title: Feedback control policies employed by people using intracortical brain-computer interfaces.
abstract: When using an intracortical BCI (iBCI), users modulate their neural population activity to move an effector towards a target, stop accurately, and correct for movement errors. We call the rules that govern this modulation a 'feedback control policy'. A better understanding of these policies may inform the design of higher-performing neural decoders.
  
  
  
  We studied how three participants in the BrainGate2 pilot clinical trial used an iBCI to control a cursor in a 2D target acquisition task. Participants used a velocity decoder with exponential smoothing dynamics. Through offline analyses, we characterized the users' feedback control policies by modeling their neural activity as a function of cursor state and target position. We also tested whether users could adapt their policy to different decoder dynamics by varying the gain (speed scaling) and temporal smoothing parameters of the iBCI.
  
  
  
  We demonstrate that control policy assumptions made in previous studies do not fully describe the policies of our participants. To account for these discrepancies, we propose a new model that captures (1) how the user's neural population activity gradually declines as the cursor approaches the target from afar, then decreases more sharply as the cursor comes into contact with the target, (2) how the user makes constant feedback corrections even when the cursor is on top of the target, and (3) how the user actively accounts for the cursor's current velocity to avoid overshooting the target. Further, we show that users can adapt their control policy to decoder dynamics by attenuating neural modulation when the cursor gain is high and by damping the cursor velocity more strongly when the smoothing dynamics are high.
  
  
  
  Our control policy model may help to build better decoders, understand how neural activity varies during active iBCI control, and produce better simulations of closed-loop iBCI movements.
authors.affiliation: Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA.|Louis Stokes Cleveland Department of Veterans Affairs Medical Center, FES Center of Excellence, Rehab. R&D Service, Cleveland, OH, USA.
authors.forename: Francis R
authors.initials: FR
authors.lastname: Willett
authors.affiliation: Department of Neurosurgery, Stanford University, Stanford, CA, USA.|Department of Electrical Engineering, Stanford University, Stanford, CA, USA.|Stanford Neurosciences Institute, Stanford University, Stanford, CA, USA.
authors.forename: Chethan
authors.initials: C
authors.lastname: Pandarinath
authors.affiliation: Department of Neuroscience, Brown University, Providence, RI, USA.|Center for Neurorestoration and Neurotechnology, Rehabilitation R&D Service, Department of Veterans Affairs Medical Center, Providence, RI, USA.|Brown Institute for Brain Science, Brown University, Providence, RI, USA.
authors.forename: Beata
authors.initials: B
authors.lastname: Jarosiewicz
authors.affiliation: Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA.|Louis Stokes Cleveland Department of Veterans Affairs Medical Center, FES Center of Excellence, Rehab. R&D Service, Cleveland, OH, USA.
authors.forename: Brian A
authors.initials: BA
authors.lastname: Murphy
authors.affiliation: Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA.|Louis Stokes Cleveland Department of Veterans Affairs Medical Center, FES Center of Excellence, Rehab. R&D Service, Cleveland, OH, USA.
authors.forename: William D
authors.initials: WD
authors.lastname: Memberg
authors.affiliation: Department of Neurosurgery, Stanford University, Stanford, CA, USA.
authors.forename: Christine H
authors.initials: CH
authors.lastname: Blabe
authors.affiliation: Center for Neurorestoration and Neurotechnology, Rehabilitation R&D Service, Department of Veterans Affairs Medical Center, Providence, RI, USA.|School of Engineering, Brown University, Providence, RI, USA.
authors.forename: Jad
authors.initials: J
authors.lastname: Saab
authors.affiliation: Louis Stokes Cleveland Department of Veterans Affairs Medical Center, FES Center of Excellence, Rehab. R&D Service, Cleveland, OH, USA.|Department of Neurology, University Hospitals Case Medical Center, Cleveland, OH, USA.
authors.forename: Benjamin L
authors.initials: BL
authors.lastname: Walter
authors.affiliation: Louis Stokes Cleveland Department of Veterans Affairs Medical Center, FES Center of Excellence, Rehab. R&D Service, Cleveland, OH, USA.|Department of Neurosurgery, University Hospitals Case Medical Center, Cleveland, OH, USA.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Sweet
authors.affiliation: Louis Stokes Cleveland Department of Veterans Affairs Medical Center, FES Center of Excellence, Rehab. R&D Service, Cleveland, OH, USA.|Department of Neurosurgery, University Hospitals Case Medical Center, Cleveland, OH, USA.
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Miller
authors.affiliation: Department of Neurosurgery, Stanford University, Stanford, CA, USA.|Stanford Neurosciences Institute, Stanford University, Stanford, CA, USA.
authors.forename: Jaimie M
authors.initials: JM
authors.lastname: Henderson
authors.affiliation: Department of Electrical Engineering, Stanford University, Stanford, CA, USA.|Stanford Neurosciences Institute, Stanford University, Stanford, CA, USA.|Department of Neurobiology, Stanford University, Stanford, CA, USA.|Department of Bioengineering, Stanford University, Stanford, CA, USA.|Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA.
authors.forename: Krishna V
authors.initials: KV
authors.lastname: Shenoy
authors.affiliation: Center for Neurorestoration and Neurotechnology, Rehabilitation R&D Service, Department of Veterans Affairs Medical Center, Providence, RI, USA.|Brown Institute for Brain Science, Brown University, Providence, RI, USA.|School of Engineering, Brown University, Providence, RI, USA.|Department of Neurology, Massachusetts General Hospital, Boston, MA, USA.
authors.forename: John D
authors.initials: JD
authors.lastname: Simeral
authors.affiliation: Center for Neurorestoration and Neurotechnology, Rehabilitation R&D Service, Department of Veterans Affairs Medical Center, Providence, RI, USA.|Brown Institute for Brain Science, Brown University, Providence, RI, USA.|School of Engineering, Brown University, Providence, RI, USA.|Department of Neurology, Massachusetts General Hospital, Boston, MA, USA.|Department of Neurology, Harvard Medical School, Boston, MA, USA.
authors.forename: Leigh R
authors.initials: LR
authors.lastname: Hochberg
authors.affiliation: Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA.|Louis Stokes Cleveland Department of Veterans Affairs Medical Center, FES Center of Excellence, Rehab. R&D Service, Cleveland, OH, USA.
authors.forename: Robert F
authors.initials: RF
authors.lastname: Kirsch
authors.affiliation: Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH, USA.|Louis Stokes Cleveland Department of Veterans Affairs Medical Center, FES Center of Excellence, Rehab. R&D Service, Cleveland, OH, USA.
authors.forename: A Bolu
authors.initials: AB
authors.lastname: Ajiboye
mesh_terms: D001676:Biofeedback, Psychology / Q000379:methods / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D003198:Computer Simulation; D019054:Evoked Potentials, Motor / Q000502:physiology; D025461:Feedback, Physiological / Q000502:physiology*; D005260:Female; D006801:Humans; D007092:Imagination / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D009068:Movement / Q000502:physiology*; D010865:Pilot Projects; D013647:Task Performance and Analysis