Brain size

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 (Manger et al., 2009. 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 (Manger et al., 2013). 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 (Cozzi et al., 2001; Shoshani et al., 2006). 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 (Jerison, 1973). 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 (Roth & Dicke, 2005).

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 (Shoshani et al., 2006). The EQ ranges from ~1.13 to ~2.36, with an average of ~1.88 (Shoshani et al., 2006). 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.

The figures for elephants are comparable to the larger primates (e.g., chimpanzee: 2.2-2.4; gorilla: 1.4-1.7; orangutan: 1.6-1.9, although Homo sapiens at 7.0+ is far above all other mammals). The EQ for cetaceans ranges from about 1.5 in river dolphins to as high as 5.6 in bottle-nosed dolphins, which is about the same as Australopithecines. Gross relative brain size provides only a small window into intelligence, which is too complex to be characterized by a single numerical index.

Size differences aside, all eutherian mammals share the same brain components (Finlay & Darlington, 1995), with many parts of elephant brains appearing to be highly conserved in terms of neuroanatomy and chemoarchitecture (Denver, 2009; Jacobs et al., 2011). Indeed, the modern African elephant brain appears to share many neuroanatomical features with the brain of the woolly mammoth from ~39,000 years ago (Kharlamova et al., 2015). The internal structural complexity of individual parts of the brain is probably a more important factor in the evolution of intelligence.

Elephant cerebral cortex and neuronal characteristics

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; Herculano-Housel et al., 2014). 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 (Hart et al., 2008).

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 (Barasa & Shochatovitz, 1961). 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 (Manger et al. 2008), and a lack of well-preserved elephant brain tissue suitable for histological analysis. This latter issue was recently addressed by Manger et al. (2009), 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. More recent investigations by Jacobs and his colleagues (2011 paper linked in right frame) have explored for the first time the neuromorphology of elephant cerebral cortex. In general, there appear to be a great diversity of neurons in the elephant neocortex, which exhibits very large and complex neurons, some of which differ in fundamental ways from those observed in primates (including humans). More specific findings are highlighted in the figures you will find linked in the right frame, with explanations in the figure captions. Elephant neuroanatomy… - what different areas of the brain reveal Several areas of the elephant brain have now been examined in some detail. Temporal lobes and hippocampus. 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. In a recent MRI study, Hakeem et al. (2005) noted that elephants appear to have somewhat large and highly convoluted hippocampus, although more a more recent study suggests that the elephant hippocampus is about what one would expect in a brain of this size (Patzke et al., 2013). Hakeem et al. 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.

Scientists are beginning to unravel the mysteries of the elephant brain. Click on the figure above and you will see some fascinating images from the brain of an elephant preserved for research purposes. The images are related to the paper linked below.   Neuronal morphology in the African elephant (Loxodonta africana) neocortex. (1.96 MB), by Jacobs, Lubs, Hannan, Anderson, Butti, Sherwood, Hof & Manger, was published online 16 November 2010. You may like to read the article "What elephants' unique brain structures suggest about their mental abilities" in THE CONVERSATION, 8 August 2018, to a large extent based on the same investigations.

Corpus callosum

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 (Manger et al., 2010). 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.

Cerebellum

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 (Maseko et al., 2012), a finding typically explained with reference to the fine motor control demands of its trunk (Maseko et al., 2012). 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 (Bower, 1997) - 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 (Rasmussen & Munger, 1996). By extension, the auditory-tactile infrasound information perceived through the elephant’s feet may also contribute to its enlarged cerebellum (Soltis, 2009) - much as echolocation may increase the size of the cerebellum in odontocetes.

Olfactory bulbs

The olfactory bulbs are involved, as the name implies, in the sense of smell. They are extremely large in elephants (Ngwena et al., 2011). 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 (von Dürckheim et al., 2018), 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; Bates et al., 2007), 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 (Plotnik et al., 2019), a feat that humans are unable to do.

Amygdala

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 (Patzke et al., 2015). 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 (Limacher-Burrell et al., 2017). The relatively large size of other amydaloid subnuclei, in conjunction with the hippocampus, underscores the strong role that emotions play in memory formation (Limacher-Burrell et al., 2017). 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.

Brainstem and diencephalon

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 (Maseko et al., 2013). Brainstem regions involved in sound production and reception are also quite large, underscoring the fundamental importance of vocal communication in elephants (Maseko et al., 2013).

Trigeminal system

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 (Purkart et al. 2021). 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.

How intelligent are elephants?

Clearly, much more research is needed before we understand the significance of these cellular characteristics in elephants. But the research appears to be well underway, and those who have had the privilege of examining the elephant brain agree that it is a magnificent collection of very intricately connected neurons. Certainly, the complexity of the elephant brain provides support for elephant intelligence. Read more under Elephants are intelligent.

Bob Jacobs talking about the amazing brains of elephants on documentary Mind of a Giant from 2016.