Stimulating nerve cells with laser precision; Researchers devise optical method to safely, effectively stimulate neurons

Nashville, Tenn. ñ Biomedical engineers and physicians at Vanderbilt
University have brought the day when artificial limbs will be
controlled directly by the brain considerably closer by discovering a
method that uses laser light, rather than electricity, to stimulate and
control nerve cells.

The researchers have discovered that low-intensity infrared laser light
can spark specific nerves to life, exciting a leg or even individual
toes without actually touching the nerve cells.

"This technique brings nerve stimulation out of the Dark Ages," said
Vanderbilt Assistant Professor of Biomedical Engineering and
Neurological Surgery Anita Mahadevan-Jansen. "Much work is going on
around the world trying to make electric nerve stimulation better, but
the technique is inherently limited. Using lasers instead, we can
simultaneously excite and record the responses of nerve fibers with
much greater precision, accuracy and effectiveness."

The method was developed by Mahadevan-Jansen; her husband Duco Jansen,
associate professor of biomedical engineering and neurological surgery;
Dr. Peter Konrad and Dr. Chris Kao of Vanderbilt Neurological Surgery,
both assistant professors of neurological surgery; and biomedical
engineering doctoral student Jonathon Wells.

In an experiment with rats, the scientists used a laser to stimulate
the sciatic nerve and to control muscles in the animal’s hind leg and
individual toes, demonstrating accuracy beyond the limitations of
electrical stimulation. Immediately following the experiment, the rats
regained full use of their legs with no signs of weakness or damage.

Konrad, who is also director of the Vanderbilt Functional Neurosurgery
program, points out that neurostimulation is ideally done cell by cell.
"The problem with the conventional electrical method is that we have a
large zone around our target neuron that also is affected simply
because of the way electricity travels throughout the tissue. Using
light to stimulate neurons, we can pick off a single neuron without
affecting the other neurons around it."

In a matter of months, Kao says, a machine could be created that helps
guide neurosurgeons to the target nerves during rhizotomy, a procedure
that frees someone from a spastic or seemingly frozen muscle, as when
someone’s head is stuck in a tortuous position. Currently, once the
proper neural region is selected, surgeons pinpoint the individual
nerves by a process of elimination, striking nerves with an electric
probe while the patient is awake to ensure that the right nerve has
been located.

But electrical probes create a halo of electrical activity in
surrounding neurons, creating a "blind spot" and other inaccurate data
in the recording and analysis of the procedure, making it tedious and
difficult to locate the exact nerve.

Optics, on the other hand, can deliver laser precision by stimulating only the nerve cell of interest.

The idea of optical stimulation started as the scientists questioned
whether they could accurately detect the movement through the brain of
an electrical impulse from a nerve cell. Konrad suggested using light
to trace the activity, and Mahadevan-Jansen thought of using laser
light to stimulate nerves and to actually generate this activity.

Vanderbilt’s W.M. Keck Foundation Free Electron Laser Center was the
perfect facility to give it a try. The Department of Defense-funded
FEL, one of only a handful in the world and the only one equipped to
perform medical experimental research, was used to see if the idea
worked and to determine the optimal settings for the laser.

Now that the research team has shown that the process works and that it
is safe, they are turning their attention to studying the exact
mechanisms behind the stimulation effects. The most likely candidates,
Jansen and Wells say, include a photothermal or mechanical effect or
perhaps a combination of the two.

The scientists are beginning experiments in the central nervous system.

Mahadevan-Jansen said the technique, which is pending patent approval,
is not the only novel aspect of this work. "This research results from
the marriage of biomedical engineering, optical science and
neurological research," Mahadevan-Jansen said. "Some programs are
working on optics, and some are working on neurological stimulation,
but nobody has put them together."

Imagining future applications, Konrad said he can envision an array of
fiber optic threads that runs directly from the brain or spinal cord to
a prosthetic arm or leg, creating the ultimate man-machine interface.


Media contacts: Vivian Cooper-Capps, (615) 322-2762

Clinton Colmenares, (615) 322-4747

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