The Human Brain Project is Europe’s flagship contribution to neuroscience. Established last year and funded by the European Commission, the project was meant to rally scientists and computer engineers around developing better tools to study how the brain works.

But its most ambitious goal — a computer simulation of the entire brain — came under attack on Monday when hundreds of neuroscientists from around the world sent an open letter to the commission condemning what they see as an absence of feasibility and transparency.

The letter said that the project’s “overly narrow approach” threatened to set Europe back in terms of its scientific progress and its investment, about $130 million a year over the next 10 years.

“It’s like a moonshot, but before we knew how to build an airplane,” said Zachary Mainen, a neuroscientist at the Champalimaud Center for the Unknown, in Lisbon, and an author of the letter. “We can’t simulate the 302 neurons in a nematode brain. It’s a bit premature to simulate the 100 billion neurons in a human brain.”