Like a well-guarded fortress, the human brain attacks intruders on sight. Foreign objects, including neural probes used to study and treat the brain, do not last long. But now, researchers have designed a probe that looks, acts, and feels so much like a real neuron that the brain cannot identify it as an imposter. According to Charles M. Lieber, this breakthrough “literally blurs the ever-present and clear dissimilarities in properties between man-made and living systems” — in other words, between human and machine.
Lieber, the Joshua and Beth Friedman University Professor at Harvard, and his lab members are authors on a new paper published in Nature Materials that presents a bioinspired design for neural probes. Implanted directly into brain tissue, the probes are designed to survive as long as possible in the organ’s warm, humid, inhospitable environment. Sensors hidden within protective casings send data back to researchers about how and when individual neurons fire and neural circuits communicate. This information could help scientists treat neurological disorders like Parkinson’s, reverse neural decay from Alzheimer’s and aging, and even enhance cognitive capabilities.
But current implants cannot trick the brain — they cause a foreign-body response. Large and stiff compared with real neurons and neural tissue, traditional implants have two major impediments to sustained monitoring. During the initial placement in brain tissue — which usually requires surgery — neurons flee the impacted area. Previous studies have shown that the brain’s immune system senses the foreign object and gets to work, causing inflammation and scar tissue to isolate the device. Even if they can capture signals beyond the scar tissue, rigid probes can shift position and end up replacing one neural signal for another, closer one.
“This will ultimately make the recorded signal unstable,” said first author Xiao Yang, a fourth-year graduate student in the Lieber lab. She moved her cupped hands together, then apart, then together again as she explained how she and her team built a probe that inspires a negligible immune response, records neural signals within a day post-implantation, and may even encourage tissue regeneration.
“The stereotype of the neural probe is that they are giant compared to the neuron targets that they’re interrogating,” she explained. “But in our case, they are essentially the same.” The team’s probe mimics three features that have previously been impossible to achieve in a lab: the shape, size, and flexibility of an actual neuron.
