The human brain — a spongy, three-pound mass of tissue — is the most complex living structure in the known universe.

Researching the brain and mind requires a major financial investment on a global scale, and takes place in a wide variety of locations and organizations.

Scientists who study the brain do so for many reasons. For some, the opportunity to study the most complex living structure in the known universe is itself an exciting quest. So much is still unknown about brain function and development.

The discovery in the late 1950s that the level of dopamine was decreased in the brains of Parkinson’s patients was followed in the 1960s by successful treatment with the drug levodopa, which is converted to dopamine in the brain. This historical event is one of the greatest medical breakthroughs in the field of neurology.

What do standing frustrated in a supermarket checkout line or sitting in a traffic jam have in common with fleeing predators, as was done in the early days of human beings?

The cerebrum, the largest part of the human brain, is associated with higher order functioning, including the control of voluntary behavior. Thinking, perceiving, planning, and understanding language all lie within the cerebrum’s control.

Optical imaging relies on shining weak lasers through the skull to visualize brain activity. These techniques are inexpensive and relatively portable. They are also silent and safe: Because only extremely weak lasers are used, these methods can be used to study everyone, even infants.

The brain uses a variety of chemicals called neurotransmitters to communicate between brain cells.

Insulation covering wires preserves the strength of the electrical signals that travel through them. The myelin sheath covering axons serves a similar purpose.

Although most of us don’t think of it in this way, the related senses of taste and smell help us interpret the chemical world.