MEMS Magnetic Sensing and Stimulating Brain Implants

A transdisciplinary team of neuroscientists and engineers at Penn State is developing MEMS (microelectromechanical systems) tech to monitor and stimulate neural electric signals— without invasive brain implants.

Led by Dr. Srinivas Tadigadapa (professor of electrical engineering) and Dr. Steven Schiff (director of the Penn State Center for Neural Engineering), the Penn State team aims to create a device that can be implanted inside the skull without needing to conduct brain surgery for implantation.

Dr. Tadigadapa (left) and Dr. Schiff (right). Image courtesy of Penn State. 

Implants in the Brain vs. Skull

The team has set its sights on magnetic stimulation of neurons compared to electrical stimulation.
Traditionally, electrical stimulation via implant has required piercing the dura of the brain— the outermost layer of the protective membrane that surrounds the brain and spinal cord.

The meninges protecting the brain and spinal cord. The dura is the outermost layer. Image courtesy of NIH.gov.

As with any surgery, placing implants within the dura comes with a host of dangers. Besides the risk of infection inherent in surgery, there’s also the danger of scarring in the brain. Brain scarring around these implants can cause them to function incorrectly, requiring yet more surgery to remove the scarred tissue in a dangerous cycle.
Tadigadapa and Schiff’s research aims to sidestep the dangers that come with placing implants within the dura. Instead, they hope to implant their technology within the skull but outside of the brain entirely.

Micro-Magnetic Coils

Transcranial Magnetic Stimulation (TMS) is a method of using large-scale magnetic coils (described as “fist-sized”) to activate large portions of the brain through the skull.
Tadigadapa aims to use this approach, but with much more precision— stimulating the brain with neuron-level specificity. But neuron-level specificity requires the use of much smaller magnetic coils.

Micro-magnetic coils. Image courtesy of Penn State. 

According to Eugene Freeman, a Ph.D. candidate working with Dr. Tadigadapa on the issue of developing these smaller coils, they’re making serious progress in shrinking the tech down. The smallest coils they’ve made so far is close to 500 microns in diameter (which he compares to half a grain of salt). The coils are made out of microglass with 3D copper coils patterned on them.

Using Microchips to Counter the Earth’s Magnetic Field

One of the major challenges facing Tadigadapa’s work is interference from the earth’s magnetic field. The brain generates a magnetic field that measures about one picoTesla. By comparison, at its surface the earth’s magnetic field measures between 25 and 65 microTeslas (between 25 to 65 million times stronger than a brain’s picoTesla).
This means that any sensing or actuating the Penn State team aims to do on an individual neuron level must take the earth’s magnetic field into account.
Tadigadapa’s proposed solution? Use a CMOS microchip. The chip would use active and passive circuits to create a feedback loop capable of countering the “noise” of the earth’s magnetic field (and other interferences). Additionally, other circuits could be used to amplify a specific neuron’s electrical signals.

A MEMS chip. Image courtesy of Genome.gov.

If Tadigadapa’s team succeeds in developing such a chip, they could effectively avoid the multimillion dollar process that blocking the earth’s magnetic field currently requires. The process involves the use of a room specifically for electromagnetic isolation and the ever-present (and ever-expensive) challenge of needing to cool devices with liquid helium, which is necessary for current sensor technology.
To that end, the sensor tech Penn State is developing would be impressive in its own right for being able to function at ambient temperatures.

Applications and Timeline

Developing this technology has widespread uses. For one, with portable coils, it could become possible to do TMS therapy outside of a lab to treat depression and OCD.

Example of a TMS therapy coil in use. Image courtesy of the University of Washington.

The ability to have non-invasive sensor technology would also make brain-controlled prosthetics much easier to upkeep (as current techniques require implants below the dura, facing the host of issues and dangers discussed above).
Dr. Schiff, who has worked with epilepsy patients for much of his career, says that the technology could also allow for strides in treating epilepsy— both in sensing epileptic episodes and also possibly in preventing them.
The current hope is that there could be testing within five years. The earliest models are projected to be placed on the outside of the skull until the entire apparatus is compact enough to attempt putting inside the skull.

BRAIN Initiative

Tadigadapa and Schiff’s research is funded in part by the NIH’s BRAIN Initiative, which aims to support research into brain function and cognitive disorders. Learn more about the BRAIN Initiative here.