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Neuroprosthetics is an area of neuroscience concerned with neural prostheses, that is, artificial devices used to replace damaged or missing parts of the brain. The neuroprosthetic seeing the most widespread use is the cochlear implant, which is in approximately 85,000 people worldwide as of 2005.

History

Research was undertaken by the American CIA in the 1950s as one aspect of the MKULTRA designator - notably Subprojects 86 [originally an invasive prosthetic identifier thought to expand in reporting body responses such as blood pressure or tremor], 94 [neurostimulus in animals immediately defining direction of movement and control], and 119 [remote "reassembly" or unification of monitored neural impulse into a useable data product]. CIA documentation - mostly the original queries with budget numbers for the initial years of research though none of the contractor's reporting - was released in response to congressional inquiry in the 1970s; in retrospect the pattern of release suggesting legacy factions in the CIA effectively used the opportunity to undermine then-director Stansfield Turner.

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. 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].

Current research

Visual prosthesis

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 micrometres) 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.

Other prostheses

In 2003 Patrick Kennedy (Emory and Georgia Tech) had an operable if somewhat primitive system designed, allowing a handicapped person to spell words with nerve impulses.

Much of the ongoing research in neuroprosthetics concerns retinal implants and cochlear implants, though for example at the University of Southern California research is done for hippocampal implants.

Commercial technology

Medtronic is a significant commercial name in the emergent market.

References

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.

See also

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