Today’s neural implants are smaller than ever, but often remain cumbersome and prone to complications. According to researchers at Cornell University, a new iteration detailed this week in the journal Nature Electronics may offer a novel path forward for brain implants. Small enough to fit on a grain of rice, the microscale optoelectronic tetherless electrode (or MOTE) is vastly smaller than similar implants and its design could be adapted to work in other delicate areas of the body.
“As far as we know, this is the smallest neural implant that will measure electrical activity in the brain and then report it out wirelessly,” electrical engineer and study co-author Alyosha Molnar said in a statement.
MOTE measures only 300 microns long and 70 microns wide, or about the width of a single human hair. It works by encoding neural signals within small pulses of infrared light, before sending the information harmlessly through brain tissue and bone to a receiver. Although Molnar first envisioned an early iteration of MOTE in 2001, it would take over two decades before the project truly got off the ground.
He and collaborators designed the implant to rely on a semiconductor diode made from aluminum gallium arsenide. This material enables it to harvest light energy for power while also emitting light to send data. The diode is supported with a low-noise amplifier and optical encoder using the same transmission principles seen in standard microchips. Data transmission is accomplished through pulse position modulation–the same technology seen in many satellite optical communications arrays.
“We can use very, very little power to communicate and still successfully get the data back out optically,” explained Molnar.
The team initially tested MOTE in lab-grown cell cultures before moving onto mice. For trials, they implanted the device in the rodent’s barrel cortex, the region of the brain evolved to process sensory input from whiskers. For over a year, MOTE reliably recorded neural activity spikes along with wider synaptic activities with both active and healthy mice.
One major drawback to most current brain implants is that they cannot function when a patient undergoes electrical monitoring like during an MRI. However, MOTE is made from materials that allow it to bypass this issue entirely. Its wireless capabilities also solve another recurring issue for implants.
“One of the motivations for doing this is that traditional electrodes and optical fibers can irritate the brain. The tissue moves around the implant and can trigger an immune response,” said Molnar. “Our goal was to make the device small enough to minimize the disruption while still capturing brain activity faster than imaging systems, and without the need to genetically modify the neurons for imaging.”
The implications go beyond brain monitoring. Molnar’s team is confident that MOTE’s underlying design can allow it to be adapted for other tissues, even in regions as sensitive as the spinal cord. It may also have uses if embedded inside artificial skull plates.
“Our technology provides the basis for accessing a wide variety of physiological signals with small and untethered instrumentation implanted on chronic timescales,” the study’s authors concluded.
2025 Holiday Gift Guide
