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Brain Chip Combines Electrodes and Microfluidics

It’s the first to measure electrical and chemical signals together in a live animal

3 min read
Magnified image of a brain probe with a set of thin microfluidic channel lines that each end at a separate square intake port
Korea Institute of Science and Technology(KIST)

Neurons use electrical pulses and chemicals to communicate with each other. Analyzing both is critical for studying brain function and spotting brain diseases, but today’s implants can measure only one or the other.

Researchers in Korea have now made a multifunctional chip that can measure both electrical charges and neurochemicals in the brain, and can also inject drugs in real time. They tested the chip, which is smaller than a U.S. quarter-dollar coin, in live mice.

“I expect our novel technology to provide opportunities for a variety of studies for the in-depth study of brain functions as well as for the investigation of neural circuits related to brain diseases,” says Il-Joo Cho of the Korea Institute of Science and Technology’s Brain Science Institute.

Measuring the concentration of neurotransmitters, the chemicals that transmit signals between neurons, can give pivotal insights into brain function, Cho says. People with Parkinson’s disease, for instance, have lower levels of serotonin, dopamine, and other neurotransmitters than normal. And in schizophrenia, neurons that release dopamine are much more active than in a typical brain.

But measuring these neurotransmitter levels today requires inserting a probe with a fluidic channel into the brain to collect brain fluid, which is analyzed using techniques like spectroscopy. That’s slow, and the millimeter-wide probes can cause tissue damage.

Recording the brain’s electrical signals is more straightforward. It can be done using ultrathin flexible polymer-based neural probes implanted in target brain regions, or metal electrodes attached to the scalp.

Scientists over the years have built brain implants that can measure the brain’s electrical signals to predict epileptic seizures, measure pH to determine and adjust dopamine levels, and they've seen some success with small, electrically controlled, pump-like devices that rapidly deliver neurotransmitters to the brain where needed.

But devices that can simultaneously measure electrical and neurochemical signals are hard to come by. One group recently reported tiny MEMS-based sampling devices that can collect extracellular fluid without damaging tissue, but these devices cannot record electrical signals.

Deciphering the quantitative relationships between those two signals in vivo would be valuable for neuroscience studies, Cho says. For example, it would allow neuroscientists to investigate the effect of drugs on the activities of specific types of brain cells. This has previously only been possible by analyzing brain slices, he says.

Cho says theirs is the first device capable of measuring electrical and chemical signals from the same area of the brain in a live animal. The device has a probe patterned with an array of twelve electrodes for recording electrical signals, and two in-built microfluidic channels to collect brain fluid.

The probe is only 40 micrometers thick, and has a cross-sectional area that is one-third or even one-fourth the girth of previously made probes—which minimizes tissue damage during insertion into the brain. The device also has a microfluidic interface chip attached to the probe for delivering drugs to the site.

In experiments on live mice, Cho and his colleagues delivered drugs to modulate the neural circuits in a targeted brain region. They observed changes in electrical signals in real time, and measured neurotransmitter levels in brain fluid samples taken every 20 minutes.

When they injected a potassium chloride solution, which is known to excite neurons, electrical signals fired at a much faster rate and concentrations of two neurotransmitters also increased significantly. The opposite happened when they injected an inhibitory drug that is known to suppress neural circuits. The researchers presented their device and experimental results in the journal Biosensors and Bioelectronics.

Cho says that the team now plans to add a real-time neurotransmitter monitoring ability. That should let them assess the correlation between electrical and chemical signals in real time.

The Conversation (0)
Illustration showing an astronaut performing mechanical repairs to a satellite uses two extra mechanical arms that project from a backpack.

Extra limbs, controlled by wearable electrode patches that read and interpret neural signals from the user, could have innumerable uses, such as assisting on spacewalk missions to repair satellites.

Chris Philpot

What could you do with an extra limb? Consider a surgeon performing a delicate operation, one that needs her expertise and steady hands—all three of them. As her two biological hands manipulate surgical instruments, a third robotic limb that’s attached to her torso plays a supporting role. Or picture a construction worker who is thankful for his extra robotic hand as it braces the heavy beam he’s fastening into place with his other two hands. Imagine wearing an exoskeleton that would let you handle multiple objects simultaneously, like Spiderman’s Dr. Octopus. Or contemplate the out-there music a composer could write for a pianist who has 12 fingers to spread across the keyboard.

Such scenarios may seem like science fiction, but recent progress in robotics and neuroscience makes extra robotic limbs conceivable with today’s technology. Our research groups at Imperial College London and the University of Freiburg, in Germany, together with partners in the European project NIMA, are now working to figure out whether such augmentation can be realized in practice to extend human abilities. The main questions we’re tackling involve both neuroscience and neurotechnology: Is the human brain capable of controlling additional body parts as effectively as it controls biological parts? And if so, what neural signals can be used for this control?

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