title: Ten-dimensional anthropomorphic arm control in a human brain-machine interface: difficulties, solutions, and limitations.
abstract: OBJECTIVE
  In a previous study we demonstrated continuous translation, orientation and one-dimensional grasping control of a prosthetic limb (seven degrees of freedom) by a human subject with tetraplegia using a brain-machine interface (BMI). The current study, in the same subject, immediately followed the previous work and expanded the scope of the control signal by also extracting hand-shape commands from the two 96-channel intracortical electrode arrays implanted in the subject's left motor cortex.
  
  
  METHODS
  Four new control signals, dictating prosthetic hand shape, replaced the one-dimensional grasping in the previous study, allowing the subject to control the prosthetic limb with ten degrees of freedom (three-dimensional (3D) translation, 3D orientation, four-dimensional hand shaping) simultaneously.
  
  
  RESULTS
  Robust neural tuning to hand shaping was found, leading to ten-dimensional (10D) performance well above chance levels in all tests. Neural unit preferred directions were broadly distributed through the 10D space, with the majority of units significantly tuned to all ten dimensions, instead of being restricted to isolated domains (e.g. translation, orientation or hand shape). The addition of hand shaping emphasized object-interaction behavior. A fundamental component of BMIs is the calibration used to associate neural activity to intended movement. We found that the presence of an object during calibration enhanced successful shaping of the prosthetic hand as it closed around the object during grasping.
  
  
  CONCLUSIONS
  Our results show that individual motor cortical neurons encode many parameters of movement, that object interaction is an important factor when extracting these signals, and that high-dimensional operation of prosthetic devices can be achieved with simple decoding algorithms. ClinicalTrials.gov Identifier: NCT01364480.
authors.affiliation: Department of Physical Medicine and Rehabilitation, University of Pittsburgh, Pittsburgh, PA, USA. Center for the Neural Basis of Cognition, Pittsburgh, PA, USA.
authors.forename: B
authors.initials: B
authors.lastname: Wodlinger
authors.forename: J E
authors.initials: JE
authors.lastname: Downey
authors.forename: E C
authors.initials: EC
authors.lastname: Tyler-Kabara
authors.forename: A B
authors.initials: AB
authors.lastname: Schwartz
authors.forename: M L
authors.initials: ML
authors.lastname: Boninger
authors.forename: J L
authors.initials: JL
authors.lastname: Collinger
mesh_terms: D000328:Adult; D001132:Arm / Q000503:physiopathology*; D001186:Artificial Limbs; D062207:Brain-Computer Interfaces; D003198:Computer Simulation; D004569:Electroencephalography / Q000379:methods; D019544:Equipment Failure Analysis; D019054:Evoked Potentials, Motor; D025461:Feedback, Physiological; D005260:Female; D006801:Humans; D007092:Imagination; D007596:Joints / Q000503:physiopathology*; D008954:Models, Biological; D011474:Prosthesis Design; D011782:Quadriplegia / Q000503:physiopathology* / Q000534:rehabilitation; D012371:Robotics / Q000295:instrumentation*