Coming to grips with ‘monkey business’
Sandra Blakeslee, a science writer for The New York Times who specializes in the brain sciences, recently interviewed Atsushi Iriki of the RIKEN Brain Science Institute (BSI), Wako, Japan. Iriki, who helped pioneer the field of cognitive neurobiology, heads the Laboratory for Symbolic Cognitive Development and directs the Intellectual Brain Function Research Group at BSI, is an adjunct professor at Tokyo Medical and Dental University and The University of Tokyo, as well as being a visiting senior fellow of University College London and a member of the Science Council of Japan. In the interview, Iriki shares the story of the genesis of his career and his views on human evolution.
As a high school student, Atsushi Iriki wanted to understand what makes humans so different from other creatures. How did the human brain evolve its intellectual capacities? What makes Homo sapiens so exceptionally sapient?
Iriki’s first thought was that it must be language. As a bilingual speaker, he found that when he thought about something in English, and then thought about the same thing in Japanese, he would sometimes reach a different conclusion. “We think with language and we think with our brain,” he said in a recent media interview. “That made me eager to study the neuroscience of language.”
Alas, that was in 1978, long before our understandings of functional neuroanatomy could even come close to meshing with linguistic theory. Undeterred, Iriki made it his goal to help establish a new science of neurolinguistics. Reasoning that language is a function of the mouth, he decided to study dentistry. He explored tongue and tooth sensations, the anatomy of chewing, and eventually, for his postdoc at Rockefeller University in New York, how the brain’s sensory and movement systems are tightly interconnected via feedback loops.
From that unconventional beginning, Iriki went on to shed new light on the evolution of human intelligence by revealing the neural precursors of intelligent behavior in monkeys and other animals. Most notably, Japanese macaques have mental correlates for language, tool use, arithmetic, social reciprocity and other hallmarks of the human intellect.
Q:In 1990, you were back in Japan where you started what you call ‘monkey business’. What were you looking for?
A:At the time, most people studied hierarchies in the visual system—how simple visual inputs are processed and combined in different brain regions to form complex images. We were the first to look for hierarchies in the somatosensory system. How do simple touch and other sensations from the body combine to give us a sense of embodiment in space? Gradually we shifted our electrodes back [from the primary somatosensory input area] into the parietal cortex, where I found neurons involved in tool use. This led me to study the shared evolutionary components of tool use and language.
Q:Many scientists do not believe that monkeys can use tools. What led you to think you could train them?
A:It’s true that macaque monkeys rarely use tools in the wild. But Japanese macaques, compared to other monkey species, are especially good at acquiring complex cognitive and motor tasks. They are especially clever, temperamentally gentle and unusually cooperative with humans. We found neurons that become active when tools are aligned with the monkey’s hands. That is why we decided to train them to actually use tools. Their brains seemed predisposed for it. We noted they will sometimes pull down on a slender branch to eat persimmons, suggesting that latent precursors for tool use existed in their brains.
Q:How hard was it to teach tool use?
A:Very difficult. We trained them to wield handheld rakes to retrieve distant food rewards. At first it took months to train each monkey. But as we fine-tuned the protocol, we were able to train animals in 10 to 14 days. Over this time, we found that the monkeys’ brains undergo gene expression and extend physical connections by about a millimeter. Such changes bear a provocative similarity to the connectivity patterns seen in the human brain, which have been linked to our sophisticated body image—how our bodies are represented in our brains—and our ability to use tools.
Q:What does this say about evolution?
A:Although these brain changes from tool use were induced artificially, it appears that the neural-connectivity patterns in monkey brains overlap with those of humans. When people use tools, they often say it feels as if the tool has been incorporated into their body image as an extension of their hand or forearm. By examining the monkeys, we were able to show how touch and vision combine in the brain to give rise to modified body image with tool use. Thus we can use these monkeys to reveal the evolutionary pathways to human intelligence. The big step comes with increasingly sophisticated tool use. Once you can absorb tools as an extension of the self, you can disembody the self from its flesh-and-blood boundaries. Tool use becomes a precursor to the capacity to objectify the self. Similarly, once you learn to control your body and its tools, iconic and symbolic representation are poised to emerge.
Q:Can other animals use tools?
A:Yes, but not many. You need to be able to grasp objects and bring them up near the face where they can be seen and manipulated. Primates are great at this. But you can also see it in a rodent called the degu. Elephants manipulate their trunks. Crows grasp objects and bring them to their beaks. But in the human lineage, free hands with opposable thumbs led to a whole new level of tool use.
Q:So do you now have a better idea about what makes humans special?
A:As humans learned to wield ever-more sophisticated tools, they developed intentionality. They could take a third-person view and look beyond the self, through time. As they interacted with the environment, they changed and the environment changed. This is new. It led to culture and minds that operate at the abstract level, which is where language comes in.
Q:What kept monkeys from following the same path?
A:They don’t imitate. Their lives are precarious. They survive by not being curious.
Q:And what allowed humans to follow the path?
A:There were accidental combinations of elements—the tongue, mouth and motor patterns that favored language. But perhaps more important is so-called intentional niche construction, which is an extension of natural selection. In the Darwinian sense, selective pressure would favor individuals who were more adept at acquiring and mastering tools. But eventually, natural selection would no longer be determined solely by the environment. Rather, humans could decide how the environment could be made and re-made. Individual and group behavior became the prime engines for the evolutionary process. With this came metaphysical tools, like writing and mathematics. Portions of the cerebral cortex enlarged and brain circuits reorganized. The brain’s basic capacity to reorganize, to be plastic, was further enhanced by tool use.
Q:Is this process still ongoing?
A:Absolutely. With the melding of minds and machines, we may see the emergence of a new kind of intelligence. We may soon have ‘multiselves’ thriving in cyberspace.
Intellectual Brain Function Research Group
Using behavioral and neurophysiological studies of macaque monkeys, which have been trained to use tools and other high-tech equipment, Atsushi Iriki and his colleagues are currently working to uncover evolutionary precursors of human higher cognitive functions that have a basis in physical morphologies and patterns of structured bodily actions. The aim of this work is to understand the neural mechanisms of social behaviors. His group is also striving to reveal developmental clues of symbolic cognitive functions that characterize human intelligence.
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