Brain Physiology
- Why does the world not move when we move our eyes?
- The brain science of mental time
- How does the brain optimize goal-directed movements?
- Why do we blink? （Associate Prof. Tamami Nakano）
The lab aims to study how “Kokoro” or the mind emerges from the brain by solving research questions that we can experience.
Why does the world not move when we move our eyes?
Our eyes move 3 times a second, yet our perception does not see a moving world. How our brain interprets our environment this way is a fundamental problem that had been questioned for centuries by great philosophers like Descartes. We have hypothesized that the brain stabilizes the visual world using the background scenery as the reference. Studies to test this hypothesis have examined 1) human behavior, 2) human brain activity, 3) monkey neural activity, and 4) activity of artificial neural circuits.
Figure 1 We identified a neural correlate of the background coordinate in the right precuneus [1]
2. The brain science of mental time
We have a sense of time in that we are conscious of the present, past, and future. However, there is no receptor of “time” anywhere in our body. This is a mystery because there are photoreceptors for vision in the eyes or mechanoreceptors for sense of touch on the skin. To find how the brain constructs “time”, we studied how the brain orders two sequential events and have discovered that subjective temporal order is reconstructed by combining information on motion and position in the brain [2, 3]. In 2013, we launched a joint research project, “The Science of Mental Time” supported by Grant-in-Aid for Scientific Research on Innovative areas, which includes over 30 research groups.
3. How does the brain optimize goal-directed movements?
When we reach for something with our hands, our brain is able to calculate the necessary movement that minimizes the variance of error subconsciously. The brain is able to make all the necessary computations in a blink of an eye. We discovered that the error information necessary for this optimization is conveyed to the cerebellum by the climbing fibers [4]. More recently, we showed that the learning based on the error signal can be manipulated by electrical stimulation to the motor and premotor cortices [5].
Figure 2 Signals that optimize reaching pass through the motor cortices [5]
4. Why do we blink? (Associate Professor Tamami Nakano)
People blink spontaneously about once every 3 seconds. Noting that blinking serves to moisten the eyes and that one blink every 20 seconds would be enough, the purpose of this frequent blinking has remained a mystery. We examined brain activity as well as timing of blinking while participants were observing a video clip or engaged in face-to-face conversation. We eventually found that we share timing of blinking, at a conclusion of a flow of information, and that each blink triggers a transient but dynamic change of activity in the major neural networks [6]. These findings have been recognized by both domestic and international media, and the research was selected as a PRESTO project in 2016.
References
1. Uchimura et al., Eur J Neurosci 42 (1): 1651-1659, 2015.
2. Yamamoto and Kitazawa, Nat Neurosci 4 (7): 759-765, 2001.
3. Takahashi and Kitazawa, J Neurosci (in press).
4. Kitazawa et al., Nature 392 (6675): 494-7, 1998.
5. Inoue et al., Neuron 90 (5): 1114-26, 2016
6. Nakano et al., PNAS 110 (2): 702-6, 2013.
