Real-time two-dimensional asynchronous control of a computer cursor with a single subdural electrode.

OBJECTIVE: To test the feasibility of controlling a computer cursor asynchronously in two dimensions using one subdural electrode. DESIGN: Proof of concept study. SETTING: Acute care hospital in Toronto, Canada. PARTICIPANT: A 68-year-old woman with a subdural electrode implanted for the treatment of essential tremor (ET) using direct brain stimulation of the primary motor cortex (MI). INTERVENTIONS: Power changes in the electrocorticography signals were used to implement a "brain switch". To activate the switch the subject had to decrease the power in the 7-13 Hz frequency range using motor imagery of the left hand. The brain switch was connected to a system for asynchronous control of movement in two dimensions. Each time the user reduced the amplitude in the 7-13 Hz frequency band below an experimentally defined threshold the direction of cursor changed randomly. The new direction was always different from those previously rejected ensuring the convergence of the system on the desired direction. OUTCOME MEASURES: Training time, time and number of switch activations required to reach specific targets, information transfer rate. RESULTS: The user was able to control the cursor to specific targets on the screen after only 15 minutes of training. Each target was reached in 51.7 ± 40.2 seconds (mean ± SD) and after 9.4 ± 6.8 switch activations. Information transfer rate of the system was estimated to be 0.11 bit/second. CONCLUSION: A novel brain-machine interface for asynchronous two-dimensional control using one subdural electrode was developed.