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[1] in use worldwide as of 2006.
History
editThe first cochlear implant dates back to 1957. Implanted heart pacemakers were first trialled in 1958 and successfully in 1960, whilst externally pacemakers significantly predate this. Other landmarks (according to [2]) 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. Paraplegics were helped in standing with a lumbar anterior root implant (1988) and in walking with Functional Electrical Stimulation (FES) (from 1986).
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 (ref?). 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].
Research has also been undertaken by the American CIA in the 1950s as part of the MKULTRA program, although it is uncertain whether this meets the definition of neuroprosthesis. Examples: Subproject 86 (developing an invasive prosthetic identifier thought to expand in reporting body responses such as blood pressure or tremor), subproject 94 (neurostimulus in animals immediately defining direction of movement and control) and subproject 119 (remote "reassembly" or unification of monitored neural impulse into a useable data product).
Sensory prosthetics
editVisual prosthetics
editOne 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.
Auditory prosthetics
editA 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.
Prosthetics for pain relief
editThe 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.
Motor prosthetics
editDevices which support the function of autonomous nervous system include the Artificial Pacemaker and an 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.
Heart pacemaker
editA medical device designed to regulate the beating of the heart. The purpose of an artificial pacemaker is to stimulate the heart when either the heart's native pacemaker is not fast enough or if there are blocks in the heart's electrical conduction system preventing the propagation of electrical impulses from the native pacemaker to the lower chambers of the heart.
Bladder control implants
editWhere a spinal cord lesion leads to paraplegia, patients have difficulty emptying their bladders and this can cause infection. From 1969 onwards Brindley [3] developed the sacral anterior root stimulator, with successful human trials from the early 1980's onwards. 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 [4] is for the control of incontinence in otherwise able-bodied patients.
motor prosthesis for foot drop in hemiplegia,
peripheral nerve bridge implanted into spinal cord of adult rat in 1981.
Paraplegics were helped in standing with a lumbar anterior root implant (1988)
in walking with Functional Electrical Stimulation (FES).
In 1995 human trials began for foot drop splint,
and for bionic glove and
freehand system for quadriplegics,
sacral anterior root stimulator
microelectrode arrays,
IST (Implanted Stimulator Telemeters),
IJAT (Implanted Joint Angle Transducers),
intradural electrodes for walking in paraplegics etc.
Motor prosthetics for conscious control of movement
editIn 2003 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 uses two neurotrophic electrodes: the first is implanted in an intact motor cortical region (e.g. finger representation area) and used to move a cursor among a group of letters. The second is implanted in a different motor region and used to indicate the selection. [5]
More recently, there have been successful experiments completely 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]
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Cognitive prosthetics
editSensory 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 [7] 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.
Commercial technology
editMedtronic 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, and has the first human trial.
freehand system for quadriplegics ???
References
edit- ^ Laura Bailey. "HUniversity of Michigan News Service". Retrieved February 6, 2006.
{{cite web}}: Cite has empty unknown parameter:|1=(help) - ^ Handa G (2006) "Neural Prosthesis – Past, Present and Future" Indian Journal of Physical Medicine & Rehabilitation 17(1)
- ^ Brindley GS, Polkey CE, Rushton DN (1982): Sacral anterior root stimulator for bladder control in paraplegia. Paraplegia 20: 365-381.
- ^ Schmidt RA, Jonas A, Oleson KA, Janknegt RA, Hassouna MM, Siegel SW, van Kerrebroeck PE. Sacral nerve stimulation for treatment of refractory urinary urge incontinence. Sacral nerve study group. J Urol 1999 Aug;16(2):352-357.
- ^ Gary Goettling. "Harnessing the Power of Thought". Retrieved April 22, 2006.
{{cite web}}: Cite has empty unknown parameter:|1=(help) - ^ David Brown. "Washington Post". Retrieved September 14, 2006.
{{cite web}}: Cite has empty unknown parameter:|1=(help) - ^ Berger T et al (2005) "Restoring Lost Cognitive Function" IEEE Engineering in Medicine and Biology Magazine September/October pg 30-46
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
edit- Technologies: Brain-computer interface, Brain implant, Cyberware, Neurotechnology
- Disciplines: Cognitive Science, Neural engineering, Neuroscience
- People: Miguel Nicolelis
External links
editOrganisations
edit(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
- Brain controlled video game Boy controls video game through brain-machine interface
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Page on Hippocampal Implants
Such a new generation
of neural prostheses would have a profound impact on the
quality of life throughout society; it would offer a biomedical
remedy for the cognitive and memory loss accompanying
Alzheimer’s disease, the speech and language deficits
resulting from stroke, and the impaired ability to execute
skilled movements following trauma to brain regions
responsible for motor control.
The significance of this organizational feature is that, after removing the hippocampus from the brain, transverse slices (400 μm thick) of the structure may be maintained in vitro that preserve a substantial portion of the intrinsic circuitry.
Attempting to accomplish this modeling goal with compartmental neuron models [24], [25] based on cable theory is simply not feasible. The number of parameters required to represent complex dendritic structures and the number and variety of ligand- and voltage-dependent conductances common to hippocampal neurons is simply too large to include in a multineuron network model that is sufficiently compact for a microchip or even a multichip module.
Poisson inputs ...
The modeling effort, identified as the Volterra-Poisson modeling approach, then becomes focused on estimating linear and nonlinear components of the mapping of the known input to the experimentally measured output.
Field potentials are
used as the measure of output
from each of the three
hippocampal regions: population
spikes of dentate granule
cells, population spikes
of CA3 pyramidal cells, and
population EPSPs (excitatory
postsynaptic potentials) of
CA1 pyramidal cells.