The Allen Institute for Brain Science announced Wednesday that Microsoft Corp. co-founder Paul G. Allen had donated $300 million to launch an effort to map the brain's basic circuitry of perception.

Doubling its staff of scientists and technicians to more than 350 people, the Seattle-based nonprofit group plans to build over the coming decade a series of "brain observatories," computational tools to map neural behavior. The aim is to systematically explore the roots of vision and decision-making by analyzing the billions...