Decoding movement-related cortical potentials from electrocorticography.
OBJECTIVE
Control signals for brain-machine interfaces may be obtained from a variety of sources, each with their own relative merits. Electrocorticography (ECoG) provides better spatial and spectral resolution than scalp electroencephalography and does not include the risks attendant upon penetration of the brain parenchyma associated with single and multiunit recordings. For these reasons, subdural electrode recordings have been proposed as useful primary or adjunctive control signals for brain-machine interfaces. The goal of the present study was to determine if 2D control signals could be decoded from ECoG.


METHODS
Six patients undergoing invasive monitoring for medically intractable epilepsy using subdural grid electrodes were asked to perform a motor task involving moving a joystick in 1 of 4 cardinal directions (up, down, left, or right) and a fifth condition ("trigger"). Evoked activity was synchronized to joystick movement and analyzed in the theta, alpha, beta, gamma, and high-gamma frequency bands.


RESULTS
Movement-related cortical potentials could be accurately differentiated from rest with very high accuracy (83-96%). Further distinguishing the movement direction (up, down, left, or right) could also be resolved with high accuracy (58-86%) using information only from the high-gamma range, whereas distinguishing the trigger condition from the remaining directions provided better accuracy.


CONCLUSIONS
Two-dimensional control signals can be derived from ECoG. Local field potentials as measured by ECoG from subdural grids will be useful as control signals for a brain-machine interface.
Reddy
Chandan G
CG
Department of Neurosurgery, University of Iowa Hospitals, Iowa City, Iowa, USA. chandan-reddy@uiowa.edu
Reddy
Goutam G
GG
Kawasaki
Hiroto
H
Oya
Hiroyuki
H
Miller
Lee E
LE
Howard
Matthew A
MA
D000328:Adult; D002540:Cerebral Cortex / Q000502:physiology*; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000379:methods / Q000706:statistics & numerical data*; D004827:Epilepsy / Q000175:diagnosis; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008328:Man-Machine Systems; D009043:Motor Activity / Q000502:physiology; D009068:Movement / Q000502:physiology*; D012815:Signal Processing, Computer-Assisted; D013355:Subdural Space / Q000502:physiology; D014584:User-Computer Interface