion.
Research supports the idea that snakes under captive management maintained in impoverished conditions likely experience poor welfare, and the hypothesis about neural damage is likely valid. In contrast, research indicates that snakes under captive management maintained in enriched environments likely experience good welfare resulting in neural growth and improved cognition.
Evidence suggests that snakes maintained under captive management should be housed in habitats with environmental complexity promoting mental stimulation, physical exercise, and that provides opportunities to engage in species-typical behaviors. They should also have space to stretch out the length of their body rectilinearly, be provided with opportunities for cognitive growth through training and/or exposure to novelty, and be exposed to achievable challenges to build resilience.
Here’s a video version of this article:
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Lori Torrini is the director of Spirit Keeper Equine Sanctuary 501c3 where, in addition to special needs horses, they care for dogs, cats, pigs, goats, chickens, snakes, and miscellaneous other species in need of their services. Lori also runs her own animal training and behavior consulting business, Behavior Education LLC with the majority of her clients over the last 4 years being snakes; however, she still works with dogs, cats, horses, and other reptiles. Lori has an associate of science degree in Zoo Keeping Technology from Pikes Peak Community College and a certificate in Applied Animal Behavior from the University of Washington. She is a certified animal trainer through CCPDT and a Fear Free Certified Professional Trainer. Lori has completed the 8-week Living and Learning with Animals and How Research Works professional development courses through Dr. Susan Friedman’s Behavior Works, the AZA Animal Training Applications in Zoos and Aquariums professional development course at the Denver Zoo, and the Animal Welfare Professional course through San Diego Zoo Global Academy. Prior to her current work Lori worked for 29 years as a veterinary assistant and receptionist in Colorado Springs and was the City of Colorado Springs Animal Emergency Response Coordinator from 2009 – 2013.
Good to see the material covered in Jacobs et al. (2021) extended to reptiles!