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BCI Meeting 2005—Workshop on Signals and
Recording Methods
Jonathan R. Wolpaw, Gerald E. Loeb, Brendan Z. Allison,
Emanuel Donchin, Omar Feix do Nascimento,
William J. Heetderks, Femke Nijboer, William G. Shain, and
James N. Turner
Abstract—This paper describes the highlights of presentations and discussions during the Third International BCI Meeting in a workshop that
evaluated potential brain–computer interface (BCI) signals and currently
available recording methods. It defined the main potential user populations
and their needs, addressed the relative advantages and disadvantages of
noninvasive and implanted (i.e., invasive) methodologies, considered ethical issues, and focused on the challenges involved in translating BCI systems from the laboratory to widespread clinical use. The workshop stressed
the critical importance of developing useful applications that establish the
practical value of BCI technology.
Index Terms—Brain–computer interface (BCI), electrophysiological signals, rehabilitation.
I. INTRODUCTION
This workshop, which was part of the 2005 BCI meeting, addressed
the characteristics, advantages, and disadvantages for brain–computer
interface (BCI) use of different brain signals and recording methods
with particular reference to development of clinical applications. The
major issues considered included the characteristics, capacities, and
needs of people likely to benefit from a BCI; the advantages and disadvantages of electroencephalographic (EEG), electrocorticographic
(ECoG), and intracortical signals; other possible signal modalities; the
ethical issues associated with BCI research and use; and the transition from the laboratory to widespread clinical use. The participants
Manuscript received February 27, 2006; revised March 27, 2006. The National Institutes of Health (i.e., The National Institute of Biomedical Imagining
and Biomedical Engineering, the National Center for Medical Rehabilitation
Research of the National Institute of Child Health and Human Development,
the National Institute on Deafness and Other Communication Disorders,
and the Office of Rare Diseases) provided major funding for this meeting
(R13EB00511401). Additional funding for the participation of students and
postdoctoral fellows was provided by: The National Science Foundation;
the Department of Defense Advanced Research Project Agency (DARPA);
the Wadsworth Center (New York State Department of Health); Honeywell
International; Cyberkenetics Neurotechnology Systems, Inc.; the Alfred E.
Mann Foundation; g.tec Guger Technologies OEG; Cortech Solutions, LLC;
and Cleveland Medical Devices, Inc.
The authors are with Wadsworth Center, Albany, NY 12201-0509 USA
(e-mail: wolpaw@wadsworth.org; gloeb@usc.edu; ballison@scripps.edu;
donchin@shell.cas.usf.edu;
omar@smi.auc.dk;
heetderw@mail.nih.gov;
femke.nijboer@uni-tuebingen.de; shain@wadsworth.org; turner@wadsworth.
org).
Digital Object Identifier 10.1109/TNSRE.2006.875583
included clinical and basic neuroscientists, cell biologists, engineers,
biophysicists, psychologists, and clinicians. The format included individual presentations and panel-led discussions.
II. USER POPULATIONS
BCI users are often categorized according to the disorders responsible for their disabilities, such as amyotrophic lateral sclerosis (ALS),
brainstem stroke, spinal cord injury, or cerebral palsy. However, decisions regarding whether or how BCI technology might be useful to
these users usually depend more on the extent of their disability than
on its origin. In this regard, potential users fall into three relatively distinct classes.
The first class consists of people who are truly totally locked-in (e.g.,
due to end-stage ALS or severe cerebral palsy), who have no remaining
useful neuromuscular control of any sort, including no eye movement.
Although this class is very small, it is often considered to be the first
target group for BCI applications. However, in reality, efforts to demonstrate effective BCI operation by these individuals encounter a number
of difficult challenges. It is often unclear, for example, whether cognitive functions remain intact, whether vision is adequate to support
BCI operation, and if not, whether an auditory or other alternative will
suffice, and whether the user can or will maintain a state of alertness
adequate for reliable BCI operation. In practice to date, these or related
issues have been major impediments to BCI usage by these users. Each
person requires a comprehensive and individualized approach that goes
far beyond the much simpler procedures effective in those who are not
totally locked-in. On the other hand, if people progressing toward this
level of disability (e.g., those in the early or middle stages of ALS)
begin to use BCI technology before they become totally locked-in, they
may be able to continue to use it effectively after they lose all motor
function.
The second class of potential BCI users comprises those who retain
a very limited capacity for neuromuscular control. This group includes
people who retain some useful eye movement or enough limb muscle
function to operate a single-switch system. Such control is often slow,
unreliable, or easily fatigued [5]. This group is much larger than the
first, and includes many people with late-stage ALS, brainstem stroke,
and severe cerebral palsy. The advent of widely available life-support
technology, particularly ventilators, enables these individuals to survive indefinitely, and numerous studies now show that with adequate
physical and social support they can lead lives that they and their families and friends consider worthwhile and enjoyable [12], [20], [23],
[27], [32], [45]. Thus, there is substantial impetus for developing BCI
communication and control technology for this group. Furthermore,
current or readily achievable BCI systems may provide communication
and control capacities (e.g., for simple word processing, environmental
control, entertainment access) comparable to, or even better than, that
achievable with their residual neuromuscular control.
The third class of potential BCI users, which is the largest of all,
includes those who still retain (and can be expected to continue to
retain) substantial neuromuscular control, particularly speech and/or
hand control, and can, therefore, operate a wide range of assistive communication and control devices. For this group, as well as for users
without disabilities, BCI technology, whether currently available or
likely to be available in the near future, has little to offer (though it
might be useful in very specific situations, such as when hands-free
control is required). It will only be if and when BCI speed, accuracy,
and precision of control substantially exceed current levels that this
technology will become a significant option for this class of potential
users.
1534-4320/$20.00 © 2006 IEEE
IEEE TRANSACTIONS ON NEURAL SYSTEMS AND REHABILITATION ENGINEERING, VOL. 14, NO. 2, JUNE 2006
139
Thus, at present, users of the second class (including those progressing toward the first class) constitute the principal candidates for
BCI communication and control applications. Substantial anecdotal
experience indicates that there are many such individuals with minimal
remaining useful motor function. People with late-stage ALS constitute the largest number. People with severe cerebral palsy, brainstem
stroke, and a variety of other neuromuscular disorders comprise the
rest of this group.
III. AVAILABLE CONTROL SIGNALS
While most BCI systems use electrical signals produced by brain
activity to derive user intent, a variety of other signals could conceivably be used (for review [1], [19], [42]). These include signals
obtained by functional magnetic resonance imaging (fMRI); near-infrared spectroscopy (NIRS); magnetoencephalography (MEG); and
positron emission tomography (PET) (e.g., [3], [6], [7], [10], [13],
[41], [44]). BCIs using fMRI or NIRS measure changes in the brain’s
hemodynamic response. Although they may provide good spatial
resolution, they have poor temporal resolution. In addition, fMRI
and PET require bulky expensive equipment and are technically
demanding. MEGs measure the brain’s magnetic activity, and hence
MEG BCIs might provide real-time control with excellent spatial
and temporal resolution. However, this option, like fMRI, requires a
superconductor and is, therefore, bulky, expensive, and impractical
for widespread clinical use. As a result, while other signal types merit
further research (particularly NIRS), only electrical signals are likely
to be of significant practical value for clinical use in the near future.
As Fig. 1 illustrates, the electrical fields produced by the brain can be
detected at the scalp (EEG), at the cortical surface (ECoG activity), or
within the cortex [local field potentials (LFPs) or neuronal action potentials (spikes)]. Each alternative has advantages and disadvantages. EEG
recording is easy and noninvasive. At the same time, however, it has
relatively limited topographical resolution and frequency range. It may
also be contaminated by artifacts such as electromyographic (EMG)
activity from cranial muscles or electrooculographic (EOG) activity.
While the potential speed and accuracy of EEG-based BCI operation
has often been assumed to be modest, recent studies (e.g., [43]) indicate that it can provide multichannel function previously thought to require implanted recording electrodes. At the same time, EEG requires
continued maintenance (presumably by caregivers) of stable relatively
low-impedance electrode contacts at specific locations on the scalp. In
addition, users may object to the cap or other device needed to maintain
the electrodes in place. Thus, more convenient and less conspicuous
EEG electrode methods are highly desirable (e.g., [36]).
Up to the present, surface cortical recording has been possible almost
exclusively from patients implanted with ECoG electrode arrays for a
few days prior to epilepsy surgery. Thus, while results are promising
(e.g., [22]), BCI ECoG studies have been very limited. ECoG has much
better topographical resolution and frequency range than EEG and is
essentially free from artifacts like EMG and EOG. Thus, ECoG has
substantial promise for BCI applications. At the same time, ECoG requires implantation of electrode arrays that have long-term stability
and give consistent performance. While the technology for permanent
implants exists, it has yet to be rigorously tested and configured for
clinical use. Furthermore, the nature and significance of the long-term
effects of such implants remain unknown and will require preclinical
studies in animals.
Intracortical recording, or recording in other brain structures, can
provide the highest resolution signals. These signals are individual
neuronal action potentials (spikes) or LFPs that reflect the combined
activity of nearby neurons and synapses. Most BCI-related work up
to the present has been in animals and has focused on spike activity
(e.g., [2], [30], [37], [38]). The few studies assessing LFPs suggest
Fig. 1. Brain’s electrical fields can be detected by electrodes (black) on the
scalp (EEG), on the cortical surface (ECoG activity), or within the brain [LFPs
and neuronal action potentials (spikes)]. See text for discussion.
that they may be as useful or more useful than spikes (e.g., [24]).
Limited human studies are underway (e.g., [14]). While the control
achieved has been reasonably impressive, long-term stability and
transferability from highly constrained laboratory situations to more
complex clinical environments remains uncertain. Most important,
this approach entails insertion of multiple electrode arrays within brain
tissue. Thus, it faces major as yet unresolved issues related to acute
and chronic tissue damage and long-term recording stability [11], [25],
[35], [39], [40]. Present-day arrays clearly evoke a complex continuing
process of tissue reaction [11], [18], [35], [39]. While some electrodes
may continue to function for long periods, many lose the ability to
record spike activity quite early [11], [40]. At the same time, recent
results are more encouraging [34], and efforts to reduce or control the
reaction to implanted arrays and thereby promote long-term functional
stability are just beginning [21], [26], [31], [33]. For intracortical
electrodes as for ECoG electrodes, long-term clinical use will require
wholly implanted technology that incorporates telemetry, because it is
essential to avoid the percutaneous connections that are used in acute
studies but provide routes for infection in long-term applications.
The eventual clinical value of each of these recording options will
reflect the capabilities of the communication and control applications
it can support and the degree to which its medical risks and technical
limitations can be overcome. The relative practical usefulness of EEG,
ECoG, and intracortical methods remains to be determined. Comprehensive evaluation of the characteristics, capacities, and safety of each
recording method is essential, and will be facilitated by software that
can be readily adapted to different signals and operating protocols (e.g.,
[29]).
IV. ETHICAL ISSUES
BCI research and development raises three sets of ethical issues. The
first set includes issues that confront any medical research effort that
involves any level of risk. In the case of BCI technology, it applies primarily to invasive methods, such as ECoG or intracortical recording.
Implantation of electrode arrays within brain or even just on the cortical
surface entails some measure of acute trauma. It may initiate prolonged
reactive processes leading to scarring and possibly significant neuronal
loss and risk of infection, particularly if long-term percutaneous connections are necessary. In addition, there is risk of functional failure
over time, leading to additional surgery for removal or replacement.
Human research investigations of implanted devices will require preclinical studies that address these risks and establish the usefulness of
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the technology. Risk–benefit considerations will ultimately determine
whether implanted devices (whether in or on the cortex) or noninvasive methods will best provide BCI function for a given patient. Animal research to establish methods to ensure long-term performance
of implanted devices and technology development to provide wireless
systems for data and information transfer from and to these devices
must be completed before they will be suitable for widespread clinical
application.
Beyond these standard questions of risks and benefits, all BCI research and development, whether it involves noninvasive or implanted
methods, raises two additional and unique sets of ethical issues. One is
the potential invasion of privacy inherent in the possibility that a BCI
might be used to obtain information (e.g., answers to specified questions) from a person without consent. However, most, and possibly all,
BCI-based communication requires active interaction between the user
and the BCI system. BCI usage is a voluntary and often effortful activity, similar to conventional voluntary motor acts, except that it does
not involve peripheral nerves and muscles. While P300-based methodology has been proposed as a promising new lie-detection method [8],
[9], [16], more recent work indicates that this technique does in fact
require the active participation of the individual [15], [28].
The other set of unique BCI-related ethical issues are those related
to the creation of cyborgs. A “cyborg,” as defined in the Oxford English Dictionary [4] is “a person whose. . . capabilities are extended beyond normal human limitations by a machine; an integrated man–machine system.” All BCIs, whether they use noninvasive or implanted
methods, take brain signals associated with normal brain activity and
convert them into a wholly new output channel. The brain’s normal
outputs are the result of complex interactions of cortical, subcortical,
and spinal cord neuronal populations, and are all expressed through
the spinal motoneurons that control muscles. Thus, the final outputs
undergo multilevel preprocessing. In contrast, BCIs take signals from
one or several brain areas and use them directly as control signals for
devices such as cursors or prostheses. Thus, BCIs essentially reformat
CNS operation, and create a cyborglike combination of brain and machine.
This CNS/BCI cyborg may have new capacities beyond those of the
normal CNS. It might, for example, be able to act more rapidly or to
control more outputs simultaneously. Of more potential concern is the
possibility that BCI usage could induce widespread changes in brain
functions that go well beyond changes in the brain area directly responsible for the BCI signals (e.g., [17]). Because activity-dependent
plasticity is ubiquitous throughout the CNS, continued BCI usage could
have complex long-term impact on other brain areas and on many aspects of CNS operation. Furthermore, a CNS/BCI cyborg might not
possess the same censoring capacities that oversee conventional neuromuscular output channels. Thus, inappropriate actions that would normally be considered and not executed might conceivably go forward
because they originated from the signals emanating from a particular
cortical area rather than from normal spinal motoneuron activation. The
present primitive state of BCI development means that such concerns
will remain only theoretical for the near future. Nevertheless, these issues are certainly interesting and potentially important and may require
substantial attention in the future.
V. MOVING FROM THE LABORATORY TO THE HOME
The purpose of BCI research and development is to restore communication and control capacities to people with severe motor disabilities.
Thus, this work must solve the problems attendant on transferring technology from the laboratory to widespread clinical use. There are at least
five critical issues.
First, the BCI must be easy to use. BCI operation must be simple
and straightforward so that it can be handled by the user and caregivers
on their own, with minimal continued technical support. Reliable electrodes and user-friendly software are necessary.
Second, the BCI must operate consistently in the user’s home
without significant disruption by electrical noise generated by ventilators, wheelchairs, household appliances, or other devices. Most
people with severe disabilities live surrounded by an extensive array
of electronic equipment.
Third, unlike most laboratory BCI systems, which tend to be physically large and complex, home BCI systems need to be compact so that
they occupy little space and have minimal impact on the user’s immediate environment.
Fourth, BCI use should not interfere with normal daily activities.
Users with severe disabilities have demanding schedules involving
many often prolonged interactions with caregivers, physiotherapists,
and other support personnel. BCI usage should improve these interactions, not impede them.
Fifth, and perhaps most important, the BCI must provide capacities
that the user actually wants. This is not a trivial requirement. Users
of assistive technology frequently want capacities different from those
that researchers or therapists may assume to be most desired. As a result, each home BCI installation will require careful preliminary discussions with user and caregiver and will almost certainly entail adjustments or specialized application implementations that are, to some
degree, unique to each user.
VI. CONCLUSION
At present and for the immediate future, BCI-based communication
and control will be most useful to people who retain only minimal
and unreliable voluntary muscle control; and clinically useful BCIs
are likely to be those that use electrophysiological signals, whether
obtained noninvasively from scalp electrodes or invasively from implanted devices. The relative advantages and disadvantages of the different electrophysiological BCI methods remain uncertain, and their
clarification will require careful human and animal studies. BCI research and development raises standard ethical issues and unique ethical issues related to their possible abuse and to their probable complex
effects on CNS function. Achievement of the central goal of BCI research—communication and control for those for whom conventional
assistive technology is inadequate—will require home BCI systems
that are effective, easy to use, reliable, and inobtrusive.
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