Understanding the Brain

Our picture of the brain has changed markedly since antiquity, when it was considered an organ of minor importance. This lecture traces the major paradigm shifts in our understanding of the brain and the contributions of such pioneers as Leonardo da Vinci, René Descartes, and Thomas Willis, the "father of neurology."

This lecture covers the overall organization of the brain and spinal cord and defines important terms and concepts, focusing on areas of the central nervous system that can be viewed from the outside. Neuroanatomists divide the brain into five major regions from rostral (front) to caudal (back).

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).

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.

The cerebral cortex is the outer layer of neurons or "bark" covering the brain. Considered the seat of the mind, it is where cognition and other higher-order functions such as language, intellect, and memory take place. The cortex can be divided into four lobes, each comprised of areas that are associated with specific functions.

This lecture introduces the traditional and modern classification of sensory, motor, and association cortex. One of the crucial discoveries of the past 40 years is that much of what was previously called association cortex is actually sensory in function. For example, there are many more cortical areas devoted to vision than previously thought.

We investigate how the brain's subdivisions and different cell types are generated during the remarkable process of development. From a few cells, a human brain forms that is capable of regulating the function of all the other organs as well as producing a theory of relativity or appreciating Bach.

This lecture focuses on the structural and functional differences between the two main types of cells in the central nervous system: neurons and glial cells. The name glia ("glue") derives from the historical view that glia simply hold the brain together, but modern neuroscience has revealed that these cells have many other functions.

Unlike most cells in the body, neurons are designed to receive and transmit information. How do they do it? The critical factor is the internal and external environment of neurons, where changes in the distribution of ions (charged atoms) act as a signaling mechanism for encoding and transmitting information.

Neurotransmitters are specialized chemical messengers that signal activity from one neuron to another. More than 60 neurotransmitters/neuromodulators have been identified, including simple amino acids like glutamate; enkephalins and endorphins, which are involved in the processing of pain; and dopamine, which plays a role in reward and addiction.

This lecture uses the damage caused by stroke to review material covered up to this point in the course. By understanding the organization of the brain and its blood supply, we can predict which functions will be lost or affected after a stroke impairs the blood flow to specific regions of the brain.

This lecture investigates how the eye works in concert with the brain. Far from taking a picture of the external world, the eye actually transmits information primarily about edges and contrast to the brain. From this limited input, the brain constructs the visual world we experience in all its complexity and detail.

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.

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 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).

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.

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.

Coordination of movement, especially learned, skilled motor movement, is largely under the control of the cerebellum. This "little cerebrum" allows for the proper timing and execution of movement and for the correction of errors during ongoing movement. We could not walk, play, or dance without a cerebellum.

Parkinson's disease arises when neurons are lost from a specific area of the brain called the substantia nigra. This removes a major source of input to forebrain structures involved in regulating movement. This lecture covers signs, symptoms, and treatments of this disorder.

The ability to communicate symbolically through language is thought to be unique to our species. Language involves both higher-order sensory and motor areas of the cerebral cortex. Even though written language is an invention, specific areas in the brain underlie this ability as well.

The limbic system represents a large number of interconnected nuclei that together allow for learning, memory, emotion, and executive function. Its importance is dramatically illustrated by the case of Phineas Gage, a railroad worker in the 1840s whose personality was completely altered by a frontal lobe injury involving part of the limbic system.

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.

Depression is a scourge of modern societies. This lecture focuses on unipolar depression, a central nervous system disorder that has known anatomical and biochemical correlates. We also investigate how the three major classes of antidepressants work and what led to the development of designer antidepressant drugs, such as Prozac.

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.

Psychoactive drugs that produce euphoria or a "high" do so by altering the biochemistry of the endogenous reward system. Such drugs can be both physiologically and psychologically addicting. Using cocaine and marijuana as examples, we investigate how drugs can hijack this system and even produce permanent changes in the brain.