Abstract
Neural interfaces, which enable the recording and stimulation of living neurons, have emerged as valuable tools in understanding the brain in health and disease, as well as serving as neural prostheses. While neural interfaces are typically based on electrical transduction, alternative energy modalities have been explored to create safe and effective approaches. Among these approaches, optical methods of linking neurons to the outside world have gained attention because light offers high spatial selectivity and decreased invasiveness. Here, we review the current state-of-art of optical neural interfaces and their clinical applications. Optical neural interfaces can be categorized into optical control and optical readout, each of which can be divided into intrinsic and extrinsic approaches. We discuss the advantages and disadvantages of each of these methods and offer a comparison of relative performance. Future directions, including their clinical opportunities, are discussed with regard to the optical properties of biological tissue.
Highlights
Micromachines 2021, 12, 925. https://There are billions of neurons in the human body which are connected to organs for regulating their functions
There are numerous neural prosthesis devices already developed to help patients suffering from diseases that have been known to be incurable by modern pharmacological or surgical treatment
Unraveling the function and connectivity of neural circuits is essential for determining the specific target inside the brain area and assessing brain stimulation which involves deliberately modulating specific neurons accompanied by recording the responses
Summary
There are billions of neurons in the human body which are connected to organs for regulating their functions. Despite the robustness of the electrical neural interface, it requires invasive surgery when placing the electrode near the target neural region. Since 1971 when Fork showed direct activation of abdominal ganglion neurons in Aplysia californica by shining a 488-nm laser, researchers have investigated the direct control of neural cells via optical illumination [16] We classified this type of optical neural stimulation as an intrinsic neural stimulation as it requires no neural engineering prior to light irradiation [8]. In early 2000, researchers engineered the neuron by inserting exogenous materials (i.e., genes that eventually expressed to acquire light-sensitivity, nanomaterials, chemical compounds) to endow the light sensitivity of the neuron itself [11] We entitled this type of neuromodulation as an extrinsic neural stimulation. The perspective of optical neural interfaces, especially in the view of clinical applications, are discussed
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