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Studying fish helps us gain a better understanding of human beings. How does the wealth of human emotion come about?
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Professor Yoshida heads the Biopsychology Laboratory. While involved in fisheries biology, his academic discipline is somewhat unique in that it takes a biological approach to research into the mind, which is conventionally pursued in the field of psychology.
“Although I’m studying fish, my fundamental interest is in human beings. Hoping to deepen understanding of human beings as a biological species, we work on research into fish,” says Professor Yoshida. His team use fish as their main experimental objects. To our surprise, this is because “The fish brain has the same basic structure as the human brain,” he explains.
“Needless to say, brain size is quite different between fish and human beings. It is estimated that the human brain contains 100 billion—or hundreds of billions— of neurons (nerve cells), which is well beyond our present research capacity. In contrast, the brain of, say, a goldfish - whose body length is 10 cm or so – is thought to have approximately 100 million neurons. I thought that we might manage to clarify the entire picture of the fish brain, given its small size.” |
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On the basis of this idea, Professor Yoshida first focused on “fear.”
Almost all animals feel fear, which is generally classified into emotional experience and physical reaction. “By emotional experience of fear I mean to feel fear, and by physical reaction to fear I mean the situation in which our heart beats with fear. We are not sure whether fish experience the former, since fish do not speak. However, we can investigate the latter in fish. I therefore came up with the idea that we could better understand fear in human beings by studying physical reactions of fish to fear.”
Subsequently, the Professor conducted fear-conditioning experiments to study the brain mechanisms of fear learning in goldfish. |
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Approach to fundamentals of the brain mechanisms by investigating fear: Do goldfish learn fear?
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Typical experiment procedures are as follows:
Aquariums containing goldfish are placed in a room. The goldfish are repeatedly given a slight electric shock each time the room light is turned on. If such fear-conditioning is repeated with humans, they will learn to feel fear if the light only is turn on, without the electric shock. As expected, the same holds true for goldfish: according to Professor Yoshida, they come to show a physical response to fear, if the room light alone is turned on.
As he explains, “In this experiment, we monitor fishes’ cardiac activity as a physical reaction. In the situation in which fish feel fear, their cardiac activity changes, just as with humans. However, whereas the human heart rate accelerates, the fish’s cardiac activity decelerates, sometimes even halting for ten seconds or so, because fish are weak.” |
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Weak animal species may respond in that way because such species are more likely able to survive by “freezing” (immobilizing) and remaining motionless. These responses are physical reactions that are uncontrollable for both fish and human beings alike, as the cardiac activity is regulated by the autonomic nerves. It is therefore logical to think that fish and human beings share the same brain function in this regard.
Professor Yoshida surprised us with his statement that “Our research has found that the cerebellum is deeply involved in fear learning in goldfish. Recently, our team became able to trace the progress in fear learning and the changes in cerebellar neuron activities and networks, on a real-time basis.”
What makes this research intriguing is that “We can visually observe that the fish is actually in the process of thinking,” he says. “For example, when a fish feels fear, its brain generates electricity. By recording the electricity, we can observe how fish brain activity changes. In other words, we can directly observe the brain activities, from which the movement of mind derives, on a real-time basis. We are currently the only laboratory in the world where this interesting observation is possible.” |
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A 100-year research project using hand-made experimental tools—aiming to clarify the ultimate principles of the mind by identifying all kinds of emotions
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Professor Yoshida expressed his hope of further pursuing his research not only into fear, but also various other emotions.
“Currently we are working to understand what it means to feel ‘excited’ or ‘disappointed.’ Just like us, fish may feel excited at anticipating food, or they may feel disappointed when they cannot get food. We want to study such themes.”
His team’s unique research activities have received many offers for collaboration. Expectations are growing that his team may take new approaches in collaboration with other universities and research institutes, taking advantage of their respective fields of expertise. Professor Yoshida says that their research findings may find applications in the treatment or prevention of post-traumatic stress disorder (PTSD), by helping clarify the brain mechanisms of fear. In addition, a patent is now being applied for, regarding the unique technique for measuring physical reactions, with the claim that it could help improve vehicle performance through joint research with an automobile manufacturer.
“I admit that our research will be a 100-year project. In our laboratory, we create our own experiment instruments, and even computer programs. We ourselves also catch, keep and breed fish to be used in experiments, in principle. Our policy is to overcome difficulty by exerting our originality and ingenuity,” he said with a smile.”
To achieve their goals, members of the Biopsychology Laboratory spare no effort. They can therefore experience the joy of creating something from scratch on their own, and make various discoveries in that process. The laboratory is small, enabling students to receive intensive instruction, which constitutes another attractive feature. |
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| Masayuki Yoshida |
Associate Professor
Laboratory of Fish Neurobiology
April 1, 2007 – present Associate Professor, Hiroshima University
Posted on Jul 10, 2014 |
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