Neuroprosthetics are the devices that designed to improve or replace the work of an aspect of the nervous system and that are implanted in the nerve system. The cochlear implant is one of the most popularly used neuroprosthetic, it sidesteps the eardrum, and it stimulates the auditory nerves, improving the hearing ability for individuals who would be having the hearing problem. The first cochlear implant was done in 1957 (Sakas).
The development of brain implanted machines interface technology has become a mile stone in the development of neuroprosthetics. Most of the needed technology progresses that will be fundamental for the clinical transformation of brain and machine interface have been developed. These include the most advanced recording electrodes, actuators that are designed to implement mental plans in real and virtual contexts.
There are about three forms of neuro prosthetics such as motor prosthetics, sensory prosthetics, and cognitive prosthetics. Sensory prosthetics are designed to get information from the environment into the sensory areas such as sight and hearing. Motor prosthetics are designed to help in regulating and stimulate the broken motor functions. On the other hand, cognitive prosthetics are the latest in this field and their development is yet to flood in the health field; however, they are designed for the purpose of improving or replacing cognitive parts of the brain that are malfunctioning.
Categories of Neuroprosthetics Devices
Groups of neuro prosthetics devices are usually classified according to the way they are attached and communicate with the nervous system. For instance, the unidirectional sensory stimulations of the CNS have been applied for years in the regulation of pain at the midbrain, thalamic, peripheral nerves, and spinal cord; cochlear are an example of sensory devices. The unidirectional control for the seizures has been in use for years. The simulation of the cerebellum was previously used, and in recent times, the vagus nerve stimulation was used. The two methods are applied without regarding the interictal and ictal state. Nevertheless, most prosthetics devices would be advanced by extending the degree of control that is provided by the feedback (Horch).
Sensory Neuroprosthetic Devices
In the recent time, the advancement of the neuroprosthetic devices has become feasible through the development in various aspects of the needed technology. The simulation of the somatic sensory axons in the peripheral nerves, spinal cord, and the midbrain has been in use in a non-specific design for the purpose of relieving pain. The decoding of the natural sensation has never been attempted, most specifically for the complicated nerves signals. The stimulation of pain involves the insertion of the signal such as electric razor that is perceived to have buzzing feeling. The inserted signal, if recognized in the somatopic parts of discomfort, may mislead the central nervous system into eradicating the pain sensation. Other forms of sensory neuroprosthetics devices comprise the vagus nerve stimulators that are used on epilepsy. Sensory neuroprosthetic devices do not rely on the perception of the conscious of the stimulus but depend on the subconscious brain stimulation.
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An example of a complex sensory neuroprosthetic device is a cochlear prosthesis through which micro stimulation using platinum contacts leads to the activation of the nucleus of cochlear, producing the vibration that is eventually discriminated by individuals. Direct stimulation of the cochlear’s nucleus through the brainstem is being designed, though the decoding of such inputs may be more complex for the patient since the sensory controls are directly stimulated. There are other complex sensory stimulation devices that are being developed including the retinal visual prosthesis that are meant to activate the optical nerves directly in the retina and activation of the visual cortical. These advanced sensory activation systems require high degrees of stimulation and training programs that enable patients to decode such stimuli (Lepore).
Unidirectional Motor Neuroprosthetics Devices
Though initially they were developed for the pain management, deep brain activators implants were eradicated from the market in the 1980s. Nevertheless, Medtronics designed new fashions of the deep brain activators electrodes, which received FDA endorsement for the application in the movement disorders. Currently, deep brain activators are endorsed for the tremor control, dystonia, and Parkinson’s disease. As a result of the availability of the deep brain activation devices, and unidirectional stimulator systems, additional experiments using these devices for advanced application beyond motor control are being developed. The present generation of deep brain activators appears to have motor control using the constant stimulation of the abnormal motor circuits, in the same way as the way the thalamotomy and pallidotomy functioned.
The Deep Brain System has become a general template for choice among other brain implants due to the direct brain electrodes, the related telemetry and circuitry needed for the external control (Lim).
Other Unidirectional Neuroprosthetic Devices
The availability of the Deep Brain Stimulators systems has caused its consideration for the application in the psychosurgery. The previous application of the brain surgery to manage disorders of thought and mind usually entailed coercion, which is frontal lobotomies that was performed by mental instructors, it also involved permanent lesions, and these techniques had high risks of side effects and even death. Deep Brain Stimulators are usually considered to offer temporary and reversible effects where the patient has control to turn on and off at will. This gives the patient autonomy, which is made possible through medical treatments (Krames). The safety of Deep Brain Stimulation is also a considerable improvement over the brutal versions of frontal lobotomy and psychosurgery that were performed in the earlier days. Therefore, the DBS may be considered as an alternative for psychiatric disorders where medical treatment has not succeeded. The two common surgical sites that are considered to be the cingulum, as opposed to the cingulotomy that is based on the lesion, and the anterior limb that is found in the internal capsule. The only disorder of DBS that is currently under scrutiny is obsessive compulsive disorder and depression.
Both depression and obsessive compulsive disorders severely affect the patients’ functioning. Depression has in some cases led to suicide or its attempt, this lead to over hospitalization of such patients. The DBS is a significant development over the previous version of lesion surgery that is used to treat the above conditions since the stimulation may be designed better and can be operated by the patient if there are unwanted side effects. Other application of the present DBS system includes constant activation for epilepsy, simulation of substantia nigra reticulata, and trial on the anterior thalamic stimulation. These forms of activations tend to affect seizure, though their mechanisms on these roles are yet to be developed. Nevertheless, these stimulations are believed to cause loss of activation efficacy (tachyphylaxis) with constant stimulation because of the plasticity in the circuits activated. These results imply that the demand activation system with the intermittent regulated stimulation may be optimal (Hong).
All neuroprosthetic devices mentioned in the three categories are one-way systems. They just allow a one-way communication with the central nervous system without providing feedback. The current neuroprosthetisis applies indirect channels to communicate to the central nervous system using either micro stimulation or microstimulation of motor output or nerve detection. The examples provided in the above discussion are an illustration of problems related to direct interaction with the central nervous system, and it is required to provide training to the patients to improve the performance of these devices (Pallikarakis).
Bidirectional Neuroprosthetics Devices
A bi-directional system allows the neuroprosthetic device to adjust itself depending on the given demand controls that are needed. For instance, for the seizures, systems are designed in a way that it can sense the pre-ictal and ictal stimuli and cause an anticonvulsant or anti-epileptogenic stimulation rather than a constant activation. In case of the motor, this would consider natural training effects that are critical for motor learning.
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Deciphering Central Nervous System Information
The information received in the CNS is principally purposed for a potential action that is meant to serve as a communication medium. The processing of these potential communications occurs at multi levels that include presynaptic and postsynaptic. In some instances, neurons aggregate leading to the extra cellular rundown of the individual action. These reflections of numerous neurons take place, where they are closely packed (Pallikarakis).
Current Development and Implementation of Motor Neuroprosthetic Device
Intense research that is focused on the understanding of the mechanisms` complication through which neuronal stimulation is translated into motor action has been undertaken. Generally, it is believed that multielectrode constitute one of the promising technological advancement for obtaining information useful for stimulation of motor. The pattern of the raw brain signals from this method seems to highlight the essential attributes of time resolution through decoding of action causing occurrences. The problem that remains is the process of practical implanting into the brain; this is a risky undertaking for any neurosurgeon. There are possibilities of causing neurological injuries and infection. Apparently, a noninvasive method would be better, however, there is no patient for an externally recorded signal who exists. For these reasons, the multi electrode method is preferred. As a matter of fact, single neuron designs of such a patient BMI via implanted neurotrophic electrodes have been carried out. The purposes of applying multi neuron output calling for implanted electrodes array in the brain other than the external signal, communication within the nerve system is passed through a combination of outputs originating from individual neurons. The aim of the immediate multi neuron amplification of the channel and processing of signals which allow updates from the output control system (Krames).
Recording Methods and Locations
Based on the most recent emphasis researching neurons in behavior subjects, numerous electrode versions have emerged and are potentially able to adapt the BMI. The main factors considered during designing of the electrode for the human brain are the qualities of the signal received the duration of the signal after implantation and the size of electrodes. There are different approaches that are used to address these issues. The two key forms of electrode versions applied in a recent study that could be adapted in BMI application are the printed circuit silicon and microwire arrays. The microwire arrays are made of individual wires from the stainless steel, platinum or tungsten with a diameter of approximately 15 micro meters. They are arranged in a configured manner. The wires are insulated, and their tips are made blunt to allow the recording to take place only at the tip of the wire. According to research, blunt wires have been identified as the best with long-term recording, as opposed to sharp ended electrodes that are intended for acute recording of the communication. However, blunt tips have poor penetration to the covering of the brain during implanting. This problem is overcome for sub cortical recording through the opening of the pia and inserting the electrode via a guide tube. The opening of pia surgically may remove blood vessels, which would lead to seizures. There is also a risk of injuring the cortex that would make it difficult to obtain signals from the cortical layer.Therefore, a blunt ended microwire remains a challenge. During implanting, the recording wires are linked to the connector that is attached to the head stage, where filtering, amplification, and processing of the signal begin. Applying the microelectrode arrays, each of the wire is able to record about four units that are within the overall yielding of a unit for each electrode. Through implanting of a large arrays in different regions that are likely to be relevant in generating motor movements, above 100 neurons were recorded simultaneously in the non-human primates. The recordings are still relatively stable within the least decay in the individual neurons that are identified over a several years period (Parasuraman).
Though largely the number of individual cells decays at a slow rate, it is likely that the same neurons may not be recorded each instance. This becomes necessary during analysis and transformation of the data stream to come up with valuable information that can be used within the minimum time on the part of the patient. In case the different neurons are stimulated daily, then the question needs to be asked on whether the BMI have to be retained on the daily basis and whether the information so obtained is stable and indicates that patients retain the information from training. Various designs of silicon electrode and biologically derived electrodes for detecting the signals from multiple or single neuron have been designed, though, their stability at long-run is questionable.
Simple micro wires have been applied successfully for the chronic recording in both human and animals for over a half a century. The micro wires are preferred for they are of low resistance and are able to detect numerous neurons at ago because of their large surface area. The platinum micro wires show minimal damage at the point where the electrode comes into contact with the brain even there where is multiple activation. They are also known for their low toxicity with DBS electrodes. The normal size of these micro wires is approximately 30 to 40 micro meter; they are insulated using Teflon, while the cut end represents the cross section area necessary for reception. Whether the cortical and sub cortical would be preferred for electrode implantation need further research. For years, neuro physiology studies have developed massive bodies of knowledge regarding the motor cortex. The research by Hong (2011) has proved that information concerning motor management of limbs is implanted in the outputs of the cortical neurons. Similarly, information shows that sub cortical locations contain information that is needed for coordination of motor movement of the extremities (Hong).
Implementation of a Neuroprosthetic Communication Device
Apart from the group of patients suffering from motor malfunctions, there is a considerably large group of patients who have communication difficulty. In the cases of cortical damage, this difficulty would be receptive aphasia or receptive, for instance, while cerebral palsy entails a global difficulty in the motor output and obstruction of the voice communication. Presently, such patients rely on the minimum residual motor ability for output, for instance, using an elbow or using toes for typing.
There is an established collection of devices that use binary choices for communication purpose and activity choice, virtual keyboards, and advanced computer applications are already in the market. However, the gadgets such as virtual keyboards could function optimally with advanced signal control from the central nervous system. Therefore, BMI or brain-computers have been long used for patients suffering from communication malfunctions. The first brain implants of one channel electrodes were meant to develop and improve communication in the case of patients who were highly disabled, more so, those who had had locked-in syndromes and severe strokes. The purpose of the implants in such patients was to provide an improved communication output via virtual keyboards with computer controlled cursors, this device attained significant success. Therefore, more complicated multi neuron BMI could offer even better indication throughout that could enable more advanced communication and integration into the community. All the plans and advancements that have been made for multi-neuron implants, response processing, and the connection to the external device is applicable equally in communication disorder as well as the motor malfunction (Schouenborg).
Future Scope and Conclusion
The development of neuroprosthetic devices undergoes a clearly cut proposition that multi neuron outputs can provide improved signals for the external aids control in case the decoding of the signals from the specific brain areas can be accomplished. Therefore, a neuroprosthetics device to some large extent provides a sight into translational neurosurgery and neuroscience, specifically designed devices. Most laboratories have persuasively demonstrated that the purpose of an efficient motor neuroprosthesis is possible in non-human primates, and further, a group of researchers have taken this to the human being application with significant success (Krames). Morally, providing an enhanced functional communication or motor independence to patients who were disabled in such areas should be the ultimate goal and not the relieving of tremor. For instance, the brain implants can be done to cure tremor, with significant success. Considerably large number of neuroprosthetic aids is already available in the common clinical application and numerous motor, and sensory devices have been developed or are at advance levels of their development. The technological advancement for the improved sophistication of the implanted aids is continuously advancing, anticipating that in the near future there will be the likelihood for both efficient motor control and advanced sensory enhancement.
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