Lecture 23: Language & Brain I

Some interesting links for this week:

"The brain reads sound by sound" (from the Baltimore Sun)

Dyslexia, Scientific American article by Sally Shaywitz of Yale University Medical School

The story of Phineas Gage (from Discover magazine)

Functional Neuroanatomy (a quick overview with excellent illustrations from the Univ. of Texas, San Antonio)

Neuroscience for Kids homepage (very nice site -- brain science for the rest of us)

Outline

• Bird brains
• Left-brain, right-brain
• Aphasia: disorders of language due to brain-damage

(how careful linguistic analysis has led to better understanding of language disorders)

Related, but different, questions about human brain and language

1. Clinical

• What will a person be unable to do if he/she suffers brain damage affecting language
• What are the chances of recovery? (Is this affected by age, gender etc.?)
• If part of the brain needs to be surgically removed (e.g., in order to control severe epilepsy, or to remove a brain tumor), which parts of the brain must be spared for language to be preserved?

2. Scientific

• Why do specific types of damage cause specific problems?
• What can this teach us about how the human mind is organized?
• What can this teach us about the organization of human language?

Comparison with Birdsong (again)

Song Sparrow

critical period; interaction of nature (innate abilities) with environment (input)

Special properties of song due to special properties of Song Sparrow's brain

Brains of Songbirds

Song areas very well defined

Specific functions understood

Known how they develop

Understood down to level of single neurons

Brains of Humans

Situation with humans is less clear

Some understanding of critical brain structures

a good deal of interesting clues to what the function of these structures is

Many things very unclear

Little known about development of language in the brain

...part of the problem is in our level of understanding of human language

Outline of human brain

Cortex

evolutionarily later

supports "higher" brain functions, including language

thin, folded sheet on surface of brain

Hemispheres

2 sides of brain: roughly symmetrical

Lobes and smaller areas of brain

frontal, temporal, parietal, occipital

Microstructures: neurons, networks

~10 billion neurons in human brain

Left-brain, Right-brain

• Left-hemisphere dominance for language
• Language damage far more likely following left-hemisphere damage
• Not so true in left-handers (around 50% show switched dominance)
• Not true in children
  • severe left-hemisphere damage (or loss) early in life: recovery very likely
  • therefore: Left Hemisphere specialization isn't fixed at birth ... emerges in development
• Not entirely clear in females
  • LH damage: better chance for recovery of language functions than males
  • Recent fMRI evidence suggests that some but not all language functions may be less lateralized to the left hemisphere in females
  • However, this evidence -- while intriguing -- does not justify exaggerated conclusions drawn in the popular media. It most definitely does not lead to the conclusion that "men and women think differently", at least in the way that this common prejudice is generally thought of.

 

Activation in female brains when performing phonological task (rhyming judgment); work by Shaywitz & Shaywitz and colleagues at Yale Medical School.

Broca's Aphasia

• Identified 1861 by Paul Broca, a Parisian neurologist
• Patient "Tan": intelligent, good language comprehension, severe deficit in speech production
• Died soon afterwards: brain showed selective damage at junction of frontal, parietal, tempral lobes, left hemisphere

Typical clinical symptoms of Broca's aphasics

"Yes ... Monday ... Dad, and Dad ... hospital, and ... Wednesday, Wednesday, nine o'clock and ... Thursday, ten o'clock ... doctors, two, two ... doctors and ... teeth, yah. And a doctor ... girl, and gums, and I."

 

"Me ... build-ing ... chairs, no, no cab-in-ets. One, saw ... then, cutting wood ... working ..."

Wernicke's Aphasia

• Identified 1873 by Carl Wernicke, eminent German neurologist
• Patient with reasonably good speech, very poor language comprehension
• Died soon afterwards: brain showed selective damage in rear parietal/temporal region, left hemisphere

Typical symptoms of Wernicke's aphasics

Examiner: What kind of work have you done?

Patient: We, the kids, all of us, and I, we were working for a long time in the ... you know ... it's the kind of space, I mean place rear to the spedawn ...

Examiner: Excuse me, but I wanted to know what work you have been doing.

Patient: If you had said that, we had said that, poomer, near the fortunate, porpunate, tamppoo, all around the fourth of martz. Oh, I get all confused.

Classical Understanding of Language in the Brain, based on Aphasias

Broca's Area: responsible for speech production (close to motor areas)

Wernicke's Area: responsible for speech comprehension (close to auditory areas)

Striking confirmation: Conduction Aphasia

• often associated with damage to Arcuate Fasciculus -- a tract of fiberts connecting BA and WA
• patients reported to show good comprehension, good production, poor repetition

Revised Understanding of Aphasia (to be discussed on 12/9)

Wernicke's patients clearly don't have just a comprehension problem

a. speech is typically somewhat incoherent

 

b. patients perform very poorly on semantic judgments

 

dog cat turnip

man woman trout

--> deficit may be in semantic component of language

Broca's patients turn out to have a comprehension problem, when carefully tested

a. passive sentences

 

i. The dog chased the cat

ii. The girl threw the ball

 

iii. The cat was chased by the dog

iv. The ball was thrown by the girl

 

--> using word-order 'strategies' rather than syntax

 

b. attention to determiners

 

i. He showed her baby pictures

 

ii. He showed her the baby pictures

iii. He showed her baby the pictures

--> deficit may be in syntactic component of language