The brain implant was created to rely on a semiconductor diode made from aluminium gallium arsenide. It can both emit light to transmit data and capture light energy for power due to this substance. (Image: Cornell University)
In a breakthrough that could reshape the future of neurotechnology, scientists have developed a brain implant smaller than a grain of rice. The device, known as a microscale optoelectronic tetherless electrode (MOTE), is significantly tinier than existing implants and can be adapted to function in other delicate parts of the body.
“As far as we know, this is the smallest neural implant that can measure electrical activity in the brain and transmit it wirelessly,” said co-author Alyosha Molnar, an electrical engineer at Cornell University.
Roughly the width of a human hair—about 300 microns long and 70 microns wide—the implant works by encoding neural signals into pulses of infrared light, which then travel through brain tissue and bone to a receiver. Molnar first conceived the concept in 2001; it took nearly two decades to bring it to reality.
Developed using a semiconductor diode made of aluminium gallium arsenide, MOTE can both emit light to transmit data and harvest light energy for power. The system uses the same transmission methods as standard microchips, aided by an optical encoder and a low-noise amplifier. Data is sent using pulse position modulation, a technique also used in satellite optical communication.
Molnar highlighted that the implant can successfully transmit data while consuming very little electricity.
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The device was first tested in lab-grown cell cultures before being implanted in the barrel cortex of mice—a brain region responsible for processing sensory input from whiskers. MOTE consistently recorded brain activity and synaptic patterns for over a year in both active and healthy mice.
One of the main challenges with existing brain implants is their incompatibility with electrical monitoring methods such as MRI scans. MOTE, however, is made from materials that eliminate this limitation. Its wireless design also addresses another persistent issue—irritation and immune responses triggered by traditional electrodes and optical fibres.
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“One of the motivations for doing this is that traditional electrodes and optical fibres can irritate the brain. The tissue moves around the implant and can trigger an immune response. Our goal was to make the device small enough to minimise disruption while still capturing brain activity faster than imaging systems, and without needing to genetically modify neurons for imaging,” Molnar explained.
Beyond brain monitoring, MOTE’s potential applications extend to other sensitive areas such as the spinal cord. Molnar’s team believes its design could be integrated into synthetic skull plates or adapted to record signals from various tissues.
“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.
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