A neural implant the size of a grain of salt can record and wirelessly transmit brain activity for long periods of time.
A research team led by scientists from Cornell University in the United States has developed an extremely small neural implant, smaller than a grain of salt, capable of wirelessly transmitting brain activity data from a living animal for more than a year.
The achievement, published in the journal Nature Electronics, shows that microelectronic systems can operate and deliver advanced functions on a much smaller scale than was previously thought possible. This breakthrough opens the way for new approaches to long-term monitoring of neural activity using bio-integrated sensors and related technologies.
Extreme miniaturization of neural implants
The device, known as a microscale optoelectronic wireless electrode or MOTE, is powered by red and infrared laser light that can safely pass through brain tissue. It sends information back by emitting brief pulses of infrared light that carry encoded electrical signals from the brain.
A semiconductor diode made of aluminum gallium arsenide collects the incoming light to power the circuit while simultaneously generating the outgoing signal. The system is supported by a low-noise amplifier and an optical encoder, both fabricated using the same semiconductor technology commonly used in modern microchips.
The MOTE is approximately 300 micrometers long and 70 micrometers wide. “To our knowledge, this is the smallest neural implant capable of measuring electrical activity in the brain and transmitting it wirelessly. By using pulse-position modulation for encoding—the same code used, for example, in satellite optical communications—we can consume extremely little power for communication while still successfully receiving the data optically,” the researchers report.
New possibilities for monitoring the brain and the body
The researchers first tested the MOTE in cell cultures and then implanted it in the barrel cortex of mouse brains, the region that processes sensory information from whiskers. Over the course of a year, the implant successfully recorded spikes of electrical activity from neurons as well as broader patterns of synaptic activity, while the mice remained healthy and active.
“One of the motivations for this work is that traditional electrodes and optical fibers can irritate the brain. Tissue moves around the implant and can trigger an immune response. Our goal was to make the device small enough to minimize this disruption, while at the same time recording brain activity faster than imaging systems and without requiring genetic modification of neurons,” says Alyosha Molnar, professor at Cornell’s School of Electrical and Computer Engineering.
Molnar notes that the material composition of the MOTE could allow electrical recordings from the brain during MRI scans—something that is currently largely impractical with existing implants. The technology could also be adapted for use in other tissues, such as the spinal cord, and even combined with future innovations, such as optoelectronics embedded in artificial cranial plates.