Officials from the Group of Seven rich democracies convened some of the world's best-known economists for a brainstorming session on how to keep the global upswing going.

The meeting of finance ministers and central bank officials in Dresden is taking place amid concern that recoveries in Europe and the United States face obstacles before they become truly broad and self-sustaining.

Worries include volatility in stock and bond markets and a lack of investment by governments and businesses in new projects.

The ministers heard views Thursday from former U.S. Treasury Secretary Larry Summers, who has warned that weak investment could lead to long-term stagnation, and Robert Shiller of Yale University, who has studied speculative market booms, among others.

The G-7 includes: Britain, Canada, France, Germany, Japan, Italy, and the U.S.