91av

THEY were touted as the brain cells that set humans and the other great apes apart from all other mammals. Now spindle neurons – the specialised brain cells thought to process our emotions and that may even enable us to love and suffer – have been found in whales. The discovery will stimulate debate both on the level of whale intelligence and on the ethics of hunting them.

Spindle cells, named for their long, spindle-shaped bodies, occur in the parts of the human brain linked with social organisation, empathy, speech, intuition about the feelings of others and rapid “gut” reactions (see 91av, 19 June 2004, p 32). It turns out that they are in the same place in the brains of humpback whales, fin whales, killer whales and sperm whales. What’s more, they have existed in whales for at least twice as long as we have had them, and early estimates suggest they could have three times as many as us proportionately.

“It’s absolutely clear to me that these are extremely intelligent animals,” says Patrick Hof of the Mount Sinai School of Medicine in New York, who found the whale spindle cells with colleague Estel Van Der Gucht. “We must be careful about anthropomorphic interpretation of intelligence in whales,” he adds, “but their potential for high-level brain function, clearly demonstrated already at the behavioural level, is confirmed by the existence of neuronal types once thought unique to humans and our closest relatives.”

Dolphins seem to be capable of self-recognition (91av, 4 November 2006, p 17) and Hof suspects humpback whales are too. “They communicate through huge song repertoires, recognise their own songs and make up new ones. They also form coalitions to plan hunting strategies, teach these to younger individuals, and have evolved social networks similar to those of apes and humans,” he says.

Like all other species with spindle cells, whales undergo an unusually long period of development before sexual maturity, they have very few offspring at one time, and adults can live independently from other whales for long periods.

Hof and Van Der Gucht found the spindle cells in two regions vital for “visceral” reactions – those that require fast but emotionally sensitive judgements, such as whether another individual is suffering pain and the general feel of whether an experience is pleasant or unpleasant (The Anatomical Record Part A, DOI: 10.1002/ar.a.20407).

“Whales have spindle cells in regions vital for reactions that require fast but emotionally sensitive judgements”

One area, the anterior cingulate cortex, lies beneath the midline at the front of all mammalian brains (see Diagram). In humans it guides attention, senses pain and registers mistakes. By tapping into body systems that control breathing, heart rate, erections and other automatic responses, it helps us to register emotions such as fear, disgust, anxiety and intense pleasure or pain.

The other region is the frontoinsular cortex, reckoned to be critical for emotional responses to others, such as when someone else is suffering, or a baby cries. It also helps us spot attempts at deception.

In whales, spindle cells were also found in another region, the frontopolar cortex, and were sparsely distributed elsewhere, though Hof says he doesn’t yet know the significance of spindles in these areas.

The shape of the spindle cells may provide a clue to their function. “They’re like the ‘express trains’ of the nervous system,” says Hof. Their long length enables them to fast-track information around the cortex, bypassing irrelevant connections, enabling us to instantly process and act on emotional cues during complex social interactions.

“My interpretation is that the spindles are adaptations which support fast communication of information from the anterior cingulate cortex and the frontoinsular cortex in very large brains,” says neuroscientist John Allman, a spindle cell researcher at the California Institute of Technology in Pasadena.

Spindle neurons transmit highly processed information, says Hof, which helps us formulate behavioural responses. This might include responding verbally, retrieving memories and images, empathy, feelings and insight. It’s tantalising to think that the songs and vocalisations of whales might be based on similar processing.

“The discovery is a stunning example of neuroanatomical convergence between cetaceans and primates,” says Lori Marino of Emory University in Atlanta, Georgia. “This is consistent with a growing body of evidence for parallels between cetaceans and primates in cognitive abilities, behaviour and social ecology.”

The brains of smaller cetaceans examined by Hof and Van Der Gucht didn’t have spindle cells. The only toothed whales – the suborder of cetaceans that includes dolphins – to have spindles were the two largest, the killer whale and the sperm whale. But Hof suspects that all baleen whales, such as humpbacks and fins, are likely to have the cells.

The smaller cetaceans might have evolved some kind of alternative to spindle neurons. “In this respect, it will be interesting to discover what mental capacities might distinguish humpback whales from dolphins,” says Keith Kendrick, a neuroscientist at the Babraham Institute in Cambridge, UK.

Kendrick also warns against assuming that the spindle cells must be linked with complex socialisation, which is one explanation put forward for the evolution of increased brain size. “At this point, we don’t know for sure what the key functions of these spindle cells are, and whether they really do represent an important index of higher social and intellectual functioning,” he says.

Hof is convinced, however, that the cells signify intelligence. “Whales have evolved absolutely unique traits in their environment,” he says. “They don’t have written language but they can do a lot, and their fishing strategies are better than ours.”

All the more reason, he says, for rethinking whaling strategies on humanitarian grounds. “That such a parallel trait occurs in such divergent groups of animals as primates and cetaceans speaks to the need to protect them and understand fully their biology and ecology.”