When neurobiologists write about the brain, they must refer to specific areas within the brain's tissue. In order to describe locations efficiently, they use a universal terminology. Some easily located parts of the brain are used as reference points, and many different directional terms are used to describe the sought-after part's location relative to one or more reference points. The major terms you will need to know are outlined below.

The cortex of the brain is a thick layer of tissue surrounding the more interior parts of the brain. The cortex lies between the skull and the rest of the brain. Many of the complex functions that the brain performs take place in the cortex. Different sections of the cortex perform different functions. For example, the visual cortex receives and processes signals from the retina on the eye, and the motor cortex drives the body's movement. The cortex contains a large number of connections with itself, with other parts of the brain, and with the body. The cortex is also highly plastic, meaning that the connections it makes can change over time to better accommodate the brain's needs. The cortex can be mapped out into separate areas based on the functions that they perform and the patterns of connections that they make. The rest of the brain is divided into discrete structures that perform separate functions and have more predictable connections with each other. Many of these areas, but not all, perform functions that are more basic, or low-level, than the functions of the cortex. We will examine both cortical areas and non-cortical structures when we study the many functions of the brain.

In biochemistry, having more surface area generally allows reactions to progress faster. Therefore, evolution has designed the brain to maximize the surface area it has available for reactions. The principal way in which it does this is by folding in on itself many times over. When the brain is viewed from the outside, its folds make it look wrinkly. The many extrusions and intrusions that make up these folds are called gyri and sulci. The hills in the surface of the brain are called gyri (singular: gyrus), and the valleys are called sulci (singular: sulcus). Very deep gyri are called fissures. When locations are described in the brain, major sulci and gyri are often used as reference points, like familiar landmarks. The central sulcus is the most well-known of these landmarks--it protrudes into the brain from the top down, in a central location. The lateral fissure, also called the Sylvian fissure, is another common reference point; it cuts into the brain horizontally from the front. We will refer to these points later in the text when mapping out the brain's four lobes.

Because the brain is a relatively small and very compact structure, directions given to describe any one particular area within the brain must be precise. The irregular shape of the brain makes this more complicated, so the normal left, right, up, and down directions are not clear enough. These directions are somewhat difficult to describe in writing, so be sure to refer to the figure below.

The anterior/posterior division is fairly clear. Anterior refers to the front of the brain, while posterior refers to the rear. Superior and inferior also are pretty conventional. Superior is up, while inferior is down. The terms rostral and caudal refer to the longitudinal axis of the forebrain, pictured below. Rostral points toward the front of the brain along this axis, while caudal means toward the back. Dorsal, and ventral refer to that axis and the longitudinal axis of the brainstem and spinal cord. Dorsal refers to anything either above the forebrain axis or to the rear of the brainstem/spinal cord axis. (It might help you remember this if you think of a dolphin's dorsal fin.) Ventral, by contrast, indicates anything either below the forebrain axis or to the front of the brainstem/spinal cord axis. These directions are generally used in the context of statements like "part A is rostral to part B" or "part C is anterior to the Sylvian fissure."

The other three directions, called planes of section, are used when taking slices of the brain for study. Slices are useful for examination under a microscope because they are thin enough to let light through. Sagittal refers to a slice that cuts the brain into a left and a right half. A sagittal slice is the same as looking at the brain from the side. Coronal slices cut the brain into an anterior and a posterior half. A coronal slice is the same as looking at the brain from the front. Horizontal means cutting the brain into a superior and an inferior half. A horizontal slice is the same as looking at the brain from above.