If my attentive reader clicked on the link leading to this article because they recognized this famous piece of art, drawn in 19th century Japan, or were intrigued by my article’s unusual title, there might be a deep subconscious reason for that. And it is not just for the popularity of “The Great Wave of Kanagawa” that it gained in mass culture as the first of its kind piece of art combining traditional Japanese and European blueprint techniques. Nor because it is often used as a decor in fashionable coffee houses or high cuisine restaurants. Nor because of its ability to elicit flashbacks of horror and trepidation in mass consciousness associated with recent natural disasters all over the world. It’s because brain tsunamis are a phenomenon that many have experienced personally without realizing.
Spreading depolarizations, often called brain tsunamis, are waves of unusual electrical activity that ripple outward from the site of origin in the brain. It is a chain reaction involving a change in the normal activity of neurons that is passed along to the next cell and so on and so forth. As this unusual pattern of activity propagates, it causes a change in how much oxygen the nearby vessels can carry and causes the nearby supporting cells to release dozens of various signaling substances that may have mixed effects on the brain. Spreading depolarizations (for brevity called SDs) can occur in virtually all multicellular animals that have some kind of nervous system, ranging from the simplest prehistoric underwater creatures to their insect relatives, to vertebrates, including rodents, cats, dogs, monkeys, and us humans. SDs can occur spontaneously (without an apparent cause) or in certain disease conditions, but what exactly triggered them is poorly understood.
Because SDs are widespread and prevalent in the animal kingdom, some scientists argue that they may serve a well-conserved evolutionary purpose as a protection mechanism that safeguards the brain from stress and an excess energy consumption in critical situations, such as after physical trauma, or sleep deprivation, or strenuous brain stimulation by the external events. Likely, most people experience SDs at some point in their lives, manifested as dizziness, spreading distortion of sensations, including skin crawls, blurry vision or altered audition.
The problem is that SDs are often cited as strong indicators of poor outcomes in patients with acquired brain injury. Research groups in the New Mexico School of Medicine, Charite Clinic Berlin, Harvard, Pittsburgh University, Dalhousie University and many more, independently and in collaboration with each other, are coming to the same conclusion. By poor outcome, the experts in the field are often referring to long-term disability, including inability to walk or speak, delayed epilepsy, mood disorders and even sudden death. In fact, the link between SDs and poor brain injury outcome is so strong that much research effort is focused on understanding whether SDs are a mere marker of injury or underly additional “secondary” injury beyond what was rendered to the brain by the initial trauma or disease. The traumatic brain injury, akin to an earthquake shaking the bottom of the ocean, could provoke SDs that then cause additional harm, akin to tsunamis that reach the seashore and cause harm that would not result from a distant earthquake itself.
Understanding SDs is, therefore, important for identifying patients at risk of further damage. It is also important to study the SDs that can be protective and those that can do harm. Complex brain activity patterns are elusive, can be fascinating, but also damaging. Just like ocean waves, they can be harmonious, powerful, or devastating. This is what inspired the nickname of SDs, “the brain tsunami,” resonating with why “The Great Wave of Kanagawa” has gained popularity. A tsunami, distant in the ocean, is a beautiful natural phenomenon, capturing the attention of the master Hokusai, who, like scientists in the lab, studied the anatomy of the waves and water forms to be captured on canvas. The same tsunami that injures and takes away vulnerable lives, just as SDs do.
Photo by Katsushika Hokusai via Metropolitan Art Museum
