Where we are on the pyramid

Neuroscience

• Neuroscience: The biological study of the brain and nervous system.
  • Ex: how neurons fire, which brain regions activate during different tasks, the physical effects of brain damage
• Cognitive psychology studies mental processes (the software); neuroscience studies the physical brain (the hardware) where we look for evidence of those processes.
• However, given the brain’s importance to all mental processes, we need to understand some neuroscience basics.

Three kinds of evidence, and one tool

1. Damage. Something destroys part of a brain. See what stops working.
2. Disconnection. Surgery separates the two halves. See what changes.
3. Intervention. A researcher changes a brain on purpose. See what follows.

All three work the same way. A brain is altered, and we watch what the person can no longer do. They differ in who does the altering and how much say the researcher has in it.

Phineas Gage, 1848

• An explosion drove an iron rod through the front of Phineas Gage’s brain, on the left side. He survived and was observed for years afterward.
  • His physician reported that his personality changed, while his memory, movement, and speech did not.
• This was the first case to suggest that specific brain regions control aspects of personality.

H.M., 1953

• Surgeons removed parts of H.M.’s brain to treat severe epilepsy. He survived and was studied for over 50 years.
  • Researchers found that he lost the ability to form new long-term memories, while his personality, intelligence, and older childhood memories remained intact.
• This was the first case to show that specific brain regions control specific types of memory.

What damage cases establish: Localization

• What do damage cases tell us?
• Localization: The principle that different regions of the brain specialize in different functions.
  • Ex: Damage at the back of the brain can leave someone unable to see, with working eyes.
  • Ex: Damage to one small region on the left can take away fluent speech and leave comprehension intact.
  • Ex: Damage to another small region can leave someone unable to recognize their own family by face, while still recognizing them by voice.
• NOTE: Damage can show that a brain region is necessary to do, think, or feel a particular thing. It does not show that the region is sufficient to do, think, or feel that particular thing on its own. Many things require multiple brain regions.

Evidence Type 2: Disconnection

• The reasoning: if the halves are separated and information given to one half never reaches the other, then whatever only one half can do belongs to that half alone.
• The brain is divided down the middle into a left and a right half, each called a hemisphere. A thick bundle of nerve fibers runs between them and carries signals from one to the other.
• Researchers cannot cut that bundle for an experiment, so these studies use patients whose bundle was cut to treat severe epilepsy.

Sperry and Gazzaniga, 1960s

• Surgeons severed the corpus callosum (the bridge connecting the left and right hemispheres of the brain) in patients with severe, uncontrollable epilepsy. Researchers ran experiments with these patients and found that the left and right sides of the brain functioned independently and processed information differently.
• These were the first cases to show that the two halves of the brain do different jobs, and that only one of them produces speech.

The split-brain experiments

What split-brain cases establish: Lateralization

• Lateralization: The principle that the two hemispheres (halves) of the brain differ in function, with each one controlling the opposite side of the body.
• In experiments, a split-brain patient could pick up an object with their left hand (controlled by the right half of the brain), yet simultaneously claim they didn’t know what it was because the left side’s speech center never received the visual signal.
• NOTE: Lateralization refers to which hemisphere carries out a specific function. It has nothing to do with the popular claim that a person is “left-brained” or “right-brained”.

Evidence Type 3: Intervention

• An intervention is a change the researcher makes on purpose, before measuring what follows from it.
• Damage and disconnection wait for something to happen to a patient. Here the researcher decides what changes, who it happens to, and when.
• The reasoning: if changing a region changes what a person can do, that region was doing the work, rather than sitting nearby while the work happened somewhere else.
• That control is what makes this the strongest of the three.

Two ways to change a brain on purpose

• Interrupt it. A magnetic pulse delivered from outside the skull briefly stops one region from working. Performance on a task is measured during the pulse and again after it.
• Train it. Measure an ability. Have people practice it for months. Then measure the brain again and see what changed.

Cohen and colleagues, 1997

• In people blind since early childhood, the region that normally handles vision responds while they read Braille with their fingers. Researchers interrupted that region with magnetic pulses while blind adults read Braille, and interrupted the same region in sighted adults doing a comparable task with their fingers.
  • The blind participants made errors. The sighted participants were unaffected.
  • The part of the blind participants’ brains that normally processed vision had adapted to instead process touch for them, so when this area was interrupted, their ability to do the task was impacted. For sighted people, the interruption did nothing to their ability to process touch b/c their brains don’t use that region for touch. ## What intervention establishes: Neuroplasticity {.sm}
• Neuroplasticity: The principle that the brain changes its structure and function in response to experience or injury.
  • Ex: People blind from early childhood use the region that normally handles vision to process touch and sound instead.
  • Ex: A musician’s brain differs measurably from a non-musician’s in the regions controlling the trained hand.
• The brain gets less plastic as we age, though!