neuroprosthetics

Abstract
Neuroprosthetics is an area of Neuroscience concerned with neural prostheses, that is artificial devices used to replace or improve the function of an impaired nervous system. There have been several important advances in recent years in neural prosthetic technology, but a critical area for long-term functional implants will be the engineering of stable neuron/electronic interfaces for the bidirectional flow of information between the electronic and the biological systems. Neural implants may be placed directly in the brain or along the peripheral nervous system. In both cases, engineers, material scientists, and physicists must discover the best way to create safe and effective electrical interfaces without causing physical damage to the cell and surrounding tissues. The signal coupling between the electrodes and neurons depends on the implant materials, geometry, architecture, and the stimulating signal characteristics such as voltage/current, amplitude, duration, polarity, etc. Substrate, encapsulation, and active materials must meet strict electrochemical requirements such as long-term stability, biocompatibility, and resistance to corrosion in a physiological environment. Additionally, the implant should match the mechanical modulus of the surrounding tissue to prevent injury due to micromotion and allow for adequate exchange of

nutrients and waste so that the surrounding tissue remains healthy.
Introduction :
Until recently, the concept of helping the deaf to hear, the blind to see, and the paralyzed to walk was more the province of science fiction or theology than of clinical medicine. Today, however, individuals with profound deafness who have been fitted with cochlear prostheses are able to hear, and to enjoy relatively normal conversations with family, friends and fellow workers. This approach to hearing restoration is rapidly becoming a widely accepted therapy. The neuroprosthetic seeing the most widespread use is the cochlear implant, which is in approximately 100,000 people worldwide as of 2006. An early difficulty in the development of neuroprosthetics was reliably locating the electrodes in the brain, originally done by inserting the electrodes with needles and breaking off the needles at the desired depth. Recent systems utilize more advanced probes, such as those used in deep brain stimulation to alleviate the symptoms of Parkinsons Disease. Researchers in the US have also implanted electrodes into the motor regions of the brain in paralyzed patients, and have been able to use recorded neural activity to infer the desires of these patients, enabling them to control the cursor on a computer screen simply through volitional thought. These attempts to restore lost sensory and motor function are the result of new neuroprosthesis-based therapy, a field that is still in its infancy. The most famous and widely-used neuroprosthetic is the cochlear implant, which bypasses the eardrum and directly stimulates the human auditory nerve, giving the power of hearing to those who lack it. The first cochlear implant was built in 1957, and today, these implants are used by over 100,000 people.
There are three main types of neuroprosthetics - sensory prosthetics, motor prosthetics, and cognitive prosthetics. Sensory prosthetics get information into sensory areas like hearing and sight, motor prosthetics help regulate or stimulate malfunctioning motor functions, and cognitive prosthetics are a largely still-on-the-drawing board field of future prosthetics for replacing or improving problem areas in the brain itself. Although the term "neuro" makes us think of the brain, all neuroprosthetics in use today replace nervous system aspects external to the brain.
Research in visual neuroprosthetics has given rise to extremely fine electrodes, thinner than a human hair. This has helped progress tangential areas of neurophysiology, but unfortunately true visual prostheses - devices which would allow the blind to see - are still in development.

Description:
The neural code is the software, set of rules, syntax, that transforms electrical pulses in the brain into perceptions, memories, decisions. A solution to the neural code could – in principle – give us almost unlimited power over our psyches, because we could monitor and manipulate brain cells with exquisite precision by speaking to them in their own private language.
Most disorders of the nervous system result from localized sensory or motor pathologies attributable to disease or trauma. The emerging field of neuroprosthetics is focused on the development of therapeutic interventions that will be able to restore some of this lost neural function by selective electrical stimulation of sensory or motor pathways, or by harnessing activity recorded from remnant neural pathways. A key element in this restoration of function has been the development of a new generation of penetrating microelectrode arrays that provide unprecedented selective access to the neurons of the CNS and PNS. The active tips of these microelectrode arrays penetrate the nervous tissues and abut against small populations of neurons or nerve fibers, thereby providing selective access to these cells. These electrode arrays are not only beginning to provide researchers with the ability to better study the spatiotemporal information processing performed by the nervous system, they can also form the basis for new therapies for disorders of the nervous system. In this Review, three examples of this new generation of microelectrode arrays are described, as are potential therapeutic applications in blindness and spinal cord injury, and for the control of prosthetic limbs.
The neuroprosthetic approach to restoring these lost functions is based on arrays of microelectrodes implanted into neural tissues, which can 'talk' and 'listen' to large numbers of small groups of neurons in the CNS and PNS. These implanted electrode arrays enable direct communication with still-functioning parts of the sensory and motor neural pathways. By stimulating and recording from these neurons, it is possible to bypass, to a limited degree, regions of the nervous system that have been damaged by inherited or acquired disease, or by traumatic injury. This approach is, however, made difficult by the complexity of the CNS and PNS.
several possible applications of this technology in sensory and motor disorders, and concludes with a brief description of some of the remaining hurdles that must be overcome before neural interface devices can become clinical tools.
1. Electrophysiology, focusing on device design, electrophysiological measurements and signal analysis,
Or
2. Tissue Assessment, focusing on immune-histochemistry, imaging and quantitative tissue analysis.

The success of the cochlear neuroprosthesis, however, highlights two important features of our nervous system: first, the brain has a remarkable capacity to make use of even the most limited amount of sensory stimulation, and second, the plasticity of these neural circuits is such that the brain can interpret somewhat inappropriate but systematic stimulation of sensory pathways, and can use this information to make useful judgments about the world.
Research into neuroprosthetics is an ongoing and cutting-edge area of science. We should expect to see many more developments in the future, some of which will challenge common assumptions about the interface between the mind and machines.
Focus on the latest advances to control/engineer neuron-electronic interfaces to produce stable, no damaging implants with greater longevity than what is possible today. Session topics will spotlight the latest efforts to achieve the most effective and safest strategies to communicate with neurons.
Devices are designed to reproduce or substitute for neurological and physiological function that has been lost to injury or disease. Wearable electrical stimulation systems deliver impulses to peripheral nerves. They induce a variety of beneficial effects, including muscle building, relaxation of spastic muscle, improvement of blood circulation, reduction of joint contractures and alleviation of pain. Neuro-Prosthetics improve function in a way that is “physiological”. Patients with central nervous system dysfunction lose function when muscles become paralyzed.

Physiological walking for foot drop in CNS disorders

However, muscles can be stimulated with enough force to induce purposeful movement. Bioflx integrates electrical stimulation into customized and wearable garments. These garments ensure that the muscle is properly stimulated. They accurately and precisely place the electrode over.

Wearable Therapy Vest for the Management of Chronic Pain

Areas of application:
Neuroprosthetic can be applicable in
1. Loss of hand or legs, Example CNS disorders.
2. Suffering from Pain, example due to Curvature in spine (scoliosis).
3. When muscles become paralyzed.
4. To regain the power of eye sight and hearing capability.

One of the prominent goals in neuroprosthetics is a visual supplement, noting roughly 95% of all people considered 'blind' suffer significant impairment but have some capability (for example, seeing some sort of blur) - only about 5% of 'blind' people are totally blind.
In the late 1960s, British scientist Giles Brindley produced breakthrough findings with a system for placing electrodes on the brain's surface. When specific areas of the brain were stimulated in blind volunteers, all reported "seeing" phosphenes that corresponded to where they would have appeared in space. However, experiments were discontinued because of the uncomfortably high currents required for stimulation on the surface of the brain.
Encouraged by this work, the National Institutes of Health undertook a project to develop and deploy an interface based on ultrafine wire (25 to 50 micrometers) densely populated with electrode sites that could be implanted deep into the visual cortex, thus requiring less current than original design. This work led to new electrode technology—finer than the width of human hair—that could be safely implanted in animals to electrically stimulate, and passively record, electrical activity in the brain. The efforts produced significant advances in neurophysiology, with publication of hundreds of papers in which researchers attempted to develop an electronic interface to the brain.

Nicolelis Experiment:

Prof Miguel Nicolelis a Neuroscientist of Duke university conducted experiment on a monkey for studying the nature of brain’s instruction format. Nicolelis arranged a electro array in the monkey’s brain and connected it to computer. Nicolelis and his team trained the monkey to play a simple game which needs to operate a joy stick so that the cursor on the screen will be placed on a randomly appearing circle on screen. They recorded the intensity of signals which are coming from the monkey’s brain when it is trying to move its hand on the joy stick. They offered juice to the monkey whenever it completes the task within five seconds. Nicolelis and team designed a robotic hand which works according to the signals received from monkey’s brain through computer. After the monkey gained enough control on the joystick they disconnected the power supply to the joystick. Unknowing this monkey continued to squeeze the joystick. They observed the readings of its brain which are identical to the previous readings.

When these signals are given to the robotic hand attached to the computer it worked properly and the movements of this device is identical to that of monkey’s operation. Thus, it can also be applicable for all living beings. Hence it is proved that electronic devices can be controlled directly from brain (by the thought itself).

Conclusion:
The capability of the individuals can be improved through Neuroprosthetics. The quality of work can be considerably increased. We must create awareness among the people who are suffering from disabilities, so that we can increase their living standards.

References :
http://ecow.engr.wisc.edu/cgi-bin/get/bme/515/webster/neuralassistdevice...
http://en.wikipedia.org/wiki/Neuroprosthetics
http://www.youtube.com/watch?v=fHP7MFilWKg
http://www.youtube.com/watch?v=7-cpcoIJbOU&feature=related