A new method has been developed to stimulate brain tissue using external
magnetic fields and injected magnetic nanoparticles.
The technique allows direct stimulation of neurons, which could be an
effective treatment for a variety of neurological diseases, without the need
for implants or external connections.
The research, conducted by Polina Anikeeva, an assistant professor of
materials science and engineering, graduate student Ritchie Chen, and three
others, has been published in the journal Science.
Polina Anikeeva, an assistant professor of materials science, said that
previous efforts to stimulate the brain using pulses of electricity have proven
effective in reducing tremors associated with Parkinson's disease. However, the
treatment has remained a last resort as it requires highly invasive implanted
wires that connect to a power source outside the brain, he added.
"In the future, our technique may provide an implant-free means to
provide brain stimulation and mapping," Anikeeva says.
In their study, the research team injected magnetic iron oxide particles
just 22 nanometers in diameter into the brain. When exposed to an external
alternating magnetic field, these particles rapidly heat up.
The resulting local temperature increase can then lead to neural activation
by triggering heat-sensitive capsaicin receptors - the same proteins that the
body uses to detect both actual heat and the "heat" of spicy foods.
The team used viral gene delivery to induce the sensitivity to heat in selected
neurons in the brain.
The particles, which have virtually no interaction with biological tissues
except when heated, tend to remain where they're placed, allowing for long-term
treatment without the need for further invasive procedures.
"The nanoparticles integrate into the tissue and remain largely intact.
Then, that region can be stimulated at will by externally applying an
alternating magnetic field. The goal for us was to figure out whether we could
deliver stimuli to the nervous system in a wireless and noninvasive way,"
The new work has proven that the approach is feasible, but much work remains
to turn this proof-of-concept into a practical method for brain research or
The use of magnetic fields and injected particles has been an active area of
cancer research; the thought is that this approach could destroy cancer cells
by heating them.
"The new technique is derived, in part, from that research,"
Anikeeva says. "By calibrating the delivered thermal dosage, we can excite
neurons without killing them. The magnetic nanoparticles also have been used
for decades as contrast agents in MRI scans, so they are considered relatively
safe in the human body."
The team developed ways to make the particles with precisely controlled
sizes and shapes, in order to maximize their interaction with the applied
alternating magnetic field. They also developed devices to deliver the applied
magnetic field: Existing devices for cancer treatment -- intended to produce
much more intense heating -- were far too big and energy-inefficient for this
The research, an assistant professor of materials
science and engineering, graduate student Ritchie Chen, and three others, was
published in the journal Science.