The sensations produced by electrical stimulation of the visual cortex

Abstract

1. An array of radio receivers, connected to electrodes in contact with the occipital pole of the right cerebral hemisphere, has been implanted into a 52‐year‐old blind patient. By giving appropriate radio signals, the patient can be caused to experience sensations of light (‘phosphenes’) in the left half of the visual field. 2. The sensation caused by stimulation through a single electrode is commonly a single very small spot of white light at a constant position in the visual field; but for some electrodes it is two or several such spots, or a small cloud. 3. For weak stimuli the map of the visual field on the cortex agrees roughly with the classical maps of Holmes and others derived from war wounds. With stronger stimuli, additional phosphenes appear; these follow a map that is roughly the classical map inverted about the horizontal meridian. 4. The phosphenes produced by stimulation through electrodes 2·4 mm apart can be easily distinguished. By stimulation through several electrodes simultaneously, the patient can be caused to see predictable simple patterns. 5. The effects of the duration and frequency of stimulating pulses on the threshold have been explored. 6. For cortical phosphenes there is no sharp flicker fusion frequency, and probably no flicker fusion frequency at all. 7. During voluntary eye movements, the phosphenes move with the eyes. During vestibular reflex eye movements they remain fixed in space. 8. Phosphenes ordinarily cease immediately when stimulation ceases, but after strong stimulation they sometimes persist for up to 2 min. 9. Our findings strongly suggest that it will be possible, by improving our prototype, to make a useful prosthesis.

The optometric correlates of migraine

“…As the spreading oligaemia reaches sensory motor areas of the brain, the patient experiences the focal neurological aura symptoms. The neurological changes during aura parallel what is seen if the brain is directly stimulated (Penfield and Perot, 1963;Brindley and Lewin, 1968) and are also remarkably similar to the changes that would be predicted if ocular dominance columns (Hubel and Weisel, 1968) in the cortex were serially activated. Woods et al (1994) demonstrated a spreading oligaemia directly with a positron emission tomography study.…”

The Dependence of Spectral Impedance on Disc Microelectrode Radius

“…Therefore, a sin wave stimulus delivering the same amount of total charge as a square wave stimulus would likely excite a greater population of cells in the electrode center since it does not consist of the higher order harmonics present in the latter. It is interesting to note that early cortical stimulation studies used sin wave stimuli [24], [25], and it has been shown in isolated retina stimulation that sin wave pulses have a lower threshold for stimulation compared with square wave pulses of the same amplitude [26]. …”

Demonstration of artificial visual percepts generated through thalamic microstimulation

“…Although early attempts at cortical stimulation in humans used relatively large surface electrodes with high current levels (3,6,24), recent approaches achieved far better results with penetrating microelectrodes terminating in cell body layers. Schmidt et al (25) working in human visual cortex stimulated between single microelectrodes and a remote return and reported pinpoints or disks of light (Ϸ1°maximum).…”