This lecture discusses some of the neurotransmitters that are critical in the normal functioning of the limbic system circuits. Damage to this system can cause the delicate balance of excitation and inhibition to be disrupted. Such imbalances are believed to underlie many mental disorders such as depression.

All humans seek experiences that are rewarding or pleasurable. This lecture covers the brain structures and neurotransmitters involved in reward - in functions as diverse as slaking thirst or enjoying a sunset. The endogenous reward system allows us to tap into the joy of life and engage in the world.

Like seeing, hearing is a construction of the brain. This lecture discusses how the ear converts pressure waves in the air into electrical signals that travel to the auditory areas of the brain, where they are interpreted as sound. We don't just "hear" sounds; we apply meaning to them, as in our processing of language.

The hundreds of nuclei in the brain can be grouped into specialized systems for sensation, learning, memory, and other functions. Regions of white matter can also be subdivided into functional types; for example, projection pathways connect different areas, like the motor cortex and the spinal cord.

We trace pathways from the retina of the eye to different areas in the cortex, where functions such as face recognition and color perception take place. Color is a fascinating example of how "seeing" is a mental construct; color is not a property of objects in the world but rather a consequence of brain processes.

Not only do we experience the world, we move around in it. This lecture covers the pathways and brain areas that allow us to make voluntary movements of the body. The motor system is divided into pyramidal, extrapyramidal, and cerebellar subsystems, which work together in normal movement.

The somatosensory system gives us information not only about the immediate external world but also about our own bodies. From receptors in our skin, joints, and other parts of our bodies, parallel pathways transmit information that we experience as the senses of touch, pain, temperature, and proprioception (awareness of where our limbs are).

We examine how the central nervous system is organized internally, starting with the basic unit: the nerve cell or neuron. The brain and spinal cord are made up of concentrations of neuronal cell bodies called nuclei (gray matter) and bundles of axons coursing between them (white matter).

Agnosia ("without knowledge") is the inability of individuals to recognize some aspect of their sensory experience because of lesions in the brain. This lecture concentrates on visual agnosias, where an individual who can see loses some specific knowledge related to vision, such as the ability to identify faces or to distinguish between stationary and moving objects.

Why do we sleep? What, if anything, do dreams mean? Far from being a passive event, sleep is actively induced and involves areas of the central nervous system extending from the spinal cord to the forebrain. Researchers have also learned a great deal about the types of dreams that occur during various stages of sleep.