Global Research, July 09, 2015
Nature 8 June 2015
Region: USA
Theme: Science and Medicine
Electronic mesh has potential to
unravel workings of mammalian brain.
This soft, conductive polymer mesh
can be rolled up and injected into the brains of mice.
A simple injection is now all it
takes to wire up a brain. A diverse team of physicists, neuroscientists and
chemists has implanted mouse brains with a rolled-up, silky mesh studded with
tiny electronic devices, and shown that it unfurls to spy on and stimulate
individual neurons.
The implant has the potential to
unravel the workings of the mammalian brain in unprecedented detail. “I think
it’s great, a very creative new approach to the problem of recording from large
number of neurons in the brain,” says Rafael Yuste, director of the Neurotechnology
Center at Columbia University in New York, who was not involved in the work.
Lieber Research Group, Harvard
University
If eventually shown to be safe, the
soft mesh might even be used in humans to treat conditions such as Parkinson’s
disease, says Charles Lieber, a chemist at Harvard University on Cambridge,
Massachusetts, who led the team. The work was published inNature
Nanotechnology on 8 June1.
Neuroscientists still do not
understand how the activities of individual brain cells translate to higher
cognitive powers such as perception and emotion. The problem has spurred a hunt
for technologies that will allow scientists to study thousands, or ideally
millions, of neurons at once, but the use of brain implants is currently
limited by several disadvantages. So far, even the best technologies have been
composed of relatively rigid electronics that act like sandpaper on delicate
neurons. They also struggle to track the same neuron over a long period,
because individual cells move when an animal breathes or its heart beats.
The Harvard team solved these
problems by using a mesh of conductive polymer threads with either nanoscale
electrodes or transistors attached at their intersections. Each strand is as
soft as silk and as flexible as brain tissue itself. Free space makes up 95% of
the mesh, allowing cells to arrange themselves around it.
In 2012, the team showed2 that living cells grown in a dish
can be coaxed to grow around these flexible scaffolds and meld with them, but
this ‘cyborg’ tissue was created outside a living body. “The problem is, how do
you get that into an existing brain?” says Lieber.
The team’s answer was to tightly
roll up a 2D mesh a few centimetres wide and then use a needle just
100 micrometres in diameter to inject it directly into a target region
through a hole in the top of the skull. The mesh unrolls to fill any small
cavities and mingles with the tissue (see ‘Bugging the brain’). Nanowires that poke out can
be connected to a computer to take recordings and stimulate cells.
So far, the researchers have
implanted meshes consisting of 16 electrical elements into two brain
regions of anaesthetized mice, where they were able to both monitor and
stimulate individual neurons. The mesh integrates tightly with the neural cells,
says Jia Liu, a member of the Harvard team, with no signs of an elevated immune
response after five weeks. Neurons “look at this polymer network as friendly,
like a scaffold”, he says.
The next steps will be to implant
larger meshes containing hundreds of devices, with different kinds of sensors,
and to record activity in mice that are awake, either by fixing their heads in
place, or by developing wireless technologies that would record from neurons as
the animals moved freely. The team would also like to inject the device into
the brains of newborn mice, where it would unfold further as the brain grew,
and to add hairpin-shaped nanowire probes to the mesh to record electrical
activity inside and outside cells.
When Lieber presented the work at a
conference in 2014, it “left a few of us with our jaws dropping”, says Yuste.
There is huge potential for
techniques that can study the activity of large numbers of neurons for a long
period of time with only minimal damage, says Jens Schouenborg, head of the
Neuronano Research Centre at Lund University in Sweden, who has developed a
gelatin-based ‘needle’ for delivering electrodes to the brain3. But he remains sceptical of this
technique: “I would like to see more evidence of the implant’s long-term
compatibility with the body,” he says. Rigorous testing would be needed before
such a device could be implanted in people. But, says Lieber, it could
potentially treat brain damage caused by a stroke, as well as Parkinson’s
disease.
Lieber’s team is not funded by the
US government’s US$4.5-billion Brain Research through Advancing Innovative
Neurotechnologies (BRAIN) initiative, launched in 2013, but the work points to
the power of that effort’s multidisciplinary approach, says Yuste, who was an
early proponent of the BRAIN initiative. Bringing physical scientists into
neuroscience, he says, could help to “break through the major experimental and
theoretical challenges that we have to conquer in order to understand how the
brain works”.
Nature 522, 137–138 (11 June 2015) doi:10.1038/522137a
References
1) Liu, J. et al. Nature
Nanotechnol. http://dx.doi.org/10.1038/nnano.2015.115 (2015).
2) Tian, B. et al. Nature
Mater. 11, 986–994 (2012).
3) Lind, G., Linsmeier, C.
E., Thelin, J. & Schouenborg, J. J. Neural
Eng. 7, 046005 (2010). Article
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