Understanding the anatomical structure and function of the brain is a longstanding goal in neuroscience. Electrical and optical techniques offer distinct and complementary advantages that, if used together, could offer profound benefits for studying the brain at high resolution. Combining these technologies is challenging, however, because conventional metal electrode technologies are too thick (>500nm) to be transparent to light, making them incompatible with many optical approaches. To help overcome these challenges, the Defense Advanced Research Projects Agency (DARPA) has created a proof-of-concept tool that demonstrates much smaller, transparent contacts that can measure and stimulate neural tissue using electrical and optical methods at the same time. This tool could be used to inform and improve neural interfaces, such as those used to control dexterous functions made possible with advanced prosthetic limbs.
Conventional metal electrode technologies (top left) are opaque, obstructing views of underlying neural tissue. The new graphene sensors developed by under the RE-NET program are electrically conductive but only four atoms thick (top middle). Placed on a flexible plastic backing that conforms to the shape of tissue (bottom), the sensors are part of a proof-of-concept tool that demonstrates much smaller, transparent contacts that can measure and stimulate neural tissue using electrical and optical methods at the same time (top right). Image courtesy of DARPA.
Researchers at the University of Wisconsin at Madison developed the new technology with support from DARPA’s Reliable Neural-Interface Technology (RE-NET) program. It is described in detail in a paper in Nature Communications. DARPA created the RE-NET program in 2010; RE-NET seeks to develop the technologies needed to reliably extract information from the nervous system, and to do so at a scale and rate necessary to control many degree-of-freedom (DOF) machines, such as high-performance prosthetic limbs.
The new device uses graphene, a recently discovered form of carbon, on a flexible plastic backing that conforms to the shape of tissue. The graphene sensors are electrically conductive but only four atoms thick. Its extreme thinness enables nearly all light to pass through across a wide range of wavelengths. Moreover, graphene is nontoxic to biological systems, an improvement over previous research into transparent electrical contacts that are much thicker, rigid, difficult to manufacture, and reliant on potentially toxic metal alloys.
RE-NET, and subsequent DARPA programs in this field, plan to leverage this new tool by simultaneously measuring the function, physical motion, and behavior of neurons in freely moving subjects. This technology provides the capability to modulate neural function by applying programmed pulses of electricity or light to temporarily activate neurons. Therefore, it could not only provide better observation of native functionality but also, through careful modulation of circuit activity, enable exploration of causal relationships between neural signals and brain function.
