Cortical implant

A cortical implant is a subset of neuroprosthetics that is in direct connection with the cerebral cortex of the brain. By directly interfacing with different regions of the cortex, the cortical implant can provide stimulation to an immediate area and provide different benefits, depending on its design and placement. A typical cortical implant is an implantable microelectrode array, which is a small device through which a neural signal can be received or transmitted. The goal of a cortical implant and neuroprosthetic in general is "to replace neural circuitry in the brain that no longer functions appropriately." Cortical implants have a wide variety of potential uses, ranging from restoring vision to blind patients or helping patients with dementia. With the complexity of the brain, the possibilities for these brain implants to expand their usefulness are nearly endless. Some early work in cortical implants involved stimulation of the visual cortex, using implants made from silicone rubber. Since then, implants have developed into more complex devices using new polymers, such as polyimide. There are two ways that cortical implants can interface with the brain, either intracortically (direct) or epicortically (indirect). Intracortical implants have electrodes that penetrate into the brain, while epicortical implants have electrodes that stimulate along the surface. Epicortical implants mainly record field potentials around them and are generally more flexible compared to their intracortical counterparts. Since the intracortical implants go deeper into the brain, they require a stiffer electrode. However, due to micromotion in the brain, some flexibility is necessary in order to prevent injury to the brain tissue. Certain types of cortical implants can partially restore vision by directly stimulating the visual cortex. Early work to restore vision through cortical stimulation began in 1970 with the work of Brindley and Dobelle. With their initial experimentation, some patients were able to recognize small images at fairly close distances.