Atsushi Iriki
Laboratory Head
Laboratory for Symbolic Cognitive Development
Intellectual Brain Function Research Group
Brain Science Institute
“The most important feature of human beings seems to be their ‘obscureness’,” says Atsushi Iriki, team leader in the Laboratory for Symbolic Cognitive Development at the Intellectual Brain Function Research Group in the RIKEN Brain Science Institute. While we converse, we cannot know what our partner is thinking. However, I can proceed with the conversation for the present, assuming that my partner is ‘identical to myself’. “I think that the ‘concept’ that others are identical to ourselves and accepting this ‘obscureness’ and ‘vagueness’ are the origins of human intelligence.” How, then, did human intelligence emerge? Iriki attributes this process to the use of tools. Accumulating data has demonstrated that Japanese macaques and degus, the latter a kind of rodent, are capable of using tools after training. Changes in brain functioning that may have led to human intelligence are being elucidated.
Japanese macaque and degu.
Iriki has shown that Japanese macaques and degus (rodents) can be trained to use tools. It is thought that the brain mechanism for higher functions such as tool use is essentially present not only in humans and some other primates but also in other animals. As such, Japanese macaques and degus seem to become able to use tools after training, making good use of their facile paws as hands to handle tools and highly functional eyes. A thumb-like projection is present in the degu’s paw, allowing it to grip a thin rod or similar implement.
Knowing what a human being is
Iriki asks, “What is a human being? What makes a human being as he is? I wanted to answer these questions.” This is what motivated Iriki to become a scientist. “After thinking about the problem in various ways, I came up with the notion that ‘language’ makes human beings as they are, and I began to want to know the brain mechanism behind language.” However, this was still in the second half of the 1970s. It was not until much later that language became the subject of brain science. To study language scientifically, Iriki chose the department of dentistry at university. “This was because speaking is done with the mouth. Although everyone laughed at me, my choice was the result of my careful consideration.”
Now, after more than 20 years, Iriki is head of the Laboratory for Symbolic Cognitive Development at the Brain Science Institute (BSI). When visiting the Laboratory’s home page, one can see a winking elephant on the screen. “This is a joke, because the kanji character denoting an elephant also means ‘symbolic,’ but it is difficult to explain the joke to foreigners,” says Iriki with a laugh, explaining the concept behind the research at his laboratory. “When thinking of something abstract, human beings create a wide variety of concepts. Although there are no significant differences in basic design between human and primate brains, their abilities differ widely. We are working to explain how the basis for the higher functions of the brain that allow concept formation has developed through the process of evolution from monkeys to humans.”
Major subjects studied at the department of dentistry were the prevention, diagnosis, and treatment of oral disease. These seem to be unrelated to language; how did Iriki view the situation? “The only thing you can do is to do your best in the situation you have chosen. Diligent work will bring you to a next turning point. Then you can naturally choose the way that leads to what you want to do.” He studied oral sensation in the department of dentistry, and oral motion as a graduate student. Sucking behavior in babies is instinctive, but mastication requires learning. Iriki proceeded to study the mechanism behind mastication-related motor learning in the mouth.
Then, in 1987, Iriki had the opportunity to study in the US at the Rockefeller University, where he was engaged in research into the mechanism of motion learning in the hand, and made a major discovery. “Motion learning in the hand requires signaling from the somatosensory field, which is responsible for processing information on the tactile sense, and I discovered through my study with cats that there is ‘long-term potentiation’ in the motor field,” says Iriki. Long-term potentiation is a phenomenon in which repeated stimulation of a particular neuron results in enhancement of the signaling efficiency of the synapse that transmits information to the adjacent neuron. Until then, long-term potentiation had been considered unique to the visual field and the hippocampus, which controls memory, where the phenomenon was first discovered. “Now long-term potentiation is found in many areas of the brain, but my discovery was not accepted by those who stated that this phenomenon should not exist in the motor field,” says Iriki in retrospect. “The somatosensory field is important to motor learning in the hand. Then, after I returned to Japan, I began an extensive study of the somatosensory field with the use of monkeys.”
In fact, Iriki had another reason for focusing on the somatosensory field. “Many scientists in the world are studying the visual field. The functions of the visual field can be investigated simply by showing images on a screen to a subject monkey in another room. By contrast, however, if the functions of the somatosensory field are to be examined, the researcher must stay in the same room as the monkey and touch its body directly. This can quite painful because the researcher unavoidably gets scratches and bruises. So, only about ten groups in the world were studying the somatosensory field. I think that was lucky for me.”
Japanese macaques wield tools
In January 1993 Iriki encountered a major turning point. While on vacation in Okinawa, Iriki was playing roulette with his family at a casino-like facility in their hotel. The croupier was using a rake to move the heaps of chips stacked on the table. At that moment, an idea hit Iriki—I will train monkeys to use a rake to reach out and get their favorite food. It might be possible to find the change that leads to the development of human brain functions by examining the brain functions of monkeys as they learn to wield tools.
“However,” he says, “ as occurred with long-term potentiation, I met strong criticism from people who said that Japanese macaques cannot use tools at all. But I believed in my intuition.”
Iriki began to train Japanese macaques to use a rake to get their favorite food placed just out of their reach. Although they were initially unable to do the task, they learned to do it after several months of training. Examination of neural activity revealed an interesting fact. The mode of the neural activity in a portion of the cerebrum known as the parietal association area changed after the training in tool use. “In the parietal association area, there are neurons that compare somatic sensation with visual information and become activated upon recognizing the body. In untrained monkeys, these neurons do not become activated because the rake is nothing more than a foreign implement. After they become able to use the rake as a tool as a result of training, however, the neurons become active as if the rake is recognized as an extension of the hand” (Fig. 1).
Iriki continues, “When examining the neural activity, I realized that the most natural way of interpreting the Japanese macaques’ action was that they recognized the rake as an extension of their body, although in reality it is not.” While using a tool, you feel as if it is an extension of your body. This feeling explains the findings.
This achievement attracted great attention because it demonstrated that the Japanese macaque, which seldom uses tools in nature, is capable of exhibiting the higher function of being trained to use a tool, and that its brain functioning changes after training.
Degus, rodents capable of recognizing and using tools
Iriki joined the BSI in 2004. “In recent years, research budgets are more likely to be available for applied research projects that are expected to produce results in the short term and become immediately useful in our lives. Even so, the BSI allows us to conduct research that may not lead directly to applications but is really meaningful and eventually useful. What is a human being? Research into this theme cannot be carried out anywhere else.”
In March 2008 Iriki published a press release on the achievements of his joint work with Kazuo Okanoya, team leader in the Laboratory for Biolinguistics at the BSI. On the following day, newspapers had headlines such as “Rodents can use tools, get food using rake” (Chugoku Shimbun) and “Rodents use a tool! Get food using a rake” (Mainichi Shimbun). “The point of note in our achievement was the fact that we succeeded in training degus, a kind of rodent, to understand the function of a tool. Our achievement was also featured by overseas media in general publications including the New York Times and Scientific American.”
The degu is a rodent measuring about 12 cm in length and weighing about 200 g, which lives in the Andean mountains. Why did Iriki use this small animal for his experiments? “Because it was there,” answers Iriki with a laugh. Okanoya and his colleagues were keeping degus with the expectation that they might serve as experimental material for research into the evolution of language: they communicate with members of their group by singing in different voices, which gave the animal the nickname ‘singing rodent.’ Degus are also dexterous at putting containers of different sizes on top of each other. Iriki was familiar with this behavior of degus, and a new idea flashed into his mind: “Surely degus can use tools!”
As with Japanese macaques, Iriki first trained degus to get food by simply pulling in a rake in front of which food was placed (Fig. 2). They became able to do this task after about a week. Later, they learned the more sophisticated skill of pushing the rake out to gather the food, and then pulling it in. Furthermore, when a rake without teeth and an intact counterpart were placed side by side, the degus chose the useful one. These findings demonstrate that degus recognized the rake as a tool for getting food that was out of their reach, and that they are capable of choosing something functional by deducing its function from its appearance.
No special brain function required for tool use
Although it has long been thought that rodents cannot use tools, the degus trained in Iriki’s experiments were able to use the rake. He explains, “Unexpectedly, degus have facile paws to interact with the outer world and highly functional eyes to confirm the results of their actions; this is a hallmark of intelligent primates. Given the essential function of the brain for processing information from the eyes and hands, it allows the use of tools. The higher function of using tools had been thought to rely on the special brain function found in humans and some other primates only. However, the reality is different. The brain mechanism responsible for the higher functions, including tool use, is essentially present not only in monkeys but also in rodents. In my experiments, these animals became able to exploit the function as a result of training.” The laboratory training may present some clues to the process of natural evolution from monkeys to human beings.
The present achievement marked a major step toward understanding the human brain. “It is difficult to apply molecular biological techniques to studying monkeys. We have needed an experimental system that would enable us to use this kind of approach with mice for experimental work in the life sciences.” The Laboratory for Symbolic Cognitive Development has already instituted an analytical study at the molecular level to explore changes in the modes of gene functioning and neural activity seen in degus before and after learning how to use tools.
Emergence of mind and language
Iriki thinks that the functional changes in the brain occured with the use of tools produce the mind. The act of using a tool can be described as the handling of the tool, an object, by the body, the subject. As described in the example of the Japanese macaques, a tool is recognized as an extension of the body, the subject, during use. At the same time, this means that, just like the tool, the body is also seen as an object. Inevitably, the user of the tool comes to assume that there is a subject that acts on both the body and the tool as objects. This is the mind.
Another interesting finding in the experiments with Japanese macaques is that their chattering changed between when they wanted food and when they wanted a rake to reach out to get it. “It implies that there is a link between the use of tools and language,” says Iriki. “I think that the use of tools and language have evolved in parallel. There are many common elements in using tools and language, including the operation of symbolic cognition and control of complicated movements. I want to explore how language has emerged and evolved in association with functional changes in the brain due to the use of tools. After more than 20 years of research, I have just returned to my starting point.”
Some neurons become active when we perform an action, and also become active when we see someone else doing the same action. As such, mirror neurons are involved in a wide variety of brain functions, and Iriki thinks that this characteristic of mirror neurons can explain the origins of the human intellect, including the formation of views of the world and cultures and civilizations, and the features and structure of how we think and feel, in addition to the frequently mentioned birth and evolution of the mind and language. “In the near future, we will be able to clarify the nature of the mind, language, and even intellect, emotion, and volition, at the neural and molecular levels.”
What are human beings? Is this question about to be answered? “No, it will take much longer to find the answer. All I can do is to solve the problems one by one. Because truth resides in nature, we must approach nature in a modest way.” Iriki keeps in mind the proverb ‘Study nature, not book,’ which his grandfather, a biologist, told him. “It’s my hope to leave my name to posterity in a unit of measure, a scientific law or something similar. I want to revise the conventional view of science and start a new era,” says the inquisitive Iriki confidently.
About the researcher
Atsushi Iriki was born in Tokyo in 1957. He holds doctorates in dentistry and medicine. He completed his Ph.D. course at the Tokyo Medical and Dental University. He served as a Research Associate at the Rockefeller University, as an Assistant Professor in the Department of Physiology at the Toho University School of Medicine, and as a Professor in the Section of Cognitive Neurobiology at Tokyo Medical and Dental University Graduate School; he has been in his current position since 2004, specializing in neurophysiology.
