If you've ever experienced an ultrasound or studied the fetal images the technique can produce, then you may have witnessed the future of neurostimulation.
Ultrasound operates like submarine sonar systems or bats, both of which emit sound waves to sense their surroundings. The waves travel until they make contact with an object, then bounce back to the source. A bat or a computer can then determine the shape and distance of the object based on this returning sound wave.
Ultrasound imaging systems transmit high-frequency sound pulses through the human body. Every time they hit a boundary between tissues, some bounce back while others keep going. The machine then calculates the distances and frequencies involved and creates a two-dimensional image of what's going on inside the body cavity -- such as the movements of a fetus in utero.
Scientists have studied the effects of ultrasound on biological tissues since the 1920s. As early as the 1950s, researchers realized that at sufficiently high frequencies (much higher than those used in prenatal care), ultrasound also had the potential to destroy specific cells, especially tumors in the brain.
High-frequency ultrasound (HIFU) promised all of this without harming surrounding tissue or drilling a hole through a patient's skull. For decades, however, researchers lacked sufficient imaging technology to really see what was specifically happening in the brain.
Modern researchers, however, have advanced magnetic resonance imaging (MRI) to glimpse the real-time interworking of the human body. Furthermore, brain-mapping technology continues to illuminate what's going on in the human mind. To return to the equation analogy, this means knowing exactly what parts of the neural equation affect which aspects of our abilities, memory and personality.
In a recent study by neuroscientists at Arizona State University, researchers discovered that low-intensity, low-frequency ultrasound (LILFU) could apply a gentler touch. Instead of destroying cells, these lower frequencies merely stimulate brain circuit activity.