Gene therapy for color blindness near 530 nm, and the S cone absorbs near 420 nm. Contrary to popular belief, the peak absorption frequency for L, M, and S cones do not exactly correspond to red, green, and blue wavelength. Rather, the peak frequency for the L cone is orange, yellowish green in M cones, and blue-violet in S cones. These cones transduce the absorbed light into electrical information to be relayed to neurons in the retina such as retinal bipolar cells and retinal ganglion cells, before reaching the brain. The signals from different cones are added or subtracted from each other to process the
Electrical brain stimulation physician Luigi Galvani (1737–1798) that nerves and muscles were electrically excitable. The stimulation of the surface of the cerebral cortex by using brain stimulation was used to investigate the motor cortex in animals by researchers such as Eduard Hitzig (1838–1907), Gustav Fritsch (1838–1927), David Ferrier (1842–1928) and Friedrich Goltz (1834–1902). The human cortex was also stimulated electrically by neurosurgeons and neurologists such as Robert Bartholow (1831–1904) and Fedor Krause (1857–1937). In the following century, the technique was improved by the invention of the stereotactic method by British neurosurgeon pioneer Victor Horsley (1857–1916), and by the development of chronic electrode implants