The real time monitoring of brain function has advanced in leaps and bounds in recent years. That's ... led to a new engineering discipline of brain-machine interfaces, which allows people to control machines by thought alone. Today, Dongjin Seo and pals at the University of California Berkeley reveal an entirely new way to study and interact with the brain. Their idea is to sprinkle electronic sensors the size of dust particles into the cortex and to interrogate them remotely using ultrasound. The ultrasound also powers this so-called neural dust. Each particle of neural dust consists of standard CMOS circuits and sensors that measure the electrical activity in neurons nearby. This is coupled to a piezoelectric material that converts ultra-high-frequency sound waves into electrical signals and vice versa. The neural dust is interrogated by another component placed beneath the scale but powered from outside the body. This generates the ultrasound that powers the neural dust and sensors that listen out for their response, rather like an RFID system. The system is also tetherless - the data is collected and stored outside the body for later analysis. [Seo and co say] implanting the neural dust particles in the cortex ... can probably be done by fabricating the dust particles on the tips of a fine wire array, held in place by surface tension, for example. This array would be dipped into the cortex where the dust particles become embedded.