Brain Cells for Socializing

Does an obscure nerve cell help explain what gorillas, elephants, whales—and people—have in common?

John Allman (with colleague Atiya Hakeem at Caltech examining elephant brain specimens) is searching for one of the biological keys to human behavior. (Aaron Huey)
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Allman thinks that the neurons expedite communication from the ACC and FI to the rest of the brain. The cells are unusually large, and in the nervous system, size often correlates with speed. "They're big neurons, which I think do a very fast read of something and then relay that information elsewhere quickly," he says. He speculates that as our primate ancestors evolved bigger and bigger brains, they needed high-speed connections to send messages across greater distances. "Large brain size necessarily carries with it a slowing down of communication within the brain," he adds. "So one way of dealing with that is to have a few specialized populations of cells that are pretty fast."

Given that the neurons live in the brain's social hot spots, Allman theorizes that the von Economo cell system allows a rapid, intuitive read on emotionally charged, volatile situations. The neurons "would enable one to quickly adjust to changing social contexts," he speculates. In the ancient past, this neural wiring might have conferred a survival edge to our ancestors by enabling them to make accurate, split-second judgments, especially about whom they could trust or not.

Allman, Hof and their colleagues have looked for von Economo neurons in more than 100 animal species, from sloths to platypuses. Only a few of them, other than primates and elephants, are known to have the cells: humpback whales, sperm whales, fin whales, orcas and bottle-nosed dolphins. The cells presumably evolved in now extinct species that gave rise to those marine mammals some 35 million years ago.

As I watched him section the elephant brain at Caltech, Allman, with colleagues Atiya Hakeem and Virginie Goubert, finally reached the FI of Simba's left hemisphere. Three days later, microscope examination of the brain slices revealed it to be dotted with the distinctive spindle-shaped cells. That confirmed their previous sighting of similar neurons in the FI of Simba's right hemisphere. The elephant cells are larger than human and primate ones, about the size of whale neurons, but the size and shape are unmistakably von Economo neurons.

From counting the von Economo cells in 16 slides—an eye-glazing chore—Hakeem and Allman estimate that there are roughly 10,000 of them in the postage-stamp-size FI on the right side of the elephant brain, or about 0.8 percent of the FI's 1.3 million neurons. Von Economo neurons are more plentiful in the human FI, averaging about 193,000 cells and accounting for about 1.25 percent of all neurons there. In absolute numbers, the human brain has roughly half a million von Economo neurons, far more than the brains of elephants, whales or great apes. Allman and his colleagues have found none in the elephant's closest kin: the anteater, armadillo and rock hyrax. The cells' absence in these species supports Allman's theory that the neurons are a feature of big brains.

Allman speculates that such cells readily evolve from a small set of neurons in the insular cortex that are found in all mammals and regulate appetite. He thinks that while von Economo cells likely evolved to speed information around a big brain, they got co-opted by the demands of social interactions. If he's right, smart, social animals such as whales and elephants might have the same specialized wiring for empathy and social intelligence as human beings.

Whales and elephants, like people and great apes, have large brains and a prolonged juvenile stage during which they learn from their elders. They recognize one another and develop lifelong cooperative relationships. Killer whales hunt in groups and protect injured pod mates. Elephant society is anchored by matriarchs that guide their herds to watering holes they know from previous visits. (And there may be some truth to the belief that elephants never forget: when Allman, Hof and Hakeem made the first high-resolution 3-D image of an elephant brain, in 2005, they found an enormous hippocampus, the brain region where memories are formed.) The sensitive beasts identify each other by their rumblings and trumpet calls, come to each other's aid and seem to mourn their dead.

Allman likes to show a clip from a documentary about a group of African elephants that adopted an orphaned calf. When the baby elephant falls into a water hole, the matriarch quickly marches in, followed by the others. Together she and a second female use their tusks, trunks and legs to free the calf from the muck. Another animal paws at the steep bank with its foot, building a ramp the youngster uses to climb to safety. "It's really remarkable," says Allman of how the elephants rapidly sized up the crisis and worked together to save the baby. "It's a very high sort of functioning that very few animals are able to do. And," he adds with a chuckle, "humans can do it only on good days." The rescue, he says, "captures the essence of really complex, coordinated social behavior."

The idea of the neurons' centrality to social intelligence is gaining ground. Yerkes primatologist Frans de Waal says Allman's "extremely exciting" research dovetails with some of his own investigations of pachyderm intelligence. Two years ago, de Waal and two collaborators reported that a Bronx Zoo elephant named Happy could recognize herself in a mirror. Some scientists theorize that the ability to recognize one's own reflection indicates a capacity for self-awareness and even empathy, useful skills in a highly social species. De Waal points out that only animals that have von Economo neurons can do so.

Yet de Waal also cautions that "until someone establishes the exact function of those cells, it remains a story, basically."


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