Brain–Computer Interfaces - Index of

Brain–Computer Interface in Neurorehabilitation 157
Figure 1 shows the most frequently used EEG BCI. More recently, a BCI system
based on magnetoencephalography was tested [8] and applied to stroke rehabilitation.
On an experimental basis near-infrared spectroscopy (NIRS) and functional
magnetic resonance-BCIs were introduced by our group [33, 10]. Of particular
interest is the use of signals ranging in spatial resolution between single spikes and
local field potentials (LFP) and the EEG, namely the electrocorticogramm (ECoG).
Electrical signals recorded subdurally or epidurally provide a better spatial resolution
with the same exquisite time resolution as EEG but avoids the smearing
and filtering of the EEG signals. In addition, it allows recording and training of
high frequency components particularly in the gamma range (from 30 to 100 Hz).
First attempts to classify movement directions from the electrocorticogramm were
particularly successful (see [2, 22, 35, 38]; see also chapters “BCIs Based on
Signals from Between the Brain and Skull” and “A Simple, Spectral-change Based,
Electrocorticographic Brain–Computer Interface” in this book). At present, brain–
computer interface research in neurorehabilitation is dominated by interesting basic
science approaches holding great promises for human applications but very modest
clinical use (see [7]). As in the tradition of clinical applications of neurofeedback,
the field is lacking large-scale clinical studies with appropriate controls proving the
superior efficiency of BCI systems over classical rehabilitation attempts.
2 Basic Research
Animal research stimulated to a large extent the interest and enthusiasm in BCI
research. Nicolelis [26, 27] summarized these attempts: using more than 100 electrodes
in the motor cortex or in the parietal cortex projecting into the motor system
monkeys were trained to move a prosthesis mounted outside their body or even
in another laboratory using spike sequences; monkeys were trained over long time
periods to move prostheses with spike frequencies and were rewarded when the
peripheral orthoses performed an aiming or reaching movement usually grapping a
food reward. Even more impressive were studies from the laboratory of Eberhard
Fetz [15] with operant conditioning of spike sequences. Monkeys were able to produce
many different types of single cell activity, rhythmic and non-rhythmic, and
used the trained spike sequences for manipulating external machinery. Of particular
interest was the demonstration of a neurochip in which the monkey learned to
operate an electronic implant with action potentials recorded on one electrode to
trigger electrical stimuli delivered to another location on the cortex. After several
days of training, the output produced from the recording site shifted to resemble
the output from the corresponding stimulation site, consistent with a potentiation of
synaptic connections between the artificially synchronized neurons. The monkeys
themselves produced long-term motor cortex plasticity by activating the electronic
neuronal implant. These types of Hebbian implants may turn out to be of fundamental
importance for neurorehabilitation after brain damage using the brain–computer
interface to permanently change cortical plasticity in areas damaged or suppressed
by pathophysiological activity.