A team of neuroengineers at Brown University, Providence, Rhode Island, have developed a wireless, broadband, rechargeable, fully implantable brain sensor that is capable of relaying real-time broadband signals from up to 100 neurons in freely moving subjects. Several copies of this device have been performing well in three pigs and three rhesus macaque monkeys for more than a year-something that the team said is a first in the brain-computer interface (BCI) field. The wireless BCI has implications for use in advanced prosthetics and robotic assistive devices, and could ultimately translate to significant advances that can also inform human neuroscience.
The results are described in the April issue of the Journal of Neural Engineering.
Engineers Nurmikko and Yin examine their prototype wireless, broadband neural-sensing device. Photograph by Fred Field, courtesy of Brown University.
“This has features that are somewhat akin to a cell phone, except the conversation that is being sent out is the brain talking wirelessly,” said Arto Nurmikko, PhD, the L. Herbert Ballou University professor of engineering and physics at Brown, who oversaw the device’s invention.
Neuroscientists can use such a device to observe, record, and analyze the signals emitted by scores of neurons in particular parts of the animal model’s brain. The value of wireless transmission is that it frees subjects to move however they intend, allowing them to produce a wider variety of more realistic behaviors. Meanwhile, wired systems using similar implantable sensing electrodes are being investigated in BCI research to assess the feasibility of people with severe paralysis moving assistive devices like robotic arms or computer cursors by thinking about moving their arms and hands.
In the two-part device, a pill-sized chip of electrodes implanted on the cortex sends signals through uniquely designed electrical connections into the device’s laser-welded, hermetically sealed titanium “can,” which is implanted below the skin. The can measures 2.2 inches (56mm) long, 1.65 inches (42mm) wide, and 0.35 inches (9mm) thick. That small volume houses an entire signal-processing system: a lithium ion battery, ultralow-power integrated circuits designed at Brown for signal processing and conversion, wireless radio and infrared transmitters, and a copper coil for recharging. All the wireless and charging signals pass through an electromagnetically transparent sapphire window. The device transmits data at 24 Mbps via 3.2 and 3.8 Ghz microwave frequencies to an external receiver. After a two-hour charge, delivered wirelessly through the scalp via induction, it can operate for more than six hours.
Co-author Ming Yin, PhD, a Brown postdoctoral scholar and electrical engineer, said one of the major challenges that the team overcame in building the device was optimizing its performance given the requirements that the implant device be small, low-power, and leak-proof, potentially for decades. Yin helped to design the custom chips for converting neural signals into digital data. The conversion has to be done within the device, because brain signals are not produced in the ones and zeros of computer data.
For the experiments outlined in the study, the device was connected to one array of 100 cortical electrodes, the microscale individual neural listening posts, but the new device design allows for multiple arrays to be connected, Nurmikko said. That would allow scientists to observe ensembles of neurons in multiple related areas of a brain network.
The new wireless device is not approved for use in humans and is not used in BCI clinical trials. It was designed, however, with that translational motivation.
“This was conceived very much in concert with the larger BrainGate team, including neurosurgeons and neurologists giving us advice as to what were appropriate strategies for eventual clinical applications,” said Nurmikko, who is also affiliated with the Brown Institute for Brain Science.
Lead author David Borton, PhD, a former Brown graduate student and postdoctoral research associate who is now at École Polytechnique Fédérale de Lausanne (EPFL), Switzerland, is spearheading the development of a collaboration between EPFL and Brown to use a version of the device to study the role of the motor cortex in an animal model of Parkinson’s disease. Meanwhile the Brown team is continuing work on advancing the device for even larger amounts of neural data transmission, reducing its size even further, and improving other aspects of the device’s safety and reliability so that it can someday be considered for clinical application in people with movement disabilities.
Editor’s note: This story was adapted from materials provided by Brown University.
