By Catherine A. Sanderson, Amherst College
The brain is divided into three major sections: the hindbrain, the midbrain, and the forebrain. The hindbrain directs basic processes that we need to survive—respiration, heart rate, and arousal. The midbrain regulates our movements and helps orient our eyes and bodies to both visual and auditory information in the world. The forebrain controls our thoughts, motivations, and emotions.
The Hindbrain
The hindbrain is the part of the brain directly above the spinal cord. It consists of three separate parts: the medulla, which is essentially an extension of the spinal cord and conveys messages to and from the brain; the pons, which carries information between several areas of the brain, such as between upper and lower parts of the brain; and the cerebellum, which controls fine muscle movement and balance.
The Midbrain
The second major part of the brain is the midbrain, which is located above the hindbrain. Running through the hindbrain and midbrain is a network of neurons called the reticular formation that maintains consciousness, regulates behavioral arousal, and alerts other parts of the brain to important events. Because of its control over basic processes necessary for survival, damage to this part of the brain is instantly fatal.
The midbrain contains a small structure known as the substantia nigra that secretes dopamine, a neurotransmitter. Parkinson’s disease, a progressive disorder causing problems with movement and balance, develops when cells in this part of the brain begin to die, leading to a loss of dopamine, which in turn causes problems with movement.
This article comes directly from content in the video series Introduction to Psychology. Watch it now, on Wondrium.
The Forebrain
The forebrain is the largest major part of the brain. It is involved in complex emotional, cognitive, and behavioral processes: body weight, emotions, sex drive, and so on. It includes four key structures: the limbic system, the thalamus, the hypothalamus, and the cerebral cortex.
Each of these plays a distinctive role in making us who we are and in what makes us unique and different from other people.
The Limbic System
The limbic system is an interconnected group of structures, including the amygdala and hippocampus, that is generally responsible for emotions and memory.
The amygdala processes emotions and, in particular, fear. A fascinating study comparing brain scans of people in prison for committing murder to brain scans of people of same age and background but not in prison found that this part of the brain was about 18% smaller for those convicted of murder.
This finding suggests that people who commit murder may not experience the same feelings of remorse and guilt that other people do, which of course may make it easier to commit this sort of crime. They also may not have the same fear of consequences, such as spending the rest of their life in prison.
On a more positive note, a study of brain activity in people who had engaged in a quite extraordinary act of generosity—like donating a kidney to a total stranger—revealed nearly the opposite finding. The donors’ amygdala was found to be 8% larger than it is in most people.
The hippocampus, another part of the limbic system, is involved in forming, organizing, and storing memories. It’s also involved in connecting sensations and emotions to these memories, which is why a particular smell or song can often trigger a specific memory.
The Thalamus and the Hypothalamus
The second major structure of the forebrain, the thalamus, is basically the brain’s switchboard or air traffic control system. It takes in information from various sensory systems throughout the body and then directs that information to the appropriate part of the brain.
Directly underneath the thalamus is the hypothalamus, which controls temperature as well as many basic motives and drives: hunger, thirst, sex, aggression.
Many people find it hard to maintain weight loss over long-term and one explanation is that eating a diet high in fat and sugar for years can damage the hypothalamus. So, people continue to feel hungry, and eat, even when their body absolutely doesn’t need those extra calories, making it really hard to lose weight.
The Cerebral Cortex
The thin surface layer of the brain is called the cerebral cortex and it controls the most complex behaviors and higher mental processes: recognizing a friend, reading a book, playing games. The cerebral cortex is very thin, about one-eighth of an inch thick, but its numerous wrinkles create a much larger surface area.
Just below the cerebral cortex, the brain is divided lengthwise into two cerebral hemispheres, which together amount to about 80% of the brain’s total weight.
The Cerebral Hemispheres
The two cerebral hemispheres are made up of about 30 billion neurons and nine times as many glial cells, which provide support and protection for the neurons.
The two hemispheres of the forebrain control opposite sides of the body—the right hemisphere controls the left-hand side of the body and vice versa. These two hemispheres are connected by the corpus callosum, a large bundle of more than 200 million nerve fibers located just above the thalamus, which sends information back and forth between the two sides.
However, contrary to some popular accounts, the two hemispheres do work together in a coordinated and integrated way; you don’t use just one side of your brain at a time. Instead, the two sides tend to work together on related aspects of a task. For example, the left hemisphere might process the specific words you are hearing in a conversation, while the right hemisphere would help you understand the tone and context of the words.
Common Questions about the Brain’s Parts and Their Functions
The hindbrain consists of three separate parts: the medulla, the pons, and the cerebellum.
The four key structures of the forebrain are the limbic system, the thalamus, the hypothalamus, and the cerebral cortex.
The two cerebral hemispheres are connected by the corpus callosum, a large bundle of more than 200 million nerve fibers located just above the thalamus, which sends information back and forth between the two sides.
