Neuroscientist Theodore Berger is working real hard to be the
first person to implant microchips between your ears.
By Samuel Greengard
Clad in slacks and a dress shirt, Theodore Berger sits in his
cluttered office, surrounded by the flotsam and jetsam of his
work: modems, Zip drives, electrostatic bags, manuals, floppy
disks, white cotton gloves, books. The intense neurobiologist is
talking neurons and silicon chips, dendrite tissue and advanced
photonics. Beneath the wall-mounted photographs of brain tissue
and schematic diagrams of VLSI chips sit a pair of Gateway 2000
Pentium PCs. Their hard plastic outer cases have been removed, the
inside electronics ready for quick exploration. It's an
unmistakable metaphor for a guy who finds the bony cranium an
incidental obstacle to studying gray matter.
During the past four years, Berger and a seven-member team of
scientists - experts in everything from semiconductors to the
neurophysiology of tissue cultures - have worked ceaselessly at
the University of Southern California in Los Angeles to unlock the
brain's complex mathematical model so they can bridge the gap
between silicon and cerebrum. "If we can speak to the brain in its
own language then we begin to understand the biological basis of
thought and learning," says the 46-year-old scientist. "It's a
matter of understanding the way neurons act and react in every
conceivable situation, then building a device that can duplicate
their basic functions and transmit the appropriate electrical
impulses."
If Berger can link the two - computer and brain - he may create a
parallel- processing network that could function as a brain
implant. Such a device would restore physical and mental functions
lost to stroke, head trauma, Alzheimer's, epilepsy, and an array
of other maladies. His plan to create a bionic brain is bold,
brash, and just a bit, well, mind-blowing. Berger - scientist,
tinkerer, dreamer - wants to be the man who implants microchips
between your ears. And the amazing thing is that he just might
succeed.
Simple problem, complex solution
Understanding the human brain is a formidable task. Parked inside
the average cranium are between 1 and 10 billion neurons.
Extensions called dendrites relay electrical impulses to other
neurons, the brain cells that serve as the basic building blocks
of thought and activity. The electrical impulses are carried on
fibers called axons. The result is a neural network of remarkable
complexity.
The power of neurons is that they can work together in different
ways to produce speech, vision, hearing, and thought. Only when
something goes terribly wrong are we aware of how serious it is to
lose these connections. Only then are we able to recognize how
difficult it is to regain what's lost and how much therapy may be
required.
Neuroscience, a field that didn't exist until the mid-1960s, has
struggled to map the human brain and comprehend how all the
piecesfit together. It's analogous to a space alien dissecting
computers, robots, and other devices stuffed with semiconductors.
Without a road map, it would be virtually impossible to know what
each chip does and how it interacts with other microprocessors.
A decade ago, when Berger began studying "wet" brain tissue taken
from animals, he saw how little was known about the way neurons
process information, or how populations of neurons can work
together. Although scientists know a great deal about the
functioning of the individual nerve cells that compose the
hippocampus - the part of the brain that oversees memory - there's
still no clear idea of how their interaction produces the
cognitive function known as learning. "A great deal of classical
neurophysiology is devoted to trying to understand how the neurons
process the signal and what the output represents," he explains.
That's not a nagging concern for Berger. Instead, he spends 12 to
14 hours a day identifying and cataloging predictable and
repeatable neural electrical patterns, continuing a pattern of
neural/technical intervention that has been explored for decades.
In the 1950s, for instance, a stir was caused by a famous
experiment on rats by J. Olds and P. Milner. Electrodes were
implanted in each rat's lateral hypothalamus and connected to a
stimulator that could be activated by pressing a small button.
Since the electrical stimulation caused feelings of pleasure, the
rats soon learned to stimulate themselves, choosing that button
rather than another that would provide them with food, even when
they were hungry.
A decade later, American neurophysiologist J. M. R. Delgado used
stereotactic instruments to implant microelectrodes in precisely
targeted areas within the brain. Their signals were transmitted
wirelessly, making it possible to send high-voltage current. That
led to drastic changes in emotional, sexual, and social behavior.
In one dramatic demonstration, Delgado implanted an electronic
receiver in the medial region of the hypothalamus of a bull and
then challenged the animal to do battle in a bullfighting ring.
Delgado stopped the charging bull at the last minute by activating
electrodes with a radio transmitter.
More recent experiments by researchers like Caltech's Carver Mead
have shown that the elementary operations found in the nervous
system can be realized by analog circuits created with standard
silicon fabrication technology. Many neural areas are organized as
thin sheets and carry two-dimensional representations of their
computational space. These structures map well onto the
two-dimensional silicon surface. Coincidentally, in both neural
and silicon technologies, the active devices (synapses and
transistors) occupy no more than a small percentage of the space -
"wire" fills the remaining area.
Berger and fellow team member Vasilis Marmarelis, a professor of
biomedical engineering, have built on those insights through an
elaborate game of copycat, developing a complicated mathematical
model that precisely replicates the input and output signals that
a natural neural system uses. Just as a basketball player doesn't
require a degree in advanced trigonometry to toss a jump shot
through a hoop, Berger doesn't need to unlock the vast secrets of
the brain to make an implant work.
Wander into Berger's lab and you begin to see where he's going
with all this. Alongside a workbench covered with beakers and
tubes, a researcher (in the finest tradition of a Carnegie Deli
chef) slices human brain tissue into ultrathin sections. These
samples are then inserted into test tubes filled with oxygen and
artificial cerebral-spinal fluid, which keeps the fresh tissue
alive for several hours. The sample is transported to another part
of the lab, where a series of electrodes and probes are inserted.
This leads to a smorgasbord of electronic amplifiers and
oscilloscopes.
For the next few hours, the tissue is subjected to a series of
electronic impulses designed to simulate every possible
combination that the brain can throw at it. A Pentium computer
charts the data, creates a unique profile for each piece of
tissue, and then slots the information into an enormous database.
Berger & Co. repeat this process thousands of times. It's not
enough to know how a piece of brain tissue reacts to different
circumstances. They must understand the range of responses to the
same stimulus at different times.
Hardwiring the head
Constructing a brain implant is more than a meat-and-test-tube
operation, however. Even with a growing understanding of the
mathematics involved in driving such a system, today's digital
microprocessors are not fast enough to execute the complex
instructions in real time. Minutes, hours, even days could elapse
before a software-driven brain implant could process even the most
basic task, such as moving a finger that has been paralyzed by
stroke or restoring a fragment of memory lost to Alzheimer's.
Imagine trying to surf the Web on a 300-bps modem or commute to
work in a go-cart. Possible? Yes. Practical? Definitely not.
That's where silicon and hybrid analog/digital microchips enter
the picture. By hardwiring the algorithms that represent, say, 100
neurons onto a microchip, it is possible to rapidly accelerate the
data processing. A calculation that might have taken 10 seconds or
more in the past is now completed in only about 100 nanoseconds.
What's more, these neural microchips can operate as
parallel-processing devices.
But there's still a long way to go. Putting the function of
perhaps 100 or 200 neurons on a single chip and then hardwiring
tens of thousands of chips together would replicate only a
fraction of the 4 or 5 million neurons in the hippocampus. You'd
need an implant device the size of a pickup to get anywhere near
the processing power of the brain.
Armand R. Tanguay Jr., director of the Center for Neural
Engineering at USC and a key member of the team, hopes to solve
the scaling and bandwidth problems through a combination of
holography and laser optics. By using light signals to replace
physical wiring, it's possible to tightly stack 1-by-1-centimeter
chips, which can then communicate with each other. This tiny
parallel-processing network potentially allows for real-time
response, and might eventually fit into a space the size of a
peanut or, more important, the human skull.
Such an implant could be tailored to replace a lost ability in
humans. "Because the brain is such an adaptive organ," Berger
says, "the device wouldn't have to precisely mimic the lost
functions. If the brain is provided with a basic set of
instructions, it would fill in the blanks and regain the lost
functions. Over days and weeks, the person might make a full
recovery."
It's tough, time-consuming work, but engineering an implant from
the silicon up is a bit easier when you've got your own photonic
fabrication facility on the premises. Just a few hundred feet from
Berger's lab is a US$10 million setup that has the ability to make
the photonic elements that "wire" the silicon chips together, as
well as the multielectrode probes that act as an interface between
living and man-made neural circuits.
Surrounded by an array of equipment that would seem more fitting
in Silicon Valley than downtown LA - including a bonding machine
and clean room that can filter down to 10 particles per cubic foot
- assistant professor Chris Kyriakakis shows off a hybrid optical
electronic device that contains a set of stacked chips. "It has
the built-in electronics to power the entire device," he explains.
"The first chip drives another optical chip that can modulate
light. Ultimately, that's what runs the tiny computer network."
The final and most difficult step is placing such a device inside
the skull and connecting it to a living brain. Crosswiring such
wildly divergent universes - one brains, the other bytes - isn't
for the faint of heart or the intellectually timid. It's certainly
not difficult to let your imagination run amok and conjure up an
image of some crazed zombie straight out of a Boris Karloff flick.
But Berger is no Boris. Although Berger eschews much of the
conventional wisdom that permeates the rarefied field of
neuroscience - particularly traditional reductionist thinking that
says every piece of the puzzle must be fully understood in order
to build a scientific model - he also knows that it's crucial to
retain credibility within the discipline by adhering to accepted
standards and practices.
You might call his attitude skeptically reverent. "History is
littered with the debris of firmly established explanations that
have suddenly been overturned by new information," he says. "There
are countless cases where humanity believed that an explanation
was absolutely right, and then someone else came along with a
radically different explanation that washed the old theory down
the drain. So, it is very difficult to accept the truth of the
day. It's crucial to look at various perspectives and
explanations, to always keep the big picture in mind."
Berger seems to do that pretty well, though his approach perturbs
some in the scientific community. Having grown up in a household
that placed a high premium on introspection and accomplishment
("Not necessarily the accomplishment that comes with dollars, but
the accomplishment of having an impact on the people around you,"
he explains), and with a father who helped pioneer transistor
research at IBM, he realized early on that he wanted to make a
real difference in the world.
Berger studied mathematics and psychology at college but shied
away from a career in psychology, opting instead for the hands-on
world of neuroscience. "I realized that psychology doesn't have
the tools to fully understand the cause and effect of behavior,"
he says. "It is a very incomplete part of the puzzle."
Fast-forward a couple of decades, and Berger's life puzzle is
mostly assembled. He lives in a pleasant split-level home
overlooking the bluffs and beaches of Palos Verdes, commuting the
40 minutes to work in a 1992 Honda Accord. He spends spare moments
gardening or tinkering with computers; both allow him to further
explore elaborate relationships as well as evolution. Then there's
his wife and his 7-year-old daughter, the latter serving as his
most prized experiment. "Watching her brain develop is
fascinating," he observes. "You realize that there are some things
you can influence and some things you can't. You can try to teach
something to someone, but if the brain isn't ready or willing to
accept it, it ain't goin' in."
Which is precisely the challenge of Berger's odyssey into the
mind. Dropping a functioning brain implant into a person's head
and expecting it to work requires a voyage beyond the flat earth
of today's neuroscience. For starters, the shape of the
hippocampus doesn't remotely resemble a computer board, so
inserting a conventional microchip into the brain and trying to
send electrical waves back and forth would be like speaking into a
telephone that's not connected to anything. Berger has
circumvented this problem with a digital interface chip that will
serve as the gateway between the brain's cells and the stacked set
of chips that creates a group of artificial neurons.
Since transistors and neurons both send and receive electrical
signals, it all boils down to arranging the chip's conductors in a
pattern that matches the layout of neurons in a particular part of
the brain. The brain then believes it's receiving its own signals,
when in fact they're originating from the computer network. "A
transistor can send electricity and so can a neuron," Berger says.
"So, instead of using a computer chip that has transistors on it,
you build a chip with a piece of exposed metal. You place the
metal right next to the neuron, so that it can sense the
electrical signals sent out by the neuron and send signals to the
neuron." By slightly overbuilding the device - designing a layer
of electrodes that are perhaps 30 microns thick compared with the
cell's layer of 20 microns - Berger increases the odds of a
successful contact.
"The ever present scaling issue"
In almost all cases, electrical signals trigger the release of
chemical reactions in the brain, which in turn stimulate other
cells to produce electrical reactions. These result in additional
chemical activity. In fact, Berger points out that cells cannot
talk to each other without the release of chemicals that
effectively bridge the gap between neurons. So, the brain implant
would need only to stimulate electrical activity to work. Many
chemical imbalances would still be treated by medication, which
allows the brain to restore the proper electrical activity.With
all the parts in place, Berger will have essentially created a
circuit between the device and the gray matter that operates much
like a dedicated phone line. Brain cells could actually grow on
top of the silicon or metal surfaces, further blurring their
distinction. A pair of the team's scientists - Michel Baudry, a
professor of biological sciences, and Roberta Brinton, an
associate professor of molecular pharmacology - have begun
developing such cultures with animal tissue. When their research
is finalized, says Berger, "We will have created a physical
connection, or synapses, between the brain cells and computer
chips. We have the basic ingredients for a brain replacement."
The most remarkable aspect of all, says fellow team member
Tanguay, is that such a device represents the sheer oddity of
today's science. Increasingly, researchers are able to find
solutions without fully understanding the underlying process. "We
may never really know how the brain works, but we might be able to
understand enough about how neurons correlate and work together to
run the mathematical model," he explains. "By connecting a silicon
neural circuit to a probe chip and allowing it to 'learn' and then
feed data back, it's possible to diagnose and fix the problem
without having a clue how the system achieved the results. The
brain would use its natural adaptive abilities to reestablish all
the correct connections."
In other words, the device could learn the brain's native language
and speak it, but not interpret it to the outside world.
The research is also yielding data that can be plugged into an
array of other, seemingly divergent, scientific disciplines. Says
Joel Davis, program manager at the Office of Naval Research: "Once
you understand the algorithms that drive the brain, you can apply
them to all sorts of real-world problems that require computing.
You can use reverse engineering to solve problems in
communications, sonar, and neural networks."
One spin-off has been a new type of parallel-processing network
that could dramatically improve the quality of wireless and
cellular communication. By embedding an existing algorithm in a
microchip that mimics a biological model, it is possible to
drastically reduce the effects of noise and distortion. Yet
another prototype design, which used the same biological
processing model, promises to improve speech recognition.
Of course, connecting all the dots on the brain implant remains
the team's central focus - and their enormous challenge. For one
thing, there's a dizzying array of experimental technologies that
must intertwine and complement one another perfectly. It's one
thing to create computer simulations onscreen in a highly
controlled environment, but it's quite another to make them work
in the real world of chemistry, biology, and neurophysiology.
Stimulating a neuron or two in the brain is a pretty good
achievement but mere child's play compared with stimulating
thousands of neurons and running electrical channels through each.
Then there's the profound question of how many artificial neurons
scientists can fit on a microchip, and how many chips they can
pack into a cranium. "The ever present scaling issue," as Tanguay
puts it. Even the simplest prototype versions of the device will
require far more exotic and sophisticated chips and
interconnections than the group has so far managed to design and
build. Alas, there's also the humbling reality that if any member
of the highly skilled research team drops out or dies, the project
could quickly crumble. So far, the team has steered remarkably
clear of ego and turf battles, but the irony remains inescapable -
the development of what could be the most advanced
parallel-processing network on earth hinges on the most basic and
tenuous: fellow humans.
Berger believes the team is about five years away from designing a
brain implant for animals and about 10 to 15 years away from the
first device for humans. With custom microchip designs taking
weeks or months and other technical hurdles at every turn, it's
certainly not a project for anyone with less than the patience of
Buddha and the persistence of someone who sells insurance.
That suits Berger just fine. Nobody ever said that building an
electronic brain would be easy, and it's clear that he's just as
infatuated with the process as with the thought of changing
people's minds."You build it neuron by neuron and chip by chip,"
he says. "You enjoy each experiment and piece of the puzzle while
keeping a focus on the bigger picture." Berger won't rest until he
has built a bionic brain. He definitely wants to get inside your
head.
Samuel Greengard(
[email protected]) is a Burbank, California
writer specializing in science and technology.
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