Nerves in the am­putee’s shoul­der, which once went to the am­pu­tat­ed arm, are re-rout­ed and con­nect­ed to healthy mus­cle in the chest to in­stall the device, Kuiken ex­plained. The re-rout­ed nerves grow in­to the chest mus­cle and di­rect sig­nals they once sent to the am­pu­tat­ed arm in­stead to the ro­bo­tic arm, vi­a elec­trodes.

Then, when the pa­tient thinks about mov­ing his or her arm, the ac­tion is car­ried out as it would be in a healthy arm, Kuiken said. In oth­er words, he added, the sen­sory nerves to the hand are re- rout­ed to a patch of skin on the chest. Now when Mitch­ell is touched on this skin, she feels her hand is be­ing touched.