Engineers at Brown University in the United States of America have developed a novel wireless, broadband, rechargeable and fully implantable brain sensor that has performed well when tested more than a year with animal models. This is a major breakthrough for brain-machine interfaces as described in the Journal of Neural Engineering. The brain sensor is capable of relaying real-time broadband signals from up to 100 neurons in a freely moving object. This breakthrough could help patients with severe paralysis to control devices with their thoughts.
“This has features that are somewhat akin to a cell phone, except the conversation that is being sent out is the brain talking wirelessly,” According to Arto Nurmikko, a Professor of Engineering at Brown University who supervised the device’s invention.
The advantage of the device is that Neuroscientists can now use it to observe, record, and analyze the signals the neutrons that is emitted by the part of the animal model’s brain. This wireless system addresses a major need for the next step in providing a practical brain-computer interface,” said neuroscientist John Donoghue, the Wriston Professor of Neuroscience at Brown University and director of the Brown Institute for Brain Science.
According to lead author David Borton, a former Brown graduate student and postdoctoral research associate who is now at Ecole Polytechnique Federale Lausanne in Switzerland “what the team has packed inside makes it a major advance among brain-machine interfaces”. He said the device that lloks like a miniature sardine can with a porthole contains 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.” The can measures 2.2 inches (56 mm) long, 1.65 inches (42 mm) wide, and 0.35 inches (9 mm) 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 the brain radio. All the wireless and charging signals pass through an electromagnetically transparent sapphire window.
“What makes the achievement discussed in this paper unique is how it integrated many individual innovations into a complete system with potential for neuroscientific gain greater than the sum of its parts,” Borton said. “Most importantly, we show the first fully implanted neural interface microsystem operated wirelessly for more than 12 months in large animal models — a milestone for potential [human] clinical translation.”
“The device uses less than 100 milliwatts of power, a key figure of merit, and 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” Nurmikko said.
Co-author Ming Yin, 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.
According to him “We tried to make the best tradeoff between the critical specifications of the device, such as power consumption, noise performance, wireless bandwidth and operational range,” Yin said. “Another major challenge we encountered was to integrate and assemble all the electronics of the device into a miniaturized package that provides long-term hermeticity (water-proofing) and biocompatibility as well as transparency to the wireless data, power, and on-off switch signals.”
With early contributions by electrical engineer William Patterson at Brown, 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.
The team worked closely with neurosurgeons to implant the device in three pigs and three rhesus macaque monkeys; but 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. If neuroscientists want to observe the brain signals produced during some running or foraging behaviors, for instance, they can’t use a cabled sensor to study how neural circuits would form those plans for action and execution or strategize in decision making.
The new wireless device is not approved for use in humans and is not used in clinical trials of brain-computer interfaces. It was designed, however, with that translational motivation. But according to Nurmikko “This was conceived very much in concert with the larger BrainGate team, affiliated with the Brown Institute for Brain Science including neurosurgeons and neurologists giving us advice as to what were appropriate strategies for eventual clinical applications,”
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.