A fully implantable and rechargeable wireless brain sensor capable of relaying real-time broadband signals from up to 100 neurons in freely moving subjects was developed by engineers at Brown University.
Several copies of the novel low-power device have been performing well in animal models for more than year, a first in the brain-computer interface field. Brain-computer interfaces could help people with severe paralysis 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," said Arto Nurmikko, professor of engineering at Brown University 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.
Meanwhile, wired systems using similar implantable sensing electrodes are being investigated in brain-computer interface 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.
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.
In the 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.
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 - a "brain radio." All the wireless and charging signals pass through an electromagnetically transparent sapphire window.
In all, the device looks like a miniature sardine can with a porthole.
But what the team has packed inside makes it a major advance among brain-machine interfaces, said lead author David Borton, a former Brown graduate student and postdoctoral research associate who is now at Ecole Polytechnique Federale Lausanne in Switzerland.
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.
"The device uses less than 100 milliwatts of power, a key figure of merit," Nurmikko said.
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.
Borton is now 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.
Nurmikko is presenting their work this week at the 2013 International Workshop on Clinical Brain-Machine Interface Systems in Houston.
It has also been described in the Journal of Neural Engineering.