Neuroprosthetics

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Neuroprosthetics (also called Neural Prosthetics) is a discipline related to neuroscience and biomedical engineering concerned with developing neural prostheses, artificial devices to replace or improve the function of an impaired nervous system. The neuroprosthetic seeing the most widespread use is the cochlear implant, with approximately 100,000 in use worldwide as of 2006.^[1]

Contents 1 History 2 Sensory prosthetics 2.1 Visual prosthetics 2.2 Auditory prosthetics 2.3 Prosthetics for pain relief 3 Motor prosthetics 3.1 Bladder control implants 3.2 Motor prosthetics for conscious control of movement 4 Sensory/Motor prosthetics 5 Cognitive prosthetics 6 Commercial technology 7 References 8 Further reading 9 See also 10 External links

[edit] History

The first cochlear implant dates back to 1957. Other landmarks include the first motor prosthesis for foot drop in hemiplegia in 1961, the first auditory brainstem implant in 1977 and a peripheral nerve bridge implanted into spinal cord of adult rat in 1981.^[2] Paraplegics were helped in standing with a lumbar anterior root implant (1988) and in walking with Functional Electrical Stimulation (FES).

Regarding the development of electrodes implanted in the brain, an early difficulty was reliably locating the electrodes, 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 Parkinson's Disease. The problem with either approach is that the brain floats free in the skull while the probe does not, and relatively minor impacts, such as a low speed car accident, are potentially damaging. Some researchers, such as Kensall Wise at the University of Michigan, have proposed tethering 'electrodes to be mounted on the exterior surface of the brain' to the inner surface of the skull. However, even if successful, tethering would not resolve the problem in devices meant to be inserted deep into the brain, such as in the case of deep brain stimulation (DBS).

Research has also been undertaken by the American CIA in the 1950s as part of the MKULTRA program, although it is not certain all the subprojects fully met the definition of a 'neuroprosthetic.' Subproject 86 (developing an invasive prosthetic identifier thought to expand in reporting body responses such as blood pressure or tremor) might not have, but subproject 94 (neurostimulus in animals immediately defining direction of movement and control) and subproject 119 certainly did. The latter included 'monitoring' which is the remote "reassembly" or unification of monitored neural impulse into a usable data product, and 'stimulating' which is inducing say visual stimulus directly to the visual cortex, bypassing the optic nerve/tract which is still not entirely understood. Audio and even tactile sensation can be similarly induced, but the larger history of subproject 119 and the relationship between the CIA and the National Institute of Health (NIH) which contracted out some of the work has not been made public. William Heetderks is thought to have served as the interagency focal but again that is emergent.

[edit] Sensory prosthetics

[edit] Visual prosthetics

Main article: Visual prosthetic

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. By the 1940s, researchers had established the concept of artificial electrical stimulation of the visual cortex, and 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 Brindley's 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.

With this new technology, several scientists, including Karin Moxon at Drexel, John Chapin at SUNY, and Miguel Nicolelis at Duke University, started research on the design of a sophisticated visual prosthesis. Other scientists have disagreed with the focus of their research, arguing that the basic research and design of the densely populated microscopic wire was not sophisticated enough to proceed.

[edit] Auditory prosthetics

Main articles: cochlear implant and auditory brainstem implant

A cochlear implant (or "bionic ear") is a surgically implanted device that can help provide a sense of sound to a person who is profoundly deaf or severely hard of hearing. Unlike hearing aids, the cochlear implant does not amplify sound, but works by directly stimulating any functioning auditory nerves inside the cochlea with electrical impulses. External components of the cochlear implant include a microphone, speech processor and transmitter. Similar to the cochlear implant, an auditory brainstem implant is a surgically implanted device, that through presenting electrical stimulation to the brainstem of the recipient, provides a sense of sound to the recipient. The external components of the auditory brainstem implant are the same as for a cochlear implant.

[edit] Prosthetics for pain relief

Main article: Spinal Cord Stimulator

The Spinal Cord Stimulator or (Dorsal Column Stimulator) is used to treat chronic neurological pain. It is implanted near the dorsal surface of the spinal cord and an electric impulse generated by the device provides a "tingling" sensation that alters the perception of pain by the patient. A pulse generator or RF receiver is implanted in the abdomen or buttocks. A wire harness connects the lead to the pulse generator.

[edit] Motor prosthetics

Devices which support the function of autonomous nervous system include the implant for bladder control. In the somatic nervous system attempts to aid conscious control of movement include Functional electrical stimulation and the lumbar anterior root stimulator.

[edit] Bladder control implants

Main article: Sacral anterior root stimulator

Where a spinal cord lesion leads to paraplegia, patients have difficulty emptying their bladders and this can cause infection. From 1969 onwards Brindley developed the sacral anterior root stimulator, with successful human trials from the early 1980s onwards.^[3] This device is implanted over the sacral anterior root ganglia of the spinal cord; controlled by an external transmitter, it delivers intermittent stimulation which improves bladder emptying. It also assists in defecation and enables male patients to have a sustained full erection.

The related procedure of sacral nerve stimulation is for the control of incontinence in able-bodied patients.^[4]

[edit] Motor prosthetics for conscious control of movement

Main article: Brain-computer interface

Researchers are attempting to build motor neuroprosthetics that will help restore movement and the ability to communicate with the outside world to persons with motor disabilities such as tetraplagia or amyotrophic lateral sclerosis.

To capture electrical signals from the brain, scientists have developed microelectrode arrays smaller than a square centimeter that can be implanted in the skull to record electrical activity, transducing recorded information through a thin cable. After decades of research in monkeys, neuroscientists have been able to decode neuronal signals into movements. Completing the translation, researchers have built interfaces that allow patients to move computer cursors, and they are beginning to build robotic limbs and exoskeletons that patients can control by thinking about movement.

The technology behind motor neuroprostheses is still in its infancy. Investigators and study participants continue to experiment with different ways of using the prostheses. Having a patient think about clenching a fist, for example, produces a different result than having him or her think about tapping a finger. The filters used in the prostheses are also being fine-tuned, and in the future, doctors hope to create an implant capable of transmitting signals from inside the skull wirelessly, as opposed to through a cable.

Preliminary clinical trials suggest that the devices are safe and that they have the potential to be effective.^{[citation needed]} Some patients have worn the devices for over two years with few, if any, ill effects.^{[citation needed]}

Prior to these advancements, Philip Kennedy (Emory and Georgia Tech) had an operable if somewhat primitive system which allowed an individual with paralysis to spell words by modulating their brain activity. Kennedy's device used two neurotrophic electrodes: the first was implanted in an intact motor cortical region (e.g. finger representation area) and was used to move a cursor among a group of letters. The second was implanted in a different motor region and was used to indicate the selection.^[5]

Developments continue in replacing lost arms with cybernetic replacements by using nerves normally connected to the pectoralis muscles. These arms allow a slightly limited range of motion, and reportedly are slated to feature sensors for detecting pressure and temperature.^[6]

Dr. Todd Kuiken at Northwestern University and Rehabilitation Institute of Chicago has developed a method called targeted reinnervation for an amputee to control motorized prosthetic devices and to regain sensory feedback.

[edit] Sensory/Motor prosthetics

In 2002 an implant was interfaced directly into the median nerve fibres of the scientist Kevin Warwick. The electrode array inserted contained 100 electrodes, of which 25 could be accessed at any one time. The signals produced were detailed enough that a robot arm developed by Warwick's colleague, Peter Kyberd, was able to mimic the actions of Warwick's own arm and provide a form of touch feedback via the implant.^[7]

[edit] Cognitive prosthetics

Sensory and motor prostheses deliver input to and output from the nervous system respectively. Theodore Berger at the University of Southern California defines a third class of prostheses^[8] aimed at restoring cognitive function by replacing circuits within the brain damaged by stroke, trauma or disease. Work has begun on a proof-of-concept device - a hippocampal prosthesis which can mimic the function of a region of the hippocampus - a part of the brain responsible for the formation of memories.^[9][10]

[edit] Commercial technology

Medtronic and Advanced Bionics are significant commercial names in the emergent market of Deep Brain Stimulation. Cyberkinetics is the first venture capital funded neural prosthetic company.

[edit] References

[edit] Further reading

Santucci DM, Kralik JD, Lebedev MA, Nicolelis MA (2005) "Frontal and parietal cortical ensembles predict single-trial muscle activity during reaching movements in primates." Eur J Neurosci. 22(6): 1529-1540.

Lebedev MA, Carmena JM, O'Doherty JE, Zacksenhouse M, Henriquez CS, Principe JC, Nicolelis MA (2005) "Cortical ensemble adaptation to represent velocity of an artificial actuator controlled by a brain-machine interface." J Neurosci. 25: 4681-4893.

Nicolelis MA (2003) "Brain-machine interfaces to restore motor function and probe neural circuits." Nat Rev Neurosci. 4: 417-422.

Wessberg J, Stambaugh CR, Kralik JD, Beck PD, Laubach M, Chapin JK, Kim J, Biggs SJ, Srinivasan MA, Nicolelis MA. (2000) "Real-time prediction of hand trajectory by ensembles of cortical neurons in primates." Nature 16: 361-365.

[edit] See also

• Technologies: Brain-computer interface, Brain implant, Cyberware, Neurotechnology, Prosthetics, Cyborg
• Disciplines: Cognitive Science, Neural engineering, Neuroscience
• People: Miguel Nicolelis, Peter Kyberd, Kevin Warwick

[edit] External links

(for a list of universities see Neural Engineering - Neural Engineering Labs)

• The open-source Electroencephalography project and Programmable chip version, Sourceforge open source EEG projects
• Dr. Theodore W. Berger's website
• CIMIT - Center For Integration Of Medicine And Innovative Technology - Advances & Research in Neuroprosthetics