The Elephant Brain

The elephant brain, at approximately 5,000 grams, is among the largest of any land mammal and exhibits striking structural complexity. Research demonstrates a highly expanded and intricately folded neocortex, an exceptionally large cerebellum, and well-developed sensory and emotional processing structures, including the amygdala and associated nuclei.

Encephalization quotient values place elephants within the range of great apes and some cetaceans, highlighting their substantial neural investment beyond basic bodily functions. Together these anatomical feature help explain elephants’ advanced cognitive and social abilities.

Size of the Elephant Brain Elephant cerebral cortex and neuronal characteristics Temporal lobes and hippocampus

With a large body comes a large, complex brain. The elephant brain, at ~5,000 grams, is among the largest on the planet and is evolutionarily adapted to flourish in a complex, stimulating environment. Indeed, elephants and ~75% of cetacean species (i.e, whales and dolphins), along with humans and three pinniped species, belong to a small subset of species with brain masses >700 grams. Until recently, very little was known about the elephant brain. There were only a few original articles had specifically focused on the elephant central nervous system. The brains of Asian (Elephas maximus) and African (Loxodonta africana) elephants rank among the highest for absolute and relative mass, and for cortical expansion. Their brains exhibit features comparable to those of some of the cetaceans and the great apes, including humans. The brain of a newly born elephant is approximately 50% its adult weight, indicating a prolonged neurodevelopmental period wherein the environment will significantly shape the intricate neuronal microstructure.

One way of comparing the brains of different animals is to use the Encephalization Quotient (EQ). EQ is the ratio of the observed brain mass to the expected brain mass of a typical animal of that size. Looking at brain size in this way, an EQ equal to 1.0 is an average mammalian brain. Theoretically, the larger the brain is relative to body size, the more the neural resources there are to go beyond basic survival tasks (e.g., breathing, motor skills) into more complex cognitive functions. The elephant brain is slightly larger than expected for its body size.

During evolution, the EQ of the Proboscidea has increased by 10-fold, from 0.2 for extinct Moeritherium, to about 2.0 for extant elephants. The EQ ranges from ~1.13 to ~2.36, with an average of ~1.88. Asian elephants appear to have a higher average EQ than African elephants, at 2.14 and 1.67, respectively — although these figures are based on a very small sample size. In species where sexual dimorphism is pronounced, as in elephants, males have lower EQ values than females (EQ African elephant: male: ~1.3 — female: ~2.0). So, it is clearly important to know which sex is being measured as this may also affect observed estimates.

Elephant cerebral cortex & neuronal characteristics

Golgi stain of elephant cortex under the microscope.

The cerebral cortex (or neocortex) is the outermost ribbon of nerve cells in the brain responsible for sensory elaboration and cognitive capacity (e.g., working memory, planning, decision making, spatial orientation, speech and language). Elephants have a large and highly convoluted neocortex, with the greatest volume available for cognitive processing of all land mammals. The volume of elephant neocortex relative to the rest of the brain ("neocortex ratio") has been shown to correlate closely with social group size, suggesting that it underwrites the cognitive skills needed for complex social living.

Moreover, the finding that neocortical ratio predicts the frequency with which primate species have been found to use tactical deception to solve social problems lends support to this argument. These cortical characteristics suggest a very elaborated sensory information/cognitive processing system.The African elephant brain contains ~257 billion neurons, three times as many as the ~86 billion neurons in the adult human brain, with ~25 billion (or 97.5%) of these neurons in the cerebellum (compared to ~69 billion in the human) and only 5.6 billion in the neocortex (compared to 16.3 billion in the human. It should be noted that elephant neocortex appears to have a relatively low density of neurons, suggesting that the elephants' cognitive faculties may be concentrated in long-term processing and in synthesizing a great diversity of input over time.

Until recently, the only insight into elephant cortical neuromorphology (i.e., the shapes and types of nerve cells) was a single drawing from an Asian elephant. Reasons for this poverty of data are many, but include a propensity for neuroscientists to focus on the rodent and primate species commonly used in biomedical research, and a lack of well-preserved elephant brain tissue suitable for histological analysis. This latter issue was recently addressed by, who were able to perfusion fix the brains of wild African elephants. As a result, neuroscientists have begun to explore the neural components of the elephant brain in more detail.

A procession of elephants in Amboseli - the large size of the temporal lobes and hippocampus may explain their prodigious memories and their ability to navigate over long distances.

One area of particular interest in the elephant is the temporal lobes and the underlying hippocampus, which are crucial to (declarative) memory functions, particularly of a spatial nature. An MRI study noted that elephants appear to have somewhat large and highly convoluted hippocampus, although a more recent study by Patzke and team suggests that the elephant hippocampus is about what one would expect in a brain of this size. Hakeen and coauthors estimated that the elephant hippocampus takes up 0.7% of the central structures of the brain in elephants, as compared to only 0.5% in humans. Although the hippocampus is necessary for laying down new memories, the memories are not stored there. Instead, they are stored in the surrounding temporal lobes, which are particularly large and distinct in the elephant. The relative size of these two structures may explain their prodigious memories (for places, individuals, and events) and their ability to navigate over long distances.

An adult male and a young adult female illustrating sexual dimorphism in elephants

The corpus callosum is the main fiber tract that connects the two cerebral hemispheres. Although it has the largest absolute size recorded to date, the relative size compared to the rest of the brain is what one would expect in a brain of this size. The preliminary data also indicate a possible sexual dimorphism (females > males) in the size of the corpus callosum, which would suggest that elephants are the first non-primate to exhibit this sexual dimorphism.

The cerebellum, which is intimately involved in coordination, is very large in elephants (thus explaining the extremely high number of cerebellar neurons). In fact, the elephant possesses the largest absolute and relative cerebellar volume of any mammal investigated to date, a finding typically explained with reference to the fine motor control demands of its trunk. However, the underlying explanation for such a large cerebellum may be much more complex insofar as cetaceans also have a very large cerebellum even though they don’t have a trunk or hands (like humans) that require complex motor dexterity.

It appears that cerebellar function may extend beyond simple motor control to total body engagement in monitoring and adjusting the acquisition of sensory information for the rest of the nervous system - i.e., the body’s interface with the surrounding environment. As such, the cerebellum plays a critical role in the trunk’s multi-sensory exploration of the environment. By extension, the auditory-tactile infrasound information perceived through the elephant’s feet may also contribute to its enlarged cerebellum - much as echolocation may increase the size of the cerebellum in odontocetes.

The olfactory bulbs are involved, as the name implies, in the sense of smell. They are extremely large in elephants. In fact, they are approximately the size of the palm of the human hand; by comparison, a deer or large dog olfactory bulb is about the size of a human finger.The human olfactory bulb is only the size of a cotton swap (e.g. a Q-tip). These enlarged olfactory bulbs explain why the elephant has such an acute sense of smell, one that is many times more sensitive than that of a bloodhound.

This finely tuned sense of smell is crucial for elephants, who used olfactory cues to find food, to classify predators (including human ethnic groups), to detect potential mates, and to traverse diverse landscapes over long distances that are rich with olfactory information. Elephants are even able to use smell to detect different quantities of a substance such as sunflower seeds, a feat that humans are unable to do.

The amygdala is involved in evaluating incoming sensory information on an emotional level, especially with regard to the emotion of fear. Although the volume of the elephant amygdala is a large, it is within the range of what one would expect in such a large brain. Nevertheless, the topological arrangement and relative size of some of the subnuclei (i.e., clustered groups of neurons that share the same function) in the elephant amygdala are unusual in comparison to other mammals. Subnuclei involved in the processing of emotional aspects of sensory information are particularly large; olfactory input appears to be very important in generating emotional states in the elephant.

The relatively large size of other amydaloid subnuclei, in conjunction with the hippocampus, underscores the strong role that emotions play in memory formation. In an animal with such rich conspecific interactions, a relatively large amygdala and associated neural structures would be essential for normal social functioning as well as for evaluating potential dangers in the environment.

Although similar in many ways to what one observes in other mammals, there are many specializations (i.e., nuclei) in these subcortical structures. As one might expect, the nuclei involved in controlling movements of the trunk are quite elaborated. Brainstem regions involved in sound production and reception are also quite large, underscoring the fundamental importance of vocal communication in elephants.

The trigeminal nerve is a cranial nerve that, among other functions, receives sensory information from the face and, in the elephant, crucially, from the trunk. In elephants, not surprisingly, this nerve and its associated ganglia, are extremely large. In fact, the nerve connections to the trunk are more substantial than the nerves to the rest of the elephant body. The sensory component of trunks is thus every bit as sensitive as the motor component is articulate.

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Bates LA, Poole JH, Byrne RW. 2007. Elephant cognition. Curr Biol. 17(16):R544–R546. https://doi.org/10.1016/j.cub.2008.04.019

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