Rapid advances are occurring in neural engineering, bionics and the brain–computerinterface. These milestones have been underpinned by staggering advances in microelectronics, computing, and wireless technology in the last three decades. Severalcortically-based visual prosthetic devices are currently being developed, but pioneeringadvances with early implants were achieved by Brindley followed by Dobelle in the 1960sand 1970s. We have reviewed these discoveries within the historical context of the medicaluses of electricity including attempts to cure blindness, the discovery of the visual cortex,and opportunities for cortex stimulation experiments during neurosurgery. Furtheradvances were made possible with improvements in electrode design, greater understanding of cortical electrophysiology and miniaturisation of electronic components.Human trials of a new generation of prototype cortical visual prostheses for the blindare imminent.
, 1974). The group's tests also exposed a
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Fig. 7 A recipient of the Dobelle implant, rst implanted in 1978. In 2000 his external hardware and software was upgraded, including the miniature glasses-mounted camera shown, greatly enhancing the functionality of his prosthesis. Reproduced from (Dobelle, 2000), with permission. b r a i n r e s e a r c h 1 6 3 0 ( 2 0 1 6 ) 2 0 8 2 2 4 breakdown around the transcutaneous connector and ultimately complete failure of the device (Naumann, 2012). The year after this patient was implanted, Dobelle was conominated along with W.J. Kolff for the 2003 Nobel Prize in Medicine and Physiology (Oakley, 2011b). The following year Dobelle passed away from complications of diabetes. At the behest of his family, the visual prosthesis intellectual property was transferred to Stonybrook University in the state of New York, USA, with research currently ongoing within the university's Department of Biomedical Engineering (Lin, 2006; Naumann, 2012). 3.5. Intracortical electrodes
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While early human studies (o1960s) of cortical stimulation tended to avoid penetrating and therefore damaging the cortex, there are scattered reports of human brain stimulation experiments involving intracortical electrodes (Bartholow, 1874; Peneld, 1947). Button and Putnam described using very thin (76 mm) stainless steel wires implanted in the occipital cortex, with reportedly no complications (Button and Putnam, 1962; Button, 1958). The advantages of intracortical electrodes were not immediately evident in Button and Putnams results. Button stated in 1958 that the keenest ashes of light (Button, 1958, p. 54), which largely consisted of phosphenes lling much of the patients visual eld, were obtained with stimulus currents of 620 mA. Conversely, Doty demonstrated in 1965 that stimulation of intracortical electrodes at currents as low as 50 mA could be detected by trained macaques, who would respond by pressing a lever (Doty, 1965). Moreover, it was shown that the locations of visual p
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, 1968). Nevertheless, a feature common to human visual prosthesis research in the two decades after Button and Putnam was the use of surface stimulating electrodes, which require currents in the order of 0.53 mA to generate phosphenes. The magnitude of current required in these early studies using surface stimulation was also thought to be responsible for the production of multiple phosphenes, a problem that Klomp and Dobelle attempted to address by adding a ground plane to their array. This ran between the electrodes, providing a return path close to the electrodes being stimulated (Dobelle, 2000; Klomp et al., 1977). By 1980, ongoing research had rened the lower limit of stimulus threshold current for intracortical stimulation, which was shown to be
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