Detecting Brain Chemicals

A new device could help with deep brain stimulation.

Deep brain stimulation (DBS), in which implanted electrodes deliver electric jolts to the brain, has shown great promise in treating neurological disorders: it is already approved to treat Parkinson's disease and is being tested to treat severe depression, obsessive-compulsive disorder, traumatic brain injury, and other ailments. But despite its success, little is known about how DBS works. Scientists at the Mayo Clinic and other institutions have developed a new device that can detect neurotransmitters quickly and locally in the brain, which they hope will help make DBS more effective and shed light on how it works.

Sampling the brain: A device by the Mayo Clinic can analyze and detect neurotransmitters locally in the brain. Blue wires link an external monitor (circuit board) to gray connectors, which are in turn linked to neurotransmitter-sensing electrodes (not shown). The device is battery operated (the battery is shown connected to the circuit board) and can transmit the neurochemical information from the electrodes to a remote station for analysis. Credit: Division of Engineering at the Mayo Clinic

Patients undergoing DBS are surgically implanted with an electrode, which is connected to a stimulator implanted under the skin. The electrode delivers a tightly controlled series of electrical pulses to a specific part of the brain, but the physiological changes that it triggers are not well understood. Scientists theorize that these jolts either activate sluggish or diseased neural circuits, or interfere with abnormal electrical messages. Many of the parameters of the treatment, such as the place that the electrode is inserted and the magnitude and frequency of the electrical signals that it emits, have been optimized by trial and error.

"There is no standard technique by which we can sample the brain regions in patients as we're implanting the deep brain stimulation systems," says Ali Rezai, director of the Center for Neurological Restoration at the Cleveland Clinic, who was not involved in the current study but performs DBS procedures. "In the future, this [device] may be a way of helping improve DBS surgeries and guiding us for improving the outcome of these patients."

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The new device, developed by scientists at the Mayo Clinic Neural Engineering laboratory,consists of a sensor electrode that can be implanted along with the DBS electrode and detects the concentration of chemical messengers, called neurotransmitters, that are released from neurons. The sensor is attached to an external controller, which analyzes the signals and wirelessly sends the data to a remote laptop for further analysis. "This is a powerful device that, in real time, can do the analysis of neurotransmitter changes in the brain," says Kendall Lee, director of the Mayo Clinic Neural Engineering laboratory, who directs the work.

The researchers are focusing first on Parkinson's disease, which is characterized by damage to neurons that produce the neurotransmitter dopamine. "We think that deep brain stimulation could be treating symptoms of Parkinson's disease, at least in part, by activating surviving dopamine neurons," says Paul Garris, a professor of neurobiology at Illinois State University, who works on the project. "We want to take this surgical procedure to the next step and use the chemical recording to fine-tune the position of the stimulating electrode to release the most robust dopamine."