The brain is an extraordinarily intricate web of one hundred billion neurons. Somehow through the trillions of connections among these neurons, the phenomenon of the human mind emerges. Do we know how the mind comes out of the brain? Yes and no. We are learning more and more about what we call the neurobiological substrates or correlates of mental life. We are learning which parts of the brain are active when we do various mental functions. But correlation is not equal to causation. Just because two things happen together does not mean that we understand how one thing causes the other. The fundamental mystery of how billions of mindless brain cells, or neurons, somehow come together to create consciousness continues to elude us.

The concept of qualia relates to the question of subjectivity—what is the yellow of yellow, the green of green? Although we know a tremendous amount about how the brain processes light waves, we still have no idea how our own experience of yellow comes to be. At present, many neuroscientists have agreed to put the question of qualia aside. By studying how different brain processes correlate with various mental processes, we can still learn an inordinate amount about the relationship of brain and mind. This next section addresses what we do know about the links between the mind and the brain.