In 1848 a railroad construction foreman in Vermont named Phineas Gage survived an accident that drove an iron rod up through his cheek and out the top of his head, badly damaging his frontal lobe. His doctor, John Harlow, later reported that his personality changed so much his friends said he was no longer the same man. Gage became one of the most famous cases in psychology. As we'll see, the story you usually hear is simpler than the evidence.
The four lobes
The cerebral cortex is the brain's wrinkled outer layer. Each hemisphere is divided into four lobes.
- Frontal lobe: planning, decision-making, self-control and voluntary movement. The motor cortex sits at its back edge, and Broca's area (usually on the left) helps produce speech.
- Parietal lobe: touch and body position, through the somatosensory cortex, plus spatial awareness.
- Temporal lobe: hearing, and roles in understanding language (Wernicke's area, usually on the left) and memory.
- Occipital lobe: vision.
Each hemisphere mainly controls the opposite side of the body. That's contralateral control.
Below the cortex
- The brainstem keeps you alive. The medulla controls heartbeat and breathing, the pons relays signals, and the reticular formation helps keep you alert.
- The cerebellum coordinates movement and balance and helps you learn skills like riding a bike.
- The thalamus relays most sensory signals to the cortex. Smell is the main exception.
- The hypothalamus helps regulate hunger, thirst and body temperature, and controls the pituitary gland.
- The amygdala is involved in emotion, especially detecting threats.
- The hippocampus is crucial for forming new memories of facts and events.
The amygdala, hippocampus and hypothalamus are often grouped as the limbic system, a loose label for structures linked to emotion and memory.
Regions work in networks
A brain map can make it look as if each region does one job. It's more accurate to say a region is involved in a function. Recalling a memory, reading a sentence or feeling afraid draws on many regions working together, and one region takes part in many tasks. Calling the amygdala "the fear center" is a shortcut, not a description.
The case of H.M.
In 1953 a surgeon removed large parts of the medial temporal lobe on both sides of Henry Molaison's brain, including much of the hippocampus, to treat severe epilepsy. Afterward he could hardly form new memories of facts and events. Psychologist Brenda Milner found he could still get better at a mirror-drawing task over several days, while not remembering having practiced. His case showed that different kinds of memory depend on different brain systems.
The corpus callosum and split brains
The corpus callosum connects the two hemispheres. Some patients with severe epilepsy had it cut. Roger Sperry and Michael Gazzaniga showed that when information reached only one hemisphere, these patients sometimes couldn't name what they had seen, yet could pick it out by touch. Sperry shared the 1981 Nobel Prize in Physiology or Medicine for this work.
Myths, then the fix
- "We only use 10% of our brains." Brain scans show activity across virtually every region over a normal day, and damage to almost any area causes some problem.
- "Left-brained and right-brained people." Some functions lean to one side; language relies mostly on the left hemisphere in most people. But a 2013 University of Utah study of brain scans from more than 1,000 people found no sign that people are left-brained or right-brained overall.
Where the research is shaky
Gage's case is often told as a man turning permanently cruel and unstable. Historian Malcolm Macmillan found evidence that Gage later worked for years as a stagecoach driver in Chile, which suggests he recovered a good deal. Exactly how much he changed, and for how long, is still debated.
Common mix-ups
- Thalamus vs hypothalamus. The thalamus relays senses; the hypothalamus regulates body states.
- Broca's vs Wernicke's. Broca's is mainly producing speech; Wernicke's is mainly understanding it.
- Cerebellum vs cerebrum. The cerebellum is the small structure at the back that coordinates movement.
Frequently asked questions
What are the main parts of the brain and their functions?
The cerebrum's four lobes handle planning, touch, hearing and vision; the brainstem runs life support; the cerebellum coordinates movement; and limbic structures support emotion and memory.
Do we really only use 10% of our brain?
No. Brain scans show activity in virtually every region, and damage to almost any area causes some loss of function.
Are people left-brained or right-brained?
No. Some functions lean to one hemisphere, but a large brain-scan study found no evidence that whole people are dominated by one side.
Which part of the brain controls memory?
No single part. The hippocampus is crucial for forming new memories of facts and events, but memory relies on networks across the brain.
Try it
Pat your head and rub your stomach at the same time, then switch hands. Notice how hard it is at first and how quickly it improves. Your cerebellum and motor cortex are learning together.