Brain–Computer Interfaces - Index of

230 J.E. Huggins
6 Past and Present ECoG Research for BCI
Although human ECoG has been used for scientific study of brain function and neurological
disorders since at least the 1960s [e.g. [18]], its use for BCI research was
almost nonexistent prior to the 1990s. The earliest BCI researchers either worked
with animals to develop tools for recording the activity of individual neurons (e.g.,
[16, 19]) or worked with human EEG (e.g.[20, 21]).
6.1 ECoG Animal Research
The first ECoG studies for BCI development were reported in 1972 by Brindley
and Craggs [22, 23] who studied the signals from epidural [22] electrode arrays
implanted over the baboon motor cortex [22, 23]. ECoG was bandpass filtered to
80–250 Hz and the mean square of the signal calculated to produce a characteristic
signal shape preceding specific movements that was localized over arm or leg motor
cortex. A simple threshold detector was applied to this feature, generating prediction
accuracy as high as 90%.
6.2 Human ECoG Studies
6.2.1 Smith-Kettlewell Eye Research Institute
The first human BCI work using ECoG was reported in 1989 by Sutter [8, 24].
Epidurally implanted electrodes over visual cortex provided the input to a corticallybased
eyegaze tracking system. The system was developed and tested using visual
evoked potentials (VEP) in EEG. However, implanted electrodes were used when a
subject with ALS had difficulty with artifact due to uncontrolled muscle activity and
signal variations due to variable electrode placement by caregivers. Subjects viewed
a grid of 64 flickering blocks. The block at the center of the subject’s field of vision
could be identified because the lag between stimulus and VEP onset was known.
While this interface did not claim to be operable without physical movement, and is
therefore not a “true” BCI, it did demonstrate the use of large intracranial electrodes
as the signal source for an assistive technology interface.
6.2.2 The University of Michigan – Ann Arbor (Levine and Huggins)
Levine and Huggins’ UM-DBI project was the first targeted exploration of human
ECoG for BCI development [3, 25, 26]. The UM-DBI project recorded from their
first subject on the 27th July 1994. The UM-DBI project has focused on the detection
of actions in a continuous segment of ECoG data during which subjects repeated
actions at their own pace. ECoG related to actual movement has been used almost
exclusively to allow good documentation of the time at which the subject chose to
do the action.