Like the slap of a white glove across the cheek, the onslaught of top-notch British groups demands an American response. The Brains might well be the designated defenders of U.S. honor in the lofts and Art Deco dance palaces of progressive rock. From Atlanta, they graft cerebral guitar and synthesizer textures from the newest New Wave onto a thumping, made-in-U.S.A. hard rock. The Brains, last year's debut album, won the critics with its heavy-metal pyrotechnics, druggy moods and brighter-than-average lyrics. Electronic Eden's livelier tempos and more adroit hooks (check out Dream Life, for instance) suggest that the Brains won't be stuck noodling in an ivory tower.