Brain Stimulation 8 (2015) 439e441
Contents lists available at ScienceDirect
Brain Stimulation journal homepage: www.brainstimjrnl.com
Editorial
Two Laskers and Counting: Learning From the Past Enables Future Innovations With Central Neural Prostheses
Andreas is a young boy who was born deaf. Since he has no auditory nerves, he could not benefit from a cochlear implant (CI). A CI is surgically placed in the cochlea and sends electrical currents to surrounding auditory nerve fibers to elicit hearing sensations. When Andreas was three years old, he received an auditory brainstem implant (ABI) [1]. The ABI is similar to a CI but consists of an electrode array that is placed on the surface of the auditory portion of the brainstem. Today, Andreas is 10 years old and can understand speech well enough to attend school with his normal hearing peers. He is even starting to learn to play the guitar. This remarkable case is one of many that show how electrical stimulation of the brain can restore function. Like many innovations, however, the ABI was met with skepticism and low expectations during its development. There were doubts that the complicated circuitry of the brainstem could be artificially stimulated to restore useful hearing and whether the ABI would be successful in children. Since 1979, visionaries such as William House, William Hitselberger, Douglas McCreery and Vittorio Colletti, pushed forward through these hurdles [2e4]. It is now clear that we underestimated the ability of the brain to adapt to a highly non-normal pattern of neural activation from an ABI [5,6]. More than 1200 deaf people, including children as young as one year, have been implanted with the ABI. Many are able to understand speech and talk on the telephone. History seems to find a way of repeating itself. Before the ABI, a similar type of premature skepticism plagued the CI through its development from the 1960s [7]. Numerous clinicians and scientists, including those who studied the microstructure and physiology of the auditory system, could not believe that any useful hearing would result from the crude activation of peripheral neurons by a small number of electrodes. Regardless, pioneers in the field continued to innovate and develop their ideas that eventually led to the CI, one of the most successful neural prostheses to date. More than 300,000 individuals, including infants younger than a year, have been safely implanted with a CI. Many of these individuals can converse almost normally and have been able to integrate into mainstream society. This is a level of performance that was unthinkable 30 years ago. To recognize this phenomenal achievement, three pioneers who were critical to the success of the CI e Graeme Clark, Ingeborg Hochmair, and Blake Wilson e were awarded the prestigious LaskerwDeBakey Clinical Medical Research Award in 2013 [7]. Support from companies and the government, in addition to the work of several other visionaries such as André Djourno, William House and Blair Simmons, helped catalyze and translate the CI from a disputed concept to a daily reality [8,9]. http://dx.doi.org/10.1016/j.brs.2014.10.016 1935-861X/Ó 2015 Elsevier Inc. All rights reserved.
The success of auditory prostheses contains an important lesson for restoration of function through neural prostheses. The brain has an immense capability to process crude forms of information to make meaningful percepts and actions. This doesn’t mean that any type of input or cues will be effective. For CIs, it took several iterations of stimulation strategies to find patterns that reduced channel interaction and appropriately activated neurons to enable speech perception. The point is that the complexity of the brain shouldn’t be the argument against a neural prosthesis, whether a peripheral or central device. With more advanced technologies that allow for a higher number of closely spaced electrodes in three-dimensional configurations and smart algorithms (e.g., allowing patients to optimize their device based on perceptual and/or neural feedback), there will be greater opportunities to find the “right code” for implementation. So what is next for the auditory implant field? The CI and ABI have both achieved performance levels beyond expectations; however, not all implant users sufficiently benefit from these devices. Most CI and nearly all ABI patients also have poor hearing capabilities in noisy environments and for more complicated inputs such as music or multiple people conversing simultaneously. One major limitation in achieving higher performance appears to be the limited number of independent information channels possible with these implants [10]. The CI sends current through a bony modiolar wall of the cochlea with scattered flow of electrical charge to a variable distribution and reduced number of auditory neurons associated with deafness. The ABI is placed on the surface of the brainstem, resulting in high stimulation levels and large current spread to activate auditory neurons within deeper regions. There are several new directions in the auditory field that have sought to increase the specificity of activation with central neural prostheses, using penetrating electrode arrays within the brainstem, midbrain, thalamus or cortex (e.g., [11,13,24,25]). Two types of these neural prostheses have been investigated in clinical trials. A penetrating ABI (PABI) with tip electrodes on 8 or 10 shanks has been developed and implanted into the auditory brainstem of 10 patients [11]. Encouragingly, the PABI could be safely implanted and stimulated in humans and has achieved greater specificity and lower thresholds of activation than the ABI. The performance, however, has not yet exceeded that of the ABI and CI. Inaccurate placement of electrode sites into the target region was a possible limitation in that study. Another neural prosthesis being explored is the auditory midbrain implant (AMI), which consists of one or two shanks with up to 22 electrode sites that are inserted into
440
Editorial / Brain Stimulation 8 (2015) 439e441
Figure 1. A. Simplified schematic of the brain showing the location of electrode arrays currently implanted in humans for restoring hearing or suppressing tinnitus. The CI, ABI, PABI, and AMI are example arrays developed by Cochlear Limited (N.S.W., Australia) and the cortical implant is an example array developed by St. Jude Medical (TX, USA). Similar types of devices have been developed by several other neuroprosthetic companies. Image and figure caption were taken from Ref. [16]. B. New two-shank AMI array that will be implanted into the auditory midbrain in five deaf patients for a clinical study funded by the National Institutes of Health [14]. Each shank consists of 11 platinumeiridium ring electrodes with one of those electrodes near the Dacron mesh for activating outer midbrain neurons to treat tinnitus [23]. A stainless steel stylet is positioned through the center of each silicone array to enable insertion into the brain and is removed after array placement. The Dacron mesh prevents over-insertion of the array and stabilizes the shank within the brain. C. AMI stimulator that will be implanted in a bony bed on the skull underneath the skin and behind the ear area. It uses inductively coupled coils for communication and power transfer with a transmitter device placed on the skin surface. The stimulator and its fast processor is capable of delivering high pulse rates of electrical stimulation (up to 31,500 pps) and recording neural signals on the electrode sites. Images of the AMI array and stimulator were provided by Terry Leer and Jason Leavens from Cochlear Limited.
the auditory portion of the midbrain known as the inferior colliculus. Five patients have been implanted with the single-shank AMI; initial results have been positive in terms of safety and specificity (e.g., systematic and spatially ordered pitch percepts) [12,13]. AMI performance, however, has not yet exceeded that of the ABI and CI. Inaccurate placement of the electrode sites into the target region was also a limitation in that study. Animal, human and cadaver research for improving electrode design, neural targeting and stimulation strategies for the AMI has resulted in a second clinical study funded by the National Institutes of Health to assess the safety and performance of a two-shank version of the device (Fig. 1; [14]). That study is now underway. There remains a sense of uneasiness or doubt surrounding the PABI and AMI. One argument has been that the targeted brain regions are too complex to artificially stimulate neurons and restore performance above what is possible with current implants. That view is reminiscent of the types of comments made against the CI and ABI that were eventually proven wrong. Another concern is related to the surgical risks of implanting penetrating arrays into the brain. Several exciting developments in the field of central neural prostheses, however, provide a more positive perspective on this topic. No one could have imagined 35 years ago that the ABI would be considered safe enough to be implanted into children as young as one year old ([15]; FDA in the United States recently approved children as young as two years). Continuous improvements in surgical techniques and technologies have made this a reality. Significant progress has also occurred for the use of deep brain stimulation (DBS) to treat various neurological and psychiatric conditions, with more than 100,000 patients now implanted with a penetrating DBS array [16]. There are surgical risks with DBS surgery but it isn’t far-fetched to assume that in the future, innovative solutions will bring these complications to nearly zero. Following directly on the heels of the CI recognition in 2013, the LaskerwDeBakey Clinical Medical Research Award this year was given to two more neurostimulation pioneers [17]. Alim Benabid and Mahlon DeLong received the award for their work in developing DBS therapies that reduce tremors and restore motor function in patients with Parkinson’s disease. Thus, for two years in a row,
neural prostheses and brain stimulation have been acknowledged by the Lasker Award Foundation for their impact and benefit to humankind. A recent innovative technology has pushed the field of central neural prostheses even further. A 96-site, threedimensional penetrating array was implanted into the motor cortex in people with tetraplegia to record neural signals and control assistive devices [18], demonstrating that micro-machined, high-density arrays can be safely implanted in the brain and used for restoring function. Considering these monumental achievements, there should be a great sense of optimism toward what is possible with central neural prostheses. Discussions about peripheral versus central implants are also occurring for other sensory modalities. To restore vision, for example, research has focused predominantly on retinal implants since the early 2000s [19,20]. Encouragingly, these implants have enabled patients to achieve shape recognition, pattern orientations, object localization, motion discrimination, and some limited reading capabilities. Visual acuity, however, hasn’t exceeded 20/1260 (legal blindness is 20/200). One major challenge is in positioning enough electrodes within the retina to activate a sufficient number of independent channels of information to the brain. Greater spatial resolution may be achieved using penetrating arrays within the visual regions of the thalamus or cortex, which could also treat a much larger number of blind patients than possible with retinal implants. The surface of the visual cortex was the site for the first visual prosthesis in the early 1970s, however, due to concerns about surgical risks and the complex processing within higher brain centers, there have only been a few groups pushing forward with central visual prostheses. Similar concerns have been expressed toward central somatosensory prostheses [21,22]. Most devices for restoring somatosensation, as part of feedback input for motor prostheses, have focused on stimulating peripheral nerves where it appears that activation of different sites can elicit elementary and distinct tactile and even proprioceptive percepts. For those who cannot use peripheral stimulation such as spinal cord injury patients, more central targets are needed. The somatosensory regions of the thalamus and cortex have both been proposed as potential implant targets. There are questions as to
Editorial / Brain Stimulation 8 (2015) 439e441
whether central brain stimulation will be able to elicit sufficiently simple and distinct types of percepts to be useful for a prosthesis. If anything has been learned from the auditory implant field, it’s that the brain has an incredible ability to take crude and artificial inputs and provide useful sensory function on a daily basis. Not all regions or stimulation patterns will do the job and it will take direct experimentation in human subjects to eventually figure out the right code. But we shouldn’t prematurely doubt the potential of central neural prostheses or the ability to get electrodes safely into appropriate brain regions. After nearly 50 years of exploration with neural prostheses, we have learned that devices can be safely interfaced with the brain and they can restore considerable function, at least for some conditions. With these successes, we can start to change the view of neural prostheses in society from the stuff of science fiction to a daily feature of life, much in the same way that pacemakers and insulin pumps are becoming commonplace. Beyond treatments, there is also untapped knowledge available through these neural prostheses. Recently, there has been significant government support, such as the BRAIN Initiative in the United States or the Human Brain Project in Europe, to better understand the human brain with a long-term goal of improving clinical treatments. Animal studies and computational models provide pathways towards achieving this goal. With so many people being implanted with neural devices in different parts of the brain, however, we have a unique opportunity to study brain function directly in humans, either in those with implants or during intraoperative procedures. As more children and infants are implanted with brain devices, we can also study the development and plasticity of the younger brain in ways not previously possible. This potentially groundbreaking human research will require a transdisciplinary effort spanning academia, clinics, industry and government to build the scientific, technological and regulatory infrastructure to ensure a safe and successful outcome. The time is right and the opportunity is within our reach. It will be exciting to see what the next 50 years has in store for us as we continue to pursue leading-edge research and innovate new technologies, maintaining the enduring optimism that got us here in the first place and that will take us to the next frontier of neural prosthesis exploration. Hubert H. Lim* Department of Biomedical Engineering, University of Minnesota, 312 Church Street S.E., NHH 7-105, Minneapolis, MN 55455, USA Department of Otolaryngology, Head and Neck Surgery, University of Minnesota, 516 Delaware Street S.E., PWB 8A, Minneapolis, MN 55455, USA Robert V. Shannon Department of Otolaryngology, University of Southern California, 806 W. Adams Blvd., Los Angeles, CA 90007, USA
441 * Corresponding
author. Tel.: þ1 612 626 4565; fax: þ1 612 626 6583. E-mail address: [email protected]
Available online 22 November 2014
References [1] Colletti L, Shannon RV, Colletti V. The development of auditory perception in children after auditory brainstem implantation. Audiol Neurotol 2014;19: 386e94. [2] Schwartz MS, Otto SR, Shannon RV, Hitselberger WE, Brackmann DE. Auditory brainstem implants. Neurotherapeutics 2008;5:128e36. [3] Sennaroglu L, Ziyal I. Auditory brainstem implantation. Auris Nasus Larynx 2012;39:439e50. [4] Eisenberg LS, The contributions of William F. House to the field of implantable auditory devices, Hear Res (in press). [5] Colletti L, Shannon R, Colletti V. Auditory brainstem implants for neurofibromatosis type 2. Curr Opin Otolaryngol Head Neck Surg 2012;20:353e7. [6] Matthies C, Brill S, Varallyay C, et al. Auditory brainstem implants in neurofibromatosis type 2: Is open speech perception feasible? J Neurosurg 2014;120: 546e58. [7] LaskerwDeBakey Clinical Medical Research Award 2013. URL: http://www. laskerfoundation.org/awards/2013_c_description.htm; Accessed 22.10.14. [8] Mudry A, Mills M. The early history of the cochlear implant: a retrospective. JAMA Otolaryngol Head Neck Surg 2013;139:446e53. [9] Eisen MD. Djourno, Eyries, and the first implanted electrical neural stimulator to restore hearing. Otol Neurotol 2003;24:500e6. [10] Friesen LM, Shannon RV, Baskent D, Wang X. Speech recognition in noise as a function of the number of spectral channels: comparison of acoustic hearing and cochlear implants. J Acoust Soc Am 2001;110:1150e63. [11] Otto SR, Shannon RV, Wilkinson EP, et al. Audiologic outcomes with the penetrating electrode auditory brainstem implant. Otol Neurotol 2008;29: 1147e54. [12] Lim HH, Lenarz M, Joseph G, Lenarz T. Frequency representation within the human brain: stability versus plasticity. Sci Rep 2013;3:1474. [13] Lim HH, Lenarz M, Lenarz T. Auditory midbrain implant: a review. Trends Amplif 2009;13:149e80. [14] Lim HH, Lenarz T, Patrick J. Phase I safety study for a new two-shank auditory midbrain implant. 2014. NIH Project Number: 1U01DC013030e01A1. NIH Reporter, http://projectreporter.nih.gov/reporter.cfm. [15] Sennaroglu L, Colletti V, Manrique M, et al. Auditory brainstem implantation in children and non-neurofibromatosis type 2 patients: a consensus statement. Otol Neurotol 2011;32:187e91. [16] Johnson MD, Lim HH, Netoff TI, et al. Neuromodulation for brain disorders: challenges and opportunities. IEEE Trans Biomed Eng 2013;60:610e24. [17] LaskerwDeBakey Clinical Medical Research Award 2014. URL: http://www. laskerfoundation.org/awards/2014_c_description.htm; Accessed 22.10.14. [18] Hochberg LR, Bacher D, Jarosiewicz B, et al. Reach and grasp by people with tetraplegia using a neurally controlled robotic arm. Nature 2012;485:372e5. [19] Lorach H, Marre O, Sahel JA, Benosman R, Picaud S. Neural stimulation for visual rehabilitation: advances and challenges. J Physiol Paris 2013;107: 421e31. [20] Shepherd RK, Shivdasani MN, Nayagam DA, Williams CE, Blamey PJ. Visual prostheses for the blind. Trends Biotechnol 2013;31:562e71. [21] Weber DJ, Friesen R, Miller LE. Interfacing the somatosensory system to restore touch and proprioception: essential considerations. J Mot Behav 2012;44:403e18. [22] Bensmaia SJ, Miller LE. Restoring sensorimotor function through intracortical interfaces: progress and looming challenges. Nat Rev Neurosci 2014;15: 313e25. [23] Offutt SJ, Ryan KJ, Konop AE, Lim HH. Suppression and facilitation of auditory neurons through coordinated acoustic and midbrain stimulation: Investigating a deep brain stimulator for tinnitus. J Neural Eng 2014;11:066001. [24] Atencio CA, Shih JY, Schreiner CE, Cheung SW. Primary auditory cortical responses to electrical stimulation of the thalamus. J Neurophysiol 2014;111: 1077e87. [25] Otto KJ, Rousche PJ, Kipke DR. Microstimulation in auditory cortex provides a substrate for detailed behaviors. Hear Res 2005;210:112e7.
Contents lists available at ScienceDirect
Brain Stimulation journal homepage: www.brainstimjrnl.com
Editorial
Two Laskers and Counting: Learning From the Past Enables Future Innovations With Central Neural Prostheses
Andreas is a young boy who was born deaf. Since he has no auditory nerves, he could not benefit from a cochlear implant (CI). A CI is surgically placed in the cochlea and sends electrical currents to surrounding auditory nerve fibers to elicit hearing sensations. When Andreas was three years old, he received an auditory brainstem implant (ABI) [1]. The ABI is similar to a CI but consists of an electrode array that is placed on the surface of the auditory portion of the brainstem. Today, Andreas is 10 years old and can understand speech well enough to attend school with his normal hearing peers. He is even starting to learn to play the guitar. This remarkable case is one of many that show how electrical stimulation of the brain can restore function. Like many innovations, however, the ABI was met with skepticism and low expectations during its development. There were doubts that the complicated circuitry of the brainstem could be artificially stimulated to restore useful hearing and whether the ABI would be successful in children. Since 1979, visionaries such as William House, William Hitselberger, Douglas McCreery and Vittorio Colletti, pushed forward through these hurdles [2e4]. It is now clear that we underestimated the ability of the brain to adapt to a highly non-normal pattern of neural activation from an ABI [5,6]. More than 1200 deaf people, including children as young as one year, have been implanted with the ABI. Many are able to understand speech and talk on the telephone. History seems to find a way of repeating itself. Before the ABI, a similar type of premature skepticism plagued the CI through its development from the 1960s [7]. Numerous clinicians and scientists, including those who studied the microstructure and physiology of the auditory system, could not believe that any useful hearing would result from the crude activation of peripheral neurons by a small number of electrodes. Regardless, pioneers in the field continued to innovate and develop their ideas that eventually led to the CI, one of the most successful neural prostheses to date. More than 300,000 individuals, including infants younger than a year, have been safely implanted with a CI. Many of these individuals can converse almost normally and have been able to integrate into mainstream society. This is a level of performance that was unthinkable 30 years ago. To recognize this phenomenal achievement, three pioneers who were critical to the success of the CI e Graeme Clark, Ingeborg Hochmair, and Blake Wilson e were awarded the prestigious LaskerwDeBakey Clinical Medical Research Award in 2013 [7]. Support from companies and the government, in addition to the work of several other visionaries such as André Djourno, William House and Blair Simmons, helped catalyze and translate the CI from a disputed concept to a daily reality [8,9]. http://dx.doi.org/10.1016/j.brs.2014.10.016 1935-861X/Ó 2015 Elsevier Inc. All rights reserved.
The success of auditory prostheses contains an important lesson for restoration of function through neural prostheses. The brain has an immense capability to process crude forms of information to make meaningful percepts and actions. This doesn’t mean that any type of input or cues will be effective. For CIs, it took several iterations of stimulation strategies to find patterns that reduced channel interaction and appropriately activated neurons to enable speech perception. The point is that the complexity of the brain shouldn’t be the argument against a neural prosthesis, whether a peripheral or central device. With more advanced technologies that allow for a higher number of closely spaced electrodes in three-dimensional configurations and smart algorithms (e.g., allowing patients to optimize their device based on perceptual and/or neural feedback), there will be greater opportunities to find the “right code” for implementation. So what is next for the auditory implant field? The CI and ABI have both achieved performance levels beyond expectations; however, not all implant users sufficiently benefit from these devices. Most CI and nearly all ABI patients also have poor hearing capabilities in noisy environments and for more complicated inputs such as music or multiple people conversing simultaneously. One major limitation in achieving higher performance appears to be the limited number of independent information channels possible with these implants [10]. The CI sends current through a bony modiolar wall of the cochlea with scattered flow of electrical charge to a variable distribution and reduced number of auditory neurons associated with deafness. The ABI is placed on the surface of the brainstem, resulting in high stimulation levels and large current spread to activate auditory neurons within deeper regions. There are several new directions in the auditory field that have sought to increase the specificity of activation with central neural prostheses, using penetrating electrode arrays within the brainstem, midbrain, thalamus or cortex (e.g., [11,13,24,25]). Two types of these neural prostheses have been investigated in clinical trials. A penetrating ABI (PABI) with tip electrodes on 8 or 10 shanks has been developed and implanted into the auditory brainstem of 10 patients [11]. Encouragingly, the PABI could be safely implanted and stimulated in humans and has achieved greater specificity and lower thresholds of activation than the ABI. The performance, however, has not yet exceeded that of the ABI and CI. Inaccurate placement of electrode sites into the target region was a possible limitation in that study. Another neural prosthesis being explored is the auditory midbrain implant (AMI), which consists of one or two shanks with up to 22 electrode sites that are inserted into
440
Editorial / Brain Stimulation 8 (2015) 439e441
Figure 1. A. Simplified schematic of the brain showing the location of electrode arrays currently implanted in humans for restoring hearing or suppressing tinnitus. The CI, ABI, PABI, and AMI are example arrays developed by Cochlear Limited (N.S.W., Australia) and the cortical implant is an example array developed by St. Jude Medical (TX, USA). Similar types of devices have been developed by several other neuroprosthetic companies. Image and figure caption were taken from Ref. [16]. B. New two-shank AMI array that will be implanted into the auditory midbrain in five deaf patients for a clinical study funded by the National Institutes of Health [14]. Each shank consists of 11 platinumeiridium ring electrodes with one of those electrodes near the Dacron mesh for activating outer midbrain neurons to treat tinnitus [23]. A stainless steel stylet is positioned through the center of each silicone array to enable insertion into the brain and is removed after array placement. The Dacron mesh prevents over-insertion of the array and stabilizes the shank within the brain. C. AMI stimulator that will be implanted in a bony bed on the skull underneath the skin and behind the ear area. It uses inductively coupled coils for communication and power transfer with a transmitter device placed on the skin surface. The stimulator and its fast processor is capable of delivering high pulse rates of electrical stimulation (up to 31,500 pps) and recording neural signals on the electrode sites. Images of the AMI array and stimulator were provided by Terry Leer and Jason Leavens from Cochlear Limited.
the auditory portion of the midbrain known as the inferior colliculus. Five patients have been implanted with the single-shank AMI; initial results have been positive in terms of safety and specificity (e.g., systematic and spatially ordered pitch percepts) [12,13]. AMI performance, however, has not yet exceeded that of the ABI and CI. Inaccurate placement of the electrode sites into the target region was also a limitation in that study. Animal, human and cadaver research for improving electrode design, neural targeting and stimulation strategies for the AMI has resulted in a second clinical study funded by the National Institutes of Health to assess the safety and performance of a two-shank version of the device (Fig. 1; [14]). That study is now underway. There remains a sense of uneasiness or doubt surrounding the PABI and AMI. One argument has been that the targeted brain regions are too complex to artificially stimulate neurons and restore performance above what is possible with current implants. That view is reminiscent of the types of comments made against the CI and ABI that were eventually proven wrong. Another concern is related to the surgical risks of implanting penetrating arrays into the brain. Several exciting developments in the field of central neural prostheses, however, provide a more positive perspective on this topic. No one could have imagined 35 years ago that the ABI would be considered safe enough to be implanted into children as young as one year old ([15]; FDA in the United States recently approved children as young as two years). Continuous improvements in surgical techniques and technologies have made this a reality. Significant progress has also occurred for the use of deep brain stimulation (DBS) to treat various neurological and psychiatric conditions, with more than 100,000 patients now implanted with a penetrating DBS array [16]. There are surgical risks with DBS surgery but it isn’t far-fetched to assume that in the future, innovative solutions will bring these complications to nearly zero. Following directly on the heels of the CI recognition in 2013, the LaskerwDeBakey Clinical Medical Research Award this year was given to two more neurostimulation pioneers [17]. Alim Benabid and Mahlon DeLong received the award for their work in developing DBS therapies that reduce tremors and restore motor function in patients with Parkinson’s disease. Thus, for two years in a row,
neural prostheses and brain stimulation have been acknowledged by the Lasker Award Foundation for their impact and benefit to humankind. A recent innovative technology has pushed the field of central neural prostheses even further. A 96-site, threedimensional penetrating array was implanted into the motor cortex in people with tetraplegia to record neural signals and control assistive devices [18], demonstrating that micro-machined, high-density arrays can be safely implanted in the brain and used for restoring function. Considering these monumental achievements, there should be a great sense of optimism toward what is possible with central neural prostheses. Discussions about peripheral versus central implants are also occurring for other sensory modalities. To restore vision, for example, research has focused predominantly on retinal implants since the early 2000s [19,20]. Encouragingly, these implants have enabled patients to achieve shape recognition, pattern orientations, object localization, motion discrimination, and some limited reading capabilities. Visual acuity, however, hasn’t exceeded 20/1260 (legal blindness is 20/200). One major challenge is in positioning enough electrodes within the retina to activate a sufficient number of independent channels of information to the brain. Greater spatial resolution may be achieved using penetrating arrays within the visual regions of the thalamus or cortex, which could also treat a much larger number of blind patients than possible with retinal implants. The surface of the visual cortex was the site for the first visual prosthesis in the early 1970s, however, due to concerns about surgical risks and the complex processing within higher brain centers, there have only been a few groups pushing forward with central visual prostheses. Similar concerns have been expressed toward central somatosensory prostheses [21,22]. Most devices for restoring somatosensation, as part of feedback input for motor prostheses, have focused on stimulating peripheral nerves where it appears that activation of different sites can elicit elementary and distinct tactile and even proprioceptive percepts. For those who cannot use peripheral stimulation such as spinal cord injury patients, more central targets are needed. The somatosensory regions of the thalamus and cortex have both been proposed as potential implant targets. There are questions as to
Editorial / Brain Stimulation 8 (2015) 439e441
whether central brain stimulation will be able to elicit sufficiently simple and distinct types of percepts to be useful for a prosthesis. If anything has been learned from the auditory implant field, it’s that the brain has an incredible ability to take crude and artificial inputs and provide useful sensory function on a daily basis. Not all regions or stimulation patterns will do the job and it will take direct experimentation in human subjects to eventually figure out the right code. But we shouldn’t prematurely doubt the potential of central neural prostheses or the ability to get electrodes safely into appropriate brain regions. After nearly 50 years of exploration with neural prostheses, we have learned that devices can be safely interfaced with the brain and they can restore considerable function, at least for some conditions. With these successes, we can start to change the view of neural prostheses in society from the stuff of science fiction to a daily feature of life, much in the same way that pacemakers and insulin pumps are becoming commonplace. Beyond treatments, there is also untapped knowledge available through these neural prostheses. Recently, there has been significant government support, such as the BRAIN Initiative in the United States or the Human Brain Project in Europe, to better understand the human brain with a long-term goal of improving clinical treatments. Animal studies and computational models provide pathways towards achieving this goal. With so many people being implanted with neural devices in different parts of the brain, however, we have a unique opportunity to study brain function directly in humans, either in those with implants or during intraoperative procedures. As more children and infants are implanted with brain devices, we can also study the development and plasticity of the younger brain in ways not previously possible. This potentially groundbreaking human research will require a transdisciplinary effort spanning academia, clinics, industry and government to build the scientific, technological and regulatory infrastructure to ensure a safe and successful outcome. The time is right and the opportunity is within our reach. It will be exciting to see what the next 50 years has in store for us as we continue to pursue leading-edge research and innovate new technologies, maintaining the enduring optimism that got us here in the first place and that will take us to the next frontier of neural prosthesis exploration. Hubert H. Lim* Department of Biomedical Engineering, University of Minnesota, 312 Church Street S.E., NHH 7-105, Minneapolis, MN 55455, USA Department of Otolaryngology, Head and Neck Surgery, University of Minnesota, 516 Delaware Street S.E., PWB 8A, Minneapolis, MN 55455, USA Robert V. Shannon Department of Otolaryngology, University of Southern California, 806 W. Adams Blvd., Los Angeles, CA 90007, USA
441 * Corresponding
author. Tel.: þ1 612 626 4565; fax: þ1 612 626 6583. E-mail address: [email protected]
Available online 22 November 2014
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