Our brain stores material brought to it from all five of our senses. You can recall, sometimes quite vividly, visual images, sounds, smells, textures, and so on. We know that the richer the experience is in sensory terms, the more easily the brain can store it and recall it later.
The higher education system has traditionally been tailored toward "left brain processing." The left lobe of the brain specializes in activities that are primarily mathematical/verbal, sequentially arranged, and logical--precisely the types of activities that go along with listening in class, reading a textbook, taking notes, and so on.
The processing that is specialized in the right lobe of the brain goes largely unused by most college students in their formal learning experiences. The right side of the brain specializes in activities that are visual and spatial, "holistic," emotional, creative, and intuitive. Many learning theorists believe that most people are inclined to use or are more comfortable using either the right or left side of the brain for some learning activities. It stands to reason (and to intuition!) that learners who actively use both lobes of the brain will be able to learn more easily and develop "richer" mental concepts that the brain should be able to retrieve when it needs to.
Mind maps are tools that you can use when reviewing for a test to take advantage of right-brain processing. A mind map is a device that represents a concept in both verbal and nonverbal terms. It depends on spatial and visual cues that serve as powerful links to aid recall.
This is typical left-brained material: words on the page, read from top to bottom and left to right. How much of the outline can you write below?