Implantable Chip Measures and Adjusts Dopamine Levels in Mouse Brain

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Illustration: iStockphoto

Researchers have created an implantable chip that detects and adjusts dopamine levels in mice brains by tracing the neurotransmitter itself rather than relying on electrical signals, as most brain implants do. When the levels drop below a defined point, the device automatically sends an electrical impulse to prod neurons to release more.

Pedram Mohseni, an electrical engineer at Case Western Reserve University who led the project, likens it to a home thermostat. “A thermostat basically monitors the temperature and it turns on or off to regulate the temperature,” he says. “Our device operates the same way.”

He hopes it can someday help patients with disorders related to skewed levels of neurotransmitters. For now, his team has shown that it can successfully record and adjust dopamine levels in a mouse brain.

In a healthy person, neurotransmitters are the reliable messengers that zip signals through the brain. But having too many or too few can cause problems. That’s why pharmacists dole out Prozac to boost serotonin and Ritalin to increase dopamine.

However, medicines remain an imperfect solution. Patients must remember to take them, and pills are a one-size-fits-all approach for disorders that often vary widely between patients.

For a more direct approach, Mohseni and his collaborators at Illinois State University invented a brain implant that uses a carbon fiber electrode to measure pH and the flow of dopamine nearby. A digital signal processing unit runs that information through an algorithm written to calculate changes in dopamine levels.

If levels dip below a certain point, the device sends an electrical signal to stimulate production. The device is currently programmed for dopamine, but Mohseni says its algorithm could be rewritten to track and adjust other neurotransmitters.

Harbaljit Sohal, a postdoc researcher in synthetic neurobiology at MIT, says that’s “a very useful approach.” Other methods of brain stimulation have used electrical impulses to detect neurological changes, but this chip’s electrode directly translates chemical signals such as pH into a precise reading of neurotransmitter production. Many of those previous methods also required manual adjustments to elevate or lower neurotrasmitter levels while the new device can automatically fine-tune them.

But Sohal expects it will be challenging to find a way to power the device and overcome interference caused by the human body’s tendency to react to implants.

Dr. Brian Kopell, director of the center for neuromodulation at Mt. Sinai Hospital in New York City, says demonstrating a successful closed-loop approach in a brain implant is an achievement, but it’s not clear whether detecting chemical signals will actually prove more efficient than electrical ones. “It’s a nifty study,” he says. “But it’s nothing that’s blowing my mind.”

For the time being, Mohseni’s dream of seeing his device used alongside medication to treat patients remains far off in the future. The group recently published a proof of concept of the device in which they implanted the device into a single rat to IEEE Transactions on Biomedical Circuits and Systems. Their next step will be to test it in many more animals including primates. Human trials may not take place for years.

Craig Berridge, a neurobiologist at University of Wisconsin-Madison, points out that this method only measures dopamine in real time, so wouldn’t help scientists track disorders linked to high or low levels of dopamine over a long period. “It's probably going to be most useful in animal studies where we're trying to understand the role of dopamine in various neural processes,” he says.

If it does make it to human trials, the device would also only be useful for disorders for which physicians can clearly define “healthy” versus “unhealthy” levels of dopamine or other neurotransmitters. Though researchers are getting closer to describing this “therapeutic window,” as Mohseni calls it, for Parkinson’s disease, their understanding is not nearly so advanced for other disorders. Addiction, for example, is far more difficult to define in this way.

Dr. Michele Tagliati, a neurologist at Cedars-Sinai Medical Center, adds that degenerative disorders such as Parkinson’s disease might not be a good fit either because the chip relies on its ability to stimulate healthy neurons to release dopamine.

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