Cell . . . The new method is expected to help blind people regain their vision.

Most of the patients with acquired blindness only suffer from eye or optic nerve damage. Therefore, a visual cortical prosthetic (VCP) device bypassing the eye and optic nerve has been developed, which can directly transmit visual information from the camera to the visual cortex.VCP is based on the theory that the electric current in the visual cortex can produce a tiny flash phenomenon.it has been speculated that this flash is similar to the pixels on a computer monitor, and when they are combined together, they produce a coherent image.in the early test of VCP, when stimulating multiple electrodes, only multiple isolated flash phenomena could be perceived, and could not be combined into a coherent image.in 2018, Professor Daniel yoshor and Professor William H. bosking from Baylor Medical College in the United States found the same problem after implanting intracranial electrodes into subjects with normal vision during the preoperative evaluation of epilepsy.on May 14, 2020, Professor yoshor and Professor bosking team continued to work together and published the title "dynamic stiffness of visual cortex products form vision in sighted and blind" in cell magazine Human's research paper, developed a new alternative method to overcome the above problems: by dynamically activating a series of electrodes, the visual cortex surface can be depicted in a coherent shape.in the existing VCP, the electrical stimulation mode similar to multi probe is used: multiple electrodes are stimulated at one time or there is only a small deviation in time, which leads to the incoherent perceptual information (Fig. 1c).the new model applied by the team is to stimulate the electrodes in a dynamic way to form the letter "Z" on the surface of the cortex (Fig. 1D).in fact, it's the same as writing on the palm of your hand.if you just press multiple points on your palm, it's hard to think of it as a coherent shape (Fig. 1a), while moving a pressing point dynamically can make us feel the shape of "Z" (Fig. 1b).these electrodes that sense dynamic stimuli are located in discrete locations, and additional technical means are needed to convert these dynamic stimuli into a trajectory that can continuously stimulate the cerebral cortex.this technology is called current guiding: if the current flows through two adjacent electrodes, a virtual electrode is created between them.by changing the amount of current transferred between the two electrodes, the virtual electrode can be positioned in different positions along the line segment between the two electrodes.Figure 1 in the team's study, they implanted electrodes into the medial wall of the occipital lobe near the talform sulcus in a blind person, that is, the primary visual cortex.then a 100 millisecond electrical pulse containing 60Hz is transmitted to two nearby electrodes, producing five different levels of current transmitted to each electrode.at the first stimulus level, a 100 millisecond pulse sequence and a 3.6 Ma base current were transmitted to the electrode F01 near the front end, while no current was transmitted to electrode F03 (recording f01:100%, f03:0%). During this process, participants 03-281 reported a single flash located at the upper right of the visual field and recorded its position on the touch screen.after repeated ten times, the average position was 13.3 in azimuth, 2.1 in elevation (center position: 13.3, 2.1), and dispersion (1.0, 0.5).at the fifth stimulation level, 4mA current was transferred to the back end electrode F03, but no current was transmitted to electrode F01 (F01: 0%, F03: 100%); central position: 5.4, 2.2; dispersion: 0.9, 0.6.consistent with the known retinal pigment tissue of visual cortex, F03 flashed closer to the center than F01.but under the condition of intermediate horizontal current stimulation, the current is transferred to the two electrodes in different proportions. The purpose is to create a virtual electrode between the two physical electrodes by using current guided technology.at the second stimulation level, F01: 80%, F03: 50%; central position: 11.4, 2.1; dispersion: 0.5, 0.3.at the third stimulus level, F01: 70%, F03: 70%; central position: 9.8, 2.1; dispersion: 0.4, 0.3; at the fourth stimulation level, F01: 50%, F03: 80%; central position: 8.0, 2.2; dispersion: 0.5, 0.3.the current stimulation of 120Hz pulse current first increased and then decreased along the five electrode positions in the front and back of the cerebral lingual gyrus can generate the virtual electrode moving forward and backward along the gyrus.the subjects indicated that 80% of them (up to 10%) felt like a line as shown in Figure 2.Figure 2 when the researchers found that the use of dynamic stimulation can create letter perception in subjects with normal vision, they implanted five electrodes into the inner wall of the visual cortex of blind subjects. After stimulating each electrode separately, each electrode produced a kind of scattered flash.by tracking the flash pattern of each electrode, seven different dynamic stimulus sequences produce corresponding seven letter like shapes.through association and multi-dimensional scaling and K-means clustering, the researchers quantified the letter shape corresponding to each dynamic stimulus.it is only necessary to change the order of stimulating electrodes in the body of blind subjects to perceive various letter shapes and draw and distinguish these letter shapes reliably.the biggest difference between dynamic current stimulation and previous visual perception research of current stimulation is that a series of current stimuli are related to the perceptual shape transmitted to the subjects, but do not follow a fixed order.in the past, when multiple electrodes are stimulated at one time, the generated flash will interact with each other, and will often gather into a flash of unrecognized shape.and the dynamic stimulation current can avoid this kind of situation, thus improving the effective spatial resolution of the generated patterns.the combination of dynamic stimulation current and dynamic current control with new high-density electrode network electrical stimulation can help blind people recover useful visual function and conduct information conversion more effectively in other VCP applications.original link: plate maker: Ke