DARPA break­throughs in pros­thet­ics and neu­ral in­ter­faces


To un­der­stand the mean­ing of “pro­pri­o­cep­tion,” try a sim­ple ex­per­i­ment. Close your eyes and lift your right arm above your head. Then, move it down so that it’s par­al­lel to the ground. Make a fist and re­lease it. Move it for­ward, and then swing it around be­hind you like you’re stretch­ing. Fi­nally, freeze in place, open your eyes, and look. Is your arm po­si­tioned where you thought it would be?

For most people, the an­swer will be, “Yes.” That’s be­cause your brain and ner­vous sys­tem worked to­gether to move your body ac­cord­ing to your in­tent and pro­cessed the sen­sory feed­back to know where your arm was in space de­spite not be­ing able to vis­ually track it.

For many up­per-limb am­putees us­ing pros­thetic de­vices, the an­swer would be, “No.” They wouldn’t have con­fi­dence that their de­vice would be where they think it is be­cause cur­rent pros­the­ses lack pro­vi­sions for pro­vid­ing com­plex tac­tile and pro­pri­o­cep­tive feed­back to the user. With­out this feed­back, even the most ad­vanced pros­thetic limbs will re­main numb to the user and ma­nip­u­la­tion func­tions will be im­paired.

The De­fense Ad­vanced Re­search Projects Agency’s (DARPA) new hand pro­pri­o­cep­tion and touch in­ter­faces (HAPTIX) pro­gramme seeks to deliver those kinds of nat­u­ral­is­tic sen­sa­tions to am­putees, and in the process, en­able in­tu­itive, dex­ter­ous con­trol of ad­vanced pros­thetic de­vices that sub­sti­tute for am­pu­tated limbs, pro­vide the psy­cho­log­i­cal ben­e­fit of im­prov­ing pros­the­sis “em­bod­i­ment,” and re­duce phan­tom limb pain. The pro­gramme builds on neu­ral-in­ter­face tech­nolo­gies ad­vanced dur­ing DARPA’s Revo­lu­tion­is­ing Pros­thet­ics and Re­li­able Neu­ral-In­ter­face Tech­nol­ogy (RENET) pro­grammes that made ma­jor steps for­ward in pro­vid­ing a di­rect and pow­er­ful link be­tween user in­tent and pros­the­sis con­trol.

HAPTIX aims to achieve its goals by de­vel­op­ing in­ter­face sys­tems that mea­sure and de­code mo­tor sig­nals recorded in pe­riph­eral nerves and/or mus­cles. The pro­gramme will adapt one of the ad­vanced pros­thetic limb sys­tems de­vel­oped un­der Revo­lu­tion­is­ing Pros­thet­ics to in­cor­po­rate sen­sors that pro­vide tac­tile and pro­pri­o­cep­tive feed­back to the user, de­liv­ered through pat­terned stim­u­la­tion of sen­sory path­ways in the pe­riph­eral nerve. One of the key chal­lenges will be to iden­tify stim­u­la­tion pat­tern­ing strate­gies that elicit nat­u­ral­is­tic sen­sa­tions of touch and move­ment. The ul­ti­mate goal is to cre­ate a fully-im­plantable de­vice that is safe, re­li­able, ef­fec­tive, and ap­proved for hu­man use.

“Pe­riph­eral nerves are in­for­ma­tion-rich and read­ily ac­ces­si­ble tar­gets for in­ter­fac­ing with the hu­man ner­vous sys­tem. Re­search per­formed un­der DARPA’s RE-NET pro­gramme and else­where showed that these nerves main­tain mo­tor and sen­sory fi­bres that pre­vi­ously in­ner­vated the am­pu­tated limb, and that these fi­bres re­main func­tional for decades af­ter limb loss,” said Doug We­ber, the DARPA Pro­gram Man­ager. “HAPTIX will try to tap in to these bi­o­log­i­cal com­mu­ni­ca­tion path­ways so that users can con­trol and sense the pros­the­sis via the same neu­ral sig­nal­ing path­ways used for in­tact hands and arms.”

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