Positive Technology Journal

Neuroprosthetics is a relatively new discipline at the boundaries of neuroscience and biomedical engineering, which aims at developing implantable devices to restore neural function. The most popular and clinically successfull neuroprosthesis to date is the cochlear implant, a device that can restore hearing by stimulating directly the human auditory nerve, by bypassing damaged hair cells in the cochlea.

Visual prostheses, on the other hand, are still in a preliminary phase of development, although substantial progress has been made in the last few years. This kind of implantable devices are designed to micro-electrically stimulate nerves in the visual system, based on an image from an external camera. These impulses are then propagated to the visual cortex, which is able to process the information and generate a “pixelated” image. The resulting impression has not the same quality as natural vision but it is still useful for performing basic perceptual and motor tasks, such as identifying an object or navigating a room. An example of this approach is the Boston Retinal Implant Project, a large joint collaborative effort that includes, among others, the Harvard Medical School and MIT.

Another area of neuroprosthetics is concerned with the development of implantable devices to help patients with diseases such as spinal cord injury, limb loss, stroke and neuromuscolar disorders improving their ability to interact with their environment and communicate. These motor neuroprosthetics are also known as “brain computer interfaces” (BCI), which in essence are devices that decode brain signals representing motor intentions and convert these information into overt device control. This process allows the patient to perform different motor tasks, from writing a text on a virtual keyboard to driving a wheel chair or controlling a prosthetic limb. An impressive evolution of motor neuroprosthetic is the combination of BCI and robotics. For example, Leigh R. Hochberg and coll. (Nature 485, 372–375; 2012) have reported that using a robotic arm connected to a neural interface called “BrainGate” two people with long-standing paralysis could control the reaching and grasping actions, such as drinking from a bottle.

Cognitive neuroprosthetics is a further research direction of neuroprosthetics. A cognitive prosthesis is an implantable device which aims at restoring cognitive function to brain-injured individuals by performing the function of the damaged tissue. One of the world’s most advanced effort in this area is being lead by Theodore Berger, a biomedical engineer and neuroscientist at the University of Southern California in Los Angeles. Berger and his coll. are attempting to develop a microchip-based neural prosthesis for the hippocampus, a region of the brain responsible for long-term memory (IEEE Trans Neural Syst Rehabil Eng 20/2, 198–211; 2012). More specifically, the team is developing a biomimetic model of the hippocampal dynamics, which should serve as a neural prosthesis by allowing a bi-directional communication with other neural tissue that normally provides the inputs and outputs to/from a damaged hippocampal area.