Brain power

Adaptation is a way of life for Dr. Takashi Kawashima. Born in northern Japan, Dr. Kawashima had a nomadic childhood, first moving to Kobe in the west, then to Yokohama on Tokyo Bay, and eventually to Tokyo. As a neuroscientist, he has always been interested in how humans learn and adapt to their surroundings. His experience with the need to adapt to and learn about new places certainly influenced his interest in how learning happens, which grew into a research focus on how maladaptive learning can lead to addiction and psychiatric disorders.

What is learning? How does the brain acquire information? These are the questions that inspire the research of Dr. Kawashima, the first Japanese principal investigator hired by the Weizmann Institute in its history. Dr. Kawashima earned his MD and PhD from the University of Tokyo, and then went on to a postdoctoral fellowship at the Howard Hughes Medical Institute (HHMI) in Virginia. He joined the Department of Neurobiology in June.

“Learning is the conversion of transient events into persistent traits,” he says. That is, when exposed to a stimulus, brain cells initially respond with a temporary burst of activity, creating an internal representation of whatever information is present. With time and repeated exposure, this activity can eventually trigger a cascade of molecular processes that consolidate the relevance of that stimulus to life and survival. That is, the brain decides whether to categorize it as beneficial, harmful, threatening, desirable, or something else.

This categorization process is called learning, and it can happen both at the most microscopic level—changing the strength of junctions between brain cells—or alter the connective wiring between entire brain regions.

Dr. Kawashima studies an aspect of the learning process regulated by the release of a special class of chemical agents by one neuron, to change the activity of a group of other neurons, a process called neuromodulation. The chemicals involved—such as dopamine and serotonin—act as dimmers or amplifiers in the brain, much like a light switch can dim or brighten a room light, regulating the activity of a whole host of brain cells at once. He is especially interested in how dopamine and serotonin systems affect how we learn that a particular stimulus is positive or negative, and worth taking a risk to obtain or avoid. 

Addiction vs. anxiety

Refining our understanding of how our brains learn to make positive or negative associations with stimuli has major implications for understanding both addiction—when the brain learns to be excessively attracted to a stimulus—or anxiety disorders—when it is unduly repulsed. Dr. Kawashima also anticipates that his research on the action of dopamine and serotonin will have implications for understanding the relationship between the primary effects and side effects of neuropsychiatric drugs, which typically target the dopamine and serotonin systems.

One of best species to use for studying the learning process is the zebrafish, as they share many learning-related neural circuits with humans and their brains are small and transparent. This presents an exceptional opportunity to analyze and image brain function both as a whole, as well as with single-cell resolution. Fortunately—and an attraction for Dr. Kawashima—the Weizmann Institute is home to established neuroscientists and biologists who use zebrafish to study brain and vascular development. The ease of collaboration and engagement was a significant draw across the ocean.

Dr. Kawashima, who co-owns a patent related to computer vision and another related to neurogenetics. His wife, Mio Nonaka, previously a research fellow at the National Institutes of Health, is a staff scientist in the neurodevelopment lab of Prof. Orly Reiner. They have two daughters.

Their verdict on Israel so far? The hummus is great. The sushi? Not so much.

To hear a WeizmannVoices podcast with Dr. Kawashima, click here.

Dr. Kawashima is supported by the Birnbach Family Career Development Chair.