A, whole-cell currents elicited by 10 μM NMDA before and shortly after a 600 ms light pulse. Filters allowing wavelengths longer than 280 nm (n = 9), 324 nm (n = 9), 475 nm (n = 5) and 610 nm (n = 5) were placed in the path of the light reaching the cells. Scale bars: 250 pA, 1 s. B, whole-cell currents measured in a neurone in response to 10 μM NMDA before and shortly after a 60 s exposure to light using a filter that allows wavelengths longer than 385 nm to reach the cell. Scale bars: 250 pA, 0.5 s.