Exploring top-down visual pathways using micro-stimulation and its applications to cortical visual prosthesis

The search for restoring vision has focused on retinal implants or cortical implants. The latter approach has mostly focused on the stimulation of feedforward visual pathways, involving primary visual areas such as V1 and V2. These results have given us the perception of dots of light known as phosphenes, but not the complexity of natural visual perception. This is likely because visual perception is a widespread computation in the brain. Key areas that contribute to vision include higher-order visual areas such as V4, which integrates feedforward and top-down information, as well as high-order cognitive areas such as the prefrontal cortex (PFC), which controls top-down modulation such as visual attention. This work will focus on the stimulation of PFC and its effects on V4. Most precisely, on the application that such an interaction might bring to the field of visual prosthesis. We found mild but distinct effects of different PFC stimulation patterns on V4 responses, as expected from top-down mudulatory effects. This offers promissing results for future integration of this pathway in future visual neuroprosthetic devices to achieve a more holistic sense of vision. In the introduction we will revise the historical factors that lead researchers to focus on the visual cortex as the primary target for visual neuroprosthetics. To conclude, we will present our position on the current state of prosthesis and debate whether we could already use current neurotechnologies, albeit imperfect, to benefit blind people. 

”XVII. Men ought to know that from the brain, and from the brain only, arise our pleasures, joys, laughter and jests, as well as our sorrows, pains, griefs and tears. Through it, in particular, we think, see, hear, and distinguish the ugly from the beautiful, the bad from the good, the pleasant from the unpleasant, in some cases using custom as a test, in others perceiving them from their utility. It is the same thing which makes us mad or delirious, inspires us with dread and fear, whether by night or by day, brings sleeplessness, inopportune mistakes, aimless anxieties, absentmindedness, and acts that are contrary to habit. These things that we suffer all come from the brain, when it is not healthy, but becomes abnormally hot, cold, moist, or dry, or suffers any other unnatural affection to which it was not accustomed. Madness comes from its moistness. When the brain is abnormally moist, of necessity it moves, and when it moves neither sight nor hearing are still, but we see or hear now one thing and now another, and the tongue speaks in accordance with the things seen and heard on any occasion. But all the time the brain is still a man is intelligent.” Hyppocrates, Sacred Disease, 400 B.C.