Page 380 - Handbook of Biomechatronics

374 Lilach Bareket et al.

have been generated through cortical stimulation. The results of this study
have not yet been reported in the scientific literature.
Ferrandez et al. (2007) developed a system that includes a transistor-based
current source, a microprocessor circuit with programmable waveforms,
and an array of penetrating electrodes (Utah array). The main advantage
of using a transistor-based stimulator is the very low power consumption.
The current level could be adapted to the different working electrodes
and tissue impedances. The penetrating electrodes were tested in rabbit
cortex and the system was found to be safe, and able to deliver continuous
stimuli during 240h using a 9V battery (Ferrandez et al., 2007). The disad-
vantage of this array is its limited geographic coverage of the visual cortex,
unless multiple arrays can be deployed.
Troyk and coworkers at Illinois Institute of Technology developed a
wireless floating microelectrode array (WFMA), and an image processing
system. In-vivo testing of a 16-channel WFMA was conducted in a rat sciatic
nerve model over a period of 143 days (Bredeson et al., 2015; Romero-
Ortega et al., 2015). Different fascicles of the rat sciatic nerve have been
selectively stimulated and motor evoked potentials remain stable overtime
and nerve stimulation charges were within tissue safety limits. The testing
of these arrays in cerebral cortex has not yet been reported (Bredeson
et al., 2015; Romero-Ortega et al., 2015). An instrument for cortical
implantation procedures in nonhuman primates was also developed
(Tawakol et al., 2016).
The MVG is developing the “Gennaris” device which includes a camera,
a vision processing computer, the electrode interface with the brain, the
interconnecting links (wired and wireless), and the power system. The elec-
trode carrier is a ceramic box containing an ASIC, wireless coil, and 43 Pt-Ir
microelectrodes (2.5mm height and 125μm in diameter), spaced 1mm apart
on a hexagonal grid (Fig. 4A). The electrodes are insulated with Parylene
C and have an annular exposed area on the shaft (Fig. 4B).
Potentially, more than 300 electrodes could be placed in the visual cor-
tex. A pocket-sized vision processor has been developed to run software
algorithms that convert photographic images from a small digital camera
mounted on a spectacle frame into pixelated patterns which represent rele-
vant shapes and contours in the environment. The “transformative reality”
algorithms are similar to those used in robotic vision applications, and are
suitable for such as object recognition and indoor navigation. The system
could potentially enable the recipient to recognize objects, avoid obstacles,
and recognize the outlines of people and their gestures, but the anticipated