Abstract: A three-layer brain-computer interface system includes at least one external device, a plurality of second devices implanted on the surface of the cortex of a subject's brain and a plurality of micro devices implanted deeper within the brain. The external device provides power to the second devices and receives data from the second devices. The second devices include data and power receiving/transmission means and sensors, such as for electrocorticography, and provide power and data to the micro devices, such as ultrasound data and power transmission. The micro devices include sensor means and micro LEDS for measuring electric, chemical or other brain signals and provide brain stimulus through micro LEDs or other stimulating means, such as electric or chemical stimulation. The micro devices also receive and transmit data to and from the second devices. The system provides an energy efficient wireless measuring and stimulus system for implantation in the brain tissue.