By using a brain implant, people who are paralyzed.
Three people paralyzed from the neck down have been able to use unmodified computer tablets to text friends, browse the internet and stream music, thanks to an electrode array system called BrainGate2. The findings could have a major impact on the lives of those affected by neurologic disease, injury, or limb loss.
via Engadget
The system uses an array of micro-electrodes implanted into the brain which decode, in real time, the neural signals associated with the intention to move a limb. The three people involved in the trial had electrode grids implanted over part of their motor cortex — the area of the brain that helps control movement — which picked up neural activity indicating they were thinking about moving a cursor on the screen. Those patterns were then sent to a virtual mouse that was wirelessly paired to the tablet.