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http://computer.howstuffworks.com/brain-computer-interface.htm/printable
How Brain-computer Interfaces Work
by Ed Grabianowski
Browse the article How Brain-computer Interfaces Work
Introduction to How Brain-Computer Interfaces Work
As the power of modern computers grows alongside our understanding of the
human brain, we move ever closer to making some pretty spectacular science
fiction into reality. Imagine transmitting signals directly to someone's
brain that would allow them to see, hear or feel specific sensory inputs.
Consider the potential to manipulate computers or machinery with nothing
more than a thought. It isn't about convenience -- for severely disabled
people, development of a brain-computer interface (BCI) could be the most
important technological breakthrough in decades. In this article, we'll
learn all about how BCIs work, their limitations and where they could be
headed in the future.
The Electric Brain
The reason a BCI works at all is because of the way our brains function. Our
brains are filled with neurons, individual nerve cells connected to one
another by dendrites and axons. Every time we think, move, feel or remember
something, our neurons are at work. That work is carried out by small
electric signals that zip from neuron to neuron as fast as 250 mph [source:
Walker]. The signals are generated by differences in electric potential
carried by ions on the membrane of each neuron.
Although the paths the signals take are insulated by something called
myelin, some of the electric signal escapes. Scientists can detect those
signals, interpret what they mean and use them to direct a device of some
kind. It can also work the other way around. For example, researchers could
figure out what signals are sent to the brain by the optic nerve when
someone sees the color red. They could rig a camera that would send those
exact signals into someone's brain whenever the camera saw red, allowing a
blind person to "see" without eyes.
In the next section, we'll learn about the basics of the interface itself.
BCI Input and Output
One of the biggest challenges facing brain-computer interface researchers
today is the basic mechanics of the interface itself. The easiest and least
invasive method is a set of electrodes -- a device known as an
electroencephalograph (EEG) -- attached to the scalp. The electrodes can
read brain signals. However, the skull blocks a lot of the electrical
signal, and it distorts what does get through.
To get a higher-resolution signal, scientists can implant electrodes
directly into the gray matter of the brain itself, or on the surface of the
brain, beneath the skull. This allows for much more direct reception of
electric signals and allows electrode placement in the specific area of the
brain where the appropriate signals are generated. This approach has many
problems, however. It requires invasive surgery to implant the electrodes,
and devices left in the brain long-term tend to cause the formation of scar
tissue in the
gray matter. This scar tissue ultimately blocks signals.
Regardless of the location of the electrodes, the basic mechanism is the
same: The electrodes measure minute differences in the voltage between
neurons. The signal is then amplified and filtered. In current BCI systems,
it is then interpreted by a computer program, although you might be familiar
with older analogue encephalographs, which displayed the signals via pens
that automatically wrote out the patterns on a continuous sheet of paper.
In the case of a sensory input BCI, the function happens in reverse. A
computer converts a signal, such as one from a video camera, into the
voltages necessary to trigger neurons. The signals are sent to an implant in
the proper area of the brain, and if everything works correctly, the neurons
fire and the subject receives a visual image corresponding to what the
camera sees.
Another way to measure brain activity is with a Magnetic Resonance Image
(MRI). An MRI machine is a massive, complicated device. It produces very
high-resolution images of brain activity, but it can't be used as part of a
permanent or semipermanent BCI. Researchers use it to get benchmarks for
certain brain functions or to map where in the brain electrodes should be
placed to measure a specific function. For example, if researchers are
attempting to implant electrodes that will allow someone to control a
robotic arm with their thoughts, they might first put the subject into an
MRI and ask him or her to think about moving their actual arm. The MRI will
show which area of the brain is active during arm movement, giving them a
clearer target for electrode placement.
So, what are the real-life uses of a BCI? Read on to find out the
possibilities.
BCI Applications
One of the most exciting areas of BCI research is the development of devices
that can be controlled by thoughts. Some of the applications of this
technology may seem frivolous, such as the ability to control a video game
by thought. If you think a remote control is convenient, imagine changing
channels with your mind.
However, there's a bigger picture -- devices that would allow severely
disabled people to function independently. For a quadriplegic, something as
basic as controlling a computer cursor via mental commands would represent a
revolutionary improvement in quality of life. But how do we turn those tiny
voltage measurements into the movement of a robotic arm?
Early research used monkeys with implanted electrodes. The monkeys used a
joystick to control a robotic arm. Scientists measured the signals coming
from the electrodes. Eventually, they changed the controls so that the
robotic arm was being controlled only by the signals coming form the
electrodes, not the joystick.
A more difficult task is interpreting the brain signals for movement in
someone who can't physically move their own arm. With a task like that, the
subject must "train" to use the device. With an EEG or implant in place, the
subject would visualize closing his or her right hand. After many trials,
the software can learn the signals associated with the thought of
hand-closing. Software connected to a robotic hand is programmed to receive
the "close hand" signal and interpret it to mean that the robotic hand
should close. At that point, when the subject thinks about closing the hand,
the signals are sent and the robotic hand closes.
A similar method is used to manipulate a computer cursor, with the subject
thinking about forward, left, right and back movements of the cursor. With
enough practice, users can gain enough control over a cursor to draw a
circle, access computer programs and control a TV [source: Ars Technica]. It
could theoretically be expanded to allow users to "type" with their
thoughts.
Once the basic mechanism of converting thoughts to computerized or robotic
action is perfected, the potential uses for the technology are almost
limitless. Instead of a robotic hand, disabled users could have robotic
braces attached to their own limbs, allowing them to move and directly
interact with the environment. This could even be accomplished without the
"robotic" part of the device. Signals could be sent to the appropriate motor
control nerves in the hands, bypassing a damaged section of the spinal cord
and allowing actual movement of the subject's own hands.
On the next page we'll learn about cochlear implants and artificial eye
development.
Sensory Input
The most common and oldest way to use a BCI is a cochlear implant. For the
average person, sound waves enter the ear and pass through several tiny
organs that eventually pass the vibrations on to the auditory nerves in the
form of electric signals. If the mechanism of the ear is severely damaged,
that person will be unable to hear anything. However, the auditory nerves
may be functioning perfectly well. They just aren't receiving any signals.
A cochlear implant bypasses the nonfunctioning part of the ear, processes
the sound waves into electric signals and passes them via electrodes right
to the auditory nerves. The result: A previously deaf person can now hear.
He might not hear perfectly, but it allows him to understand conversations.
The processing of visual information by the brain is much more complex than
that of audio information, so artificial eye development isn't as advanced.
Still, the principle is the same. Electrodes are implanted in or near the
visual cortex, the area of the brain that processes visual information from
the retinas. A pair of glasses holding small cameras is connected to a
computer and, in turn, to the implants. After a training period similar to
the one used for remote thought-controlled movement, the subject can see.
Again, the vision isn't perfect, but refinements in technology have improved
it tremendously since it was first attempted in the 1970s. Jens Naumann was
the recipient of a second-generation implant. He was completely blind, but
now he can navigate New York City's subways by himself and even drive a car
around a parking lot [source: CBC News]. In terms of science fiction
becoming reality, this process gets very close. The terminals that connect
the camera glasses to the electrodes in Naumann's brain are similar to those
used to connect the VISOR (Visual Instrument and Sensory Organ) worn by
blind engineering officer Geordi La Forge in the "Star Trek: The Next
Generation" TV show and films, and they're both essentially the same
technology. However, Naumann isn't able to "see" invisible portions of the
electromagnetic spectrum.
On the next page, find out about the inherent limitations of brain-computer
interfaces -- and also learn about some exciting innovations.
BCI Drawbacks and Innovators
Although we already understand the basic principles behind BCIs, they don't
work perfectly. There are several reasons for this.
1.. The brain is incredibly complex. To say that all thoughts or actions
are the result of simple electric signals in the brain is a gross
understatement. There are about 100 billion neurons in a human brain
[source: Greenfield]. Each neuron is constantly sending and receiving
signals through a complex web of connections. There are chemical processes
involved as well, which EEGs can't pick up on.
2.. The signal is weak and prone to interference. EEGs measure tiny
voltage potentials. Something as simple as the blinking eyelids of the
subject can generate much stronger signals. Refinements in EEGs and implants
will probably overcome this problem to some extent in the future, but for
now, reading brain signals is like listening to a bad phone connection.
There's lots of static.
3.. The equipment is less than portable. It's far better than it used to
be -- early systems were hardwired to massive mainframe computers. But some
BCIs still require a wired connection to the equipment, and those that are
wireless require the subject to carry a computer that can weigh around 10
pounds. Like all technology, this will surely become lighter and more
wireless in the future.
BCI Innovators
A few companies are pioneers in the field of BCI. Most of them are still in
the research stages, though a few products are offered commercially.
a.. Neural Signals is developing technology to restore speech to disabled
people. An implant in an area of the brain associated with speech (Broca's
area) would transmit signals to a computer and then to a speaker. With
training, the subject could learn to think each of the 39 phonemes in the
English language and reconstruct speech through the computer and speaker
[source: Neural Signals].
b.. NASA has researched a similar system, although it reads electric
signals from the nerves in the mouth and throat area, rather than directly
from the brain. They succeeded in performing a Web search by mentally
"typing" the term "NASA" into Google [source: New Scientist].
c.. Cyberkinetics Neurotechnology Systems is marketing the BrainGate, a
neural interface system that allows disabled people to control a wheelchair,
robotic prosthesis or computer cursor [source: Cyberkinetics].
d.. Japanese researchers have developed a preliminary BCI that allows the
user to control their avatar in the online world Second Life [source: Ars
Technica].
To learn more about brain-computer interfaces, take a look at the links on
the next page.
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