04-06-2012, 10:19 AM
Breaking the silence: Brain–computer interfaces (BCI)
for communication and motor control
Breaking the silence.pdf (Size: 2.49 MB / Downloads: 80)
Abstract
Brain–computer interfaces (BCI) allow control of computers or external devices with regulation of brain activity alone.
Invasive BCIs, almost exclusively investigated in animal models using implanted electrodes in brain tissue, and
noninvasive BCIs using electrophysiological recordings in humans are described. Clinical applications were reserved
with few exceptions for the noninvasive approach: communication with the completely paralyzed and locked-in
syndrome with slow cortical potentials, sensorimotor rhythm and P300, and restoration of movement and cortical
reorganization in high spinal cord lesions and chronic stroke. It was demonstrated that noninvasive EEG-based BCIs
allow brain-derived communication in paralyzed and locked-in patients but not in completely locked-in patients. At
present no firm conclusion about the clinical utility of BCI for the control of voluntary movement can be made.
Invasive multielectrode BCIs in otherwise healthy animals allowed execution of reaching, grasping, and force variations
based on spike patterns and extracellular field potentials.
A brain–computer interface (BCI) or brain–machine interface
(BMI) activates electronic or mechanical devices with brain activity
alone. BCIs and BMIs allow direct brain communication in
completely paralyzed patients and restoration of movement in
paralyzed limbs through the transmission of brain signals to the
muscles or to external prosthetic devices. We differentiate invasive
from noninvasive BCIs: Invasive BCIs use activity recorded
by brain implanted micro- or macroelectrodes, whereas noninvasive
BCIs use brain signals recorded with sensors outside the
body boundaries.
History of BCI Research
Hans Berger, who discovered the human EEG, speculated in his
first comprehensive review of his experiments with the ‘‘Elektrenkephalogramm’’
(1929) about the possibility of reading
thoughts from the EEG traces by using sophisticated mathematical
analyses. Grey Walter, the brilliant EEG pioneer who described
the contingent negative variation (CNV), often called the
‘‘expectancy wave,’’ built the first automatic frequency analyzer
and the computer of ‘‘average transients’’ with the intention of
discriminating covert thoughts and language in the human EEG
(Walter, 1964). Fetz (1969) published the first paper on invasive
operant conditioning of cortical spike trains in animals. Only the
recent development of BCIs, however, has brought us a bit closer
to the dreams of these pioneers of EEG research.
Seizure Control
The most spectacular and popularized results in the emerging
field of biofeedback (or ‘‘physiological regulation’’ as it is presently
called) were the self-regulation of brain waves (Kamiya,
1971). Increase and decrease of alpha frequency of the EEGwere
supposed to create ‘‘meditative’’ states with many beneficial effects
in the periphery and on behavior. Theta wave augmentation
and reduction had profound effects on vigilance and attention
(Birbaumer, 1977). Slowcortical potentials (SCP) control allowed
anatomically specific voluntary regulation of different brain areas
with area specific effects on behavior and cognition (for an overview,
see Rockstroh, Elbert, Birbaumer, & Lutzenberger, 1989).
Warning voices such as experiments by Mulholland and his group
(Mullholland & Evans, 1966) demonstrating perfect control of
alphawaves throughmanipulation of the oculomotor systemand
decoupling of eye fixation went largely unheard.
Invasive BCIs for Communication
Kennedy, Kirby, Moore, King, and Mallory (2004) published
several single cases with ALS in different stages (none either LIS
or CLIS), with a cortically implanted glass microelectrode filled
with a neurotrophic growth factor. The axon of the cell targeted
by the electrode grows into it and allows recording of the spike
activity. Some of the patients learned to spell using the spike
activity mainly by turning it on and off in a ‘‘yes’’ or ‘‘no’’ fashion.
From the published material, it is difficult to judge the usefulness
of this preparation because death and medical
complications interrupted communication in several cases (one
case reportedly used the device on a more continuous basis).
Epilog
Brain–computer interfaces or brain–machine interfaces are intended
to translate ‘‘thought into action’’ with brain activity
only. The research devoted to this goal has raised many fascinating
questions about brain–behavior relationships without
achieving its ultimate practical goals: communication with the
completely paralyzed and restoration of movement in paralysis.