IEEE Spectrum September, 2014 - 17

Lawrence LivermOre natiOnaL LaBOratOry

the medical device maker Medtronic, in
Minneapolis, which has already developed
one experimental implant that can both
record neural activity and stimulate the
brain. Researchers have long wanted such
a "closed-loop" device, as it can use realtime signals from the brain to define the
stimulation parameters.
Kahana notes that designing such
closed-loop systems poses a major engineering challenge. Recording natural
neural activity is difficult when stimulation introduces new electrical signals,
so the device must have special circuitry
that allows it to quickly switch between
the two functions. What's more, the recorded information must be interpreted
with blistering speed so it can be translated into a stimulation command. "We
need to take analyses that used to occupy
a personal computer for several hours and
boil them down to a 10-millisecond algorithm," he says.

rEMEMbEr thiS? Lawrence Livermore engineer
Vanessa Tolosa holds up a silicon wafer containing
micromachined implantable neural devices for use in
experimental memory prostheses.

In four years' time, Kahana hopes his
team can show that such systems reliably improve memory in patients who
are already undergoing brain surgery for
epilepsy or Parkinson's. That will lay the
groundwork for future experiments, he
says, in which medical researchers can try
out the hardware in people with traumatic
brain injuries, who would not normally
receive invasive neurosurgery.
The second research team is led by Itzhak
Fried, director of the Cognitive Neurophysiology Laboratory at the University
of California, Los Angeles. Fried's team
will focus on a part of the brain called the
entorhinal cortex, which is the gateway to
the hippocampus, the primary brain region
associated with memory formation and stor-

age. "Our approach to the RAM
program is homing in on this circuit, which is really the golden
circuit of memory," Fried says.
In a 2012 experiment, he showed
that stimulating the entorhinal
regions of patients while they
were learning memory tasks improved their performance.
Fried's group is working with
Lawrence Livermore National
Laboratory, in California, to develop more closed-loop hardware. At Livermore's Center for
Bioengineering, researchers are
leveraging semiconductor manufacturing techniques to make tiny
implantable systems. They first
print microelectrodes on a polymer that sits atop a silicon wafer,
then peel the polymer off and
mold it into flexible cylinders
about 1 millimeter in diameter.
The memory prosthesis will have
two of these cylindrical arrays,
each studded with up to 64 hairthin electrodes, which will be
capable of both recording the
activity of individual neurons and stimulating them. Fried believes his team's device
will be ready for tryout in patients with
traumatic brain injuries within the fouryear span of the RAM program.
Outside observers say the program's
goals are remarkably ambitious. Yet Steven
Hyman, director of psychiatric research
at the Broad Institute of MIT and Harvard,
applauds its reach. "The kind of hardware
that DARPA is interested in developing
would be an extraordinary advance for the
whole field," he says. Hyman says DARPA's
funding for device development fills a gap
in existing research. Pharmaceutical companies have found few new approaches to
treating psychiatric and neurodegenerative disorders in recent years, he notes,
and have therefore scaled back drug discovery efforts. "I think that approaches
that involve devices and neuromodulation
have greater near-term promise," he says.
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Table of Contents for the Digital Edition of IEEE Spectrum September, 2014