Pioneering research explores shapes and size of neurons in the elephant’s cortex
TODAY is World Elephant Day, which raises awareness of conserving these majestic animals.
Elephants have many engaging features, their incredibly dexterous trunks and memory abilities make them complex social animals.
But there is much less discussion of their brains, even though such a large animal has a pretty big brain (about 5.4kg).
Until recently very little was actually known about the elephant brain. That door was opened by the pioneering efforts of neurobiologist Paul Manger at the University of the Witwatersrand, who obtained permission in 2009 to extract and preserve the brains of three African elephants scheduled to be culled.
The research was conducted at Colorado College in 2009-2011 in co-operation with Manger, Columbia University anthropologist Chet Sherwood and neuroscientist Patrick Hof of the Icahn School of Medicine at Mount Sinai.
The goal was to explore the shapes and size of neurons in the elephant cortex.
The cortex constitutes the thin, outer layer of neurons (nerve cells) that cover the two cerebral hemispheres. The arrangement and morphology of neurons is relatively uniform across mammals – or so we thought after decades of investigations. It found the morphology of elephant cortical neurons is different from anything we had ever observed before.
The process of exploring neuronal morphology begins with staining brain tissue after it has been fixed (chemically preserved) for a period of time. In our laboratory, we use technique called the Golgi a stain, named after Italian biologist and Nobel Laureate Camillo Golgi (1843-1926).
The Golgi stain impregnates only a small percentage of neurons, allowing individual cells to appear relatively isolated with a clear background.
This reveals the dendrites, or branches, that constitute the receptive surface area of these neurons.
The dendrites allow the cell to receive and synthesise incoming information from other cells. Once we stain neurons, we can trace them in three dimensions under the microscope. Here are three major differences that we found between cortical neurons in the elephant and in other mammals.
First, the dominant cortical neuron in mammals is the pyramidal neuron.
These are also prominent in the elephant cortex, but they have a very different structure. Instead of having a singular dendrite that comes off the apex of the cell (known as an apical dendrite), apical dendrites in the elephant typically branch widely as they ascend to the surface of the brain.
Second, the elephant exhibits a wider variety of cortical neurons than do other species. Some of these, such as the flattened pyramidal neuron, are not found in other mammals.
One characteristic of these neurons is that their dendrites extend laterally from the cell body over long distances.
Third, the overall length of pyramidal neuron dendrites in elephants is about the same as in humans. Human pyramidal neurons tend to have a large number of shorter branches, whereas the elephant has a smaller number of much longer branches.
In terms of cognition, my colleagues and I believe that the integrative cortical circuitry in the elephant supports the idea that they are essentially contemplative animals.
Observations of elephants in their natural habitat by researchers such as Dr Joyce Poole suggest that elephants are indeed thoughtful, curious and ponderous creatures.
Their large brains appear to provide the neural foundation of the elephant’s sophisticated cognitive abilities, including social communication, tool construction and use, creative problem-solving, empathy and self-recognition, including theory of mind.
The special morphology of elephant cortical neurons reminds us that there is certainly more than one way to wire an intelligent brain.
* Jacobs received his PHD in Applied Linguistics at UCLA, where he worked with John Schumann and Arnold B Scheibel.
He has lived in Germany, Japan, and China. He became a member of the Colorado College Psychology Department in 1993 and developed the neuroscience major in 1996.
His research interests include language acquisition, non-human animal communication, cognitive neuroethology and comparative neuroanatomy.
Most recently, he has been conducting collaborative quantitative neuromorphological research on several more exotic species: elephants, humpback whale, giraffe, manatee and Siberian tiger. – The Conversation