http://upgrade.io9.com/neural-dust-is-a-step-towards-nexus-806802917
Brain-computer interfaces today generally work by sticking electrodes into the brain. That runs into severe problems - all those electrodes cause trauma as they penetrate the brain, and leave wires that wind through and between the brain's neurons, potentially attracting scar tissue or driving the brain to reject the implant.
The proposed 'Neural Dust' system (and it's just a proposal for now) would work differently. The authors propose sprinkling tiny dust-sized passive silicon sensors, about 100 microns across, throughout the human cortex.'''