The Sensex at the Bombay Stock Exchange gained 40 points or 0.2 percent to 17,979 in early trade today on revival of selective buying by investors. But the Sensex later surrendered all those gains and stood 46 points or 0.3 percent in the red at 17,892 a short while ago.Other Asian bourses in Japan, China, Singapore, Hong Kong, Indonesia, Taiwan and South Korea fell between 0.1 percent and one percent after the US Central Bank cut its GDP growth forecast and China's economic growth slowed.