title: Non-causal spike filtering improves decoding of movement intention for intracortical BCIs.
abstract: BACKGROUND
  Multiple types of neural signals are available for controlling assistive devices through brain-computer interfaces (BCIs). Intracortically recorded spiking neural signals are attractive for BCIs because they can in principle provide greater fidelity of encoded information compared to electrocorticographic (ECoG) signals and electroencephalograms (EEGs). Recent reports show that the information content of these spiking neural signals can be reliably extracted simply by causally band-pass filtering the recorded extracellular voltage signals and then applying a spike detection threshold, without relying on "sorting" action potentials.
  
  
  METHODS
  We show that replacing the causal filter with an equivalent non-causal filter increases the information content extracted from the extracellular spiking signal and improves decoding of intended movement direction. This method can be used for real-time BCI applications by using a 4ms lag between recording and filtering neural signals.
  
  
  RESULTS
  Across 18 sessions from two people with tetraplegia enrolled in the BrainGate2 pilot clinical trial, we found that threshold crossing events extracted using this non-causal filtering method were significantly more informative of each participant's intended cursor kinematics compared to threshold crossing events derived from causally filtered signals. This new method decreased the mean angular error between the intended and decoded cursor direction by 9.7° for participant S3, who was implanted 5.4 years prior to this study, and by 3.5° for participant T2, who was implanted 3 months prior to this study.
  
  
  CONCLUSIONS
  Non-causally filtering neural signals prior to extracting threshold crossing events may be a simple yet effective way to condition intracortically recorded neural activity for direct control of external devices through BCIs.
authors.affiliation: Department of Neuroscience, Brown University, Providence, RI, USA; Brown Institute for Brain Science, Brown University, Providence, RI, USA. Electronic address: masse@uchicago.edu.
authors.forename: Nicolas Y
authors.initials: NY
authors.lastname: Masse
authors.affiliation: Department of Neuroscience, Brown University, Providence, RI, USA; Brown Institute for Brain Science, Brown University, Providence, RI, USA; Center for Neurorestoration and Neurotechnology, Rehabilitation R&D Service, Department of Veterans Affairs Medical Center, Providence, RI, USA.
authors.forename: Beata
authors.initials: B
authors.lastname: Jarosiewicz
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; Brown Institute for Brain Science, Brown University, Providence, RI, USA.
authors.forename: John D
authors.initials: JD
authors.lastname: Simeral
authors.affiliation: School of Engineering, Brown University, Providence, RI, USA; Brown Institute for Brain Science, Brown University, Providence, RI, USA.
authors.forename: Daniel
authors.initials: D
authors.lastname: Bacher
authors.affiliation: School of Engineering, Brown University, Providence, RI, USA.
authors.forename: Sergey D
authors.initials: SD
authors.lastname: Stavisky
authors.affiliation: Neurology, Massachusetts General Hospital, Boston, MA, USA; Harvard Medical School, Boston, MA, USA.
authors.forename: Sydney S
authors.initials: SS
authors.lastname: Cash
authors.affiliation: Neurology, Massachusetts General Hospital, Boston, MA, USA.
authors.forename: Erin M
authors.initials: EM
authors.lastname: Oakley
authors.affiliation: Neurology, Massachusetts General Hospital, Boston, MA, USA.
authors.forename: Etsub
authors.initials: E
authors.lastname: Berhanu
authors.affiliation: Neurosurgery, Massachusetts General Hospital, Boston, MA, USA; Harvard Medical School, Boston, MA, USA.
authors.forename: Emad
authors.initials: E
authors.lastname: Eskandar
authors.affiliation: Neurosurgery, Massachusetts General Hospital, Boston, MA, USA.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Friehs
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; Brown Institute for Brain Science, Brown University, Providence, RI, USA; Neurology, Massachusetts General Hospital, Boston, MA, USA; Harvard Medical School, Boston, MA, USA.
authors.forename: Leigh R
authors.initials: LR
authors.lastname: Hochberg
authors.affiliation: Center for Neurorestoration and Neurotechnology, Rehabilitation R&D Service, Department of Veterans Affairs Medical Center, Providence, RI, USA; Department of Neuroscience, Brown University, Providence, RI, USA; Brown Institute for Brain Science, Brown University, Providence, RI, USA.
authors.forename: John P
authors.initials: JP
authors.lastname: Donoghue
mesh_terms: D000200:Action Potentials; D000368:Aged; D001696:Biomechanical Phenomena; D001921:Brain / Q000503:physiopathology*; D062207:Brain-Computer Interfaces; D004567:Electrodes, Implanted; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D009483:Neuropsychological Tests; D010865:Pilot Projects; D011782:Quadriplegia / Q000503:physiopathology / Q000628:therapy; D012815:Signal Processing, Computer-Assisted
keywords: Brain–computer interface; Microelectrode array; Neural decoding; Non-causal filter; Spike sorting; Threshold crossing