Language in the brain

Language in the brain Linguistics lecture #7 November 16, 2006

Overview • Meet your brain! • Left brain, right brain • Are there “language organs”?

Parts of the brain

The cerebral cortex isn’t pudding

Why is it so wrinkled? • The cerebral cortex contains billions of neurons in layered neural networks • But it is only 1.5~5.0 mm thick! • Its area is about 830 cm2, too big to fit into your head unless it’s crumpled up

connection Two hemispheres

The wiring is “backwards” • Each hemisphere has direct contact mostly with the opposite side of the body!

Different talents • In general, the right hemisphere is better at processing wholes and spatial information • In general, the left hemisphere is better at analyzing into partsand time information

Which hemisphereis better at language? • Language involves analyzing parts related across time, right? • And in fact, most people process language more in the left hemisphere • But how do scientists know this? (They knew this long before the invention of machines and computers that could produce images of brain activity.)

Evidence from brain damage • “Loss” of language caused by brain damage is called aphasia • For 150 years, doctors have known that damage to the left hemisphere can cause aphasia, but damage to the right hemisphere mostly doesn’t

DOG CAT Experimental evidence • If language is processed better in the left hemisphere, which word should be easier to recognize? + DOG CAT • “CAT”, since its image goes directly to the left hemisphere

Split-brain evidence • To prevent epilepsy (癲癇) from affecting the whole brain, surgery can be done to cut the connection between the hemispheres

Testing split-brain patients • Show split-brain patients a picture on the left side • Results: They can choose the correct object with their left hand • But they can’t tell you the name of the object

Brain imaging • Today the “hottest” way to study language in the brain is to use special machines that can create images of brain activity EEG: measures electrical patterns on surface of brain (fast and cheap, but “blurry” pictures) PET: first inject radioactive stuff into the blood, make images of “glowing” blood flow (risky) fMRI: use magnets and quantum physics to make oxygen emit energy, then image blood flow (safe, pretty fast, pretty clear, but expensive)

Female Male Is your language in the left? • Brain imaging (and other evidence) shows that it depends on sex and handedness (women and lefties are less lefty) Phonological processing

Are there “language organs”? • Almost 150 years ago, French doctor Broca said he found one: Broca’s area • A little later, German doctor Wernicke said he found one too: Wernicke’s area • The modern view is that both areas are crucial to language, but have different jobs

Broca’s and Wernicke’s areas

Broca’s handles “grammar”? • Maybe, since damage there does this: Describe this picture: “Cookie jar ... fall over ... chair ... water ... empty.”

Well, this is... mother is away here working her work out of here to get her better, but when she's looking, the two boys looking in the other part. One their small tile into her time here. She's working another time because she's getting to. So two boys work together and one is sneaking around here making his work and his further funnas his time he had. Wernicke’s handles “meaning”? • Maybe, since damage there does this: Describe this picture:

then process grammar including phonology first process words and meaning A processing modelfor reading aloud

meaning everywhere phonology in left, but not all in Broca’s But brain imaging makes the picture more complex

The interactionists are happy! • “Every new functional imaging study seems to bring another language area to our attention.... This all leads to the conclusion that domains like language do not live within well-defined borders.…” Elman, Bates, Johnson, Karmiloff-Smith, Parisi, & Plunkett (1996). Rethinking innateness: A connectionist perspective on development. MIT Press.

The modularists are confused! • “But to be honest, no one really knows what either Broca's area or Wernicke's area is for.” Pinker (1994). The language instinct. William Morrow.

Summary • The brain’s “smartest part” is the cerebral cortex, divided into two hemispheres • The left hemisphere tends to be better at processing language, in general… • Evidence comes from aphasia, split-brain patients, experiments, and brain imaging • Broca’s area and Wernicke’s area have different functions • New evidence (especially from brain imaging) has made the notion of “language organs” less clear than it once was

Language in the brain