In a breakthrough that could change the future of neurotechnology, scientists have developed a brain implant smaller than a grain of rice. The device, known as a microscale optoelectronic untethered electrode (MOTE), is much smaller than existing implants and can be adapted to work in other delicate parts of the body.
“To our knowledge, 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.
About the width of a human hair – about 300 microns long and 70 microns wide – the implant works by encoding nerve signals into pulses of infrared light, which then travel through brain tissue and bone to the receiver. Molnar first conceived the concept in 2001; it took nearly two decades to accomplish this.
MOTE, designed using a gallium arsenide semiconductor diode, can emit light for data transmission and harvest light energy for power. The system uses the same transmission methods as standard microchips, using an optical encoder and a low-noise amplifier. Data is transmitted using pulse position modulation, which is also used in satellite optical communications.
Molnar emphasized that the implant can successfully transmit data while consuming very little electricity.
The device was first tested on cell cultures grown in the laboratory before being implanted into the cerebral cortex of mice – the area of the brain responsible for processing sensory signals from the whiskers. MOTE continuously recorded brain activity and synaptic patterns for over a year in both active and healthy mice.
One of the main problems with existing brain implants is their incompatibility with electrical monitoring techniques such as MRI. MOTE, however, is made of materials that eliminate this limitation. Its wireless design also solves another persistent problem – the irritation and immune reactions caused by traditional electrodes and optical fibers.
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“One of the motivations for this 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 disruption, but still capture brain activity faster than imaging systems, and without the need to genetically modify neurons for imaging,” explained Molnar.
In addition to brain monitoring, potential applications of MOTE extend to other sensitive areas such as the spinal cord. Molnar’s team believes his design could be integrated into synthetic skull plates or adapted to record signals from different tissues.
“Our technology provides the basis for accessing a wide range of physiological signals with small and untethered instruments implanted on chronic timescales,” the study authors concluded.
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