Brain and Language

• If the human mind was simple enough to understand, we'd be too simple to understand it.  - Emerson Pugh (retired IBM scientist, author)

Some fun background

• Main Entry: sin·is·ter

Function: adjectiveEtymology: Middle English sinistre, from Latin sinistr-, sinister on the left side, unlucky, inauspicious

• Left side: associations?• Right side: associations? • http://www.bodymap.com/newsface.html

Crisscrossed (contralateral) Control

• “If I forget thee, O Jerusalem, let my right hand forget her cunning. If I do not remember thee, let my tongue cleave to the roof of my mouth” (Psalm 137:5-6)

Left hemisphere (language) – right side of body / perceptual space

Right hemisphere – left side of body / perceptual space

- everything is “crossed” except for smell!

Language on the Left

• Tapping experiments: – shadow speech and tap with each

syllable– easier to tap with left finger than with

right

• Dichotic listening:– play different words to each ear– hear linguistic input better with right

ear

More “Language on the Left”• Recognize words better when flashed to right

visual field than left – (even in RL languages)

• Differentiate linguistically significant sounds (tones/length) better with right ear– left ear better at discriminating music (for non-

musicians)

STAIR ● CHAIR

صورة ● كرسي

Surgical demonstrations

• Can temporarily paralyze one hemisphere (by injecting sodium amytal into the carotoid artery)

– Patients with sleeping RH can talk– Patients with sleeping LH cannot

• During brain surgery, small electric shocks to parts of the left hemisphere will silence patients mid-sentence

Hemiplegia and Hemispherectomies

• Hemiplegia: – Paralysis of one side of body due to brain lesions – In children, paralyzed right side predicts deficiency

in language acquisition

• Hemispherectomy: – Surgical removal of one side of the brain– Remove LH:

• lose most language, keep visual/spatial abilities

– Remove RH:• keep most language, deficiencies vary greatly

Early Hemispherectomies

• Dennis & Whitaker (1976)– 3 hemispherectomy patients (all younger than

5 mo.)– studied when 9 & 10 y.o.– LH removed – couldn’t distinguish between

grammaticality of sentences:• *I paid money by the nun• *I was paid money to the lady• I was paid money by the boy

Separating the two hemispheres

• Commisurotomy: severing the corpus callosum for severe, incurable epilepsy

• IQs tests: left hemisphere alone usually tests as intelligent as both hemispheres before the operation

• Left visual field: disconnected from language center

●

CLAP ● LAUGH(left half of their world has been disconnected

from their language center)

Right hemisphere and language• Word semantics (Beeman 1998)

– Processing relatedness of words, predicting meaning– Activates less-likely meanings of words weakly

• Understanding discourse, speaker’s intention– Interpreting narrative script, making inferences…

• Metaphor (Brownell 1988) – More blood flow to the right hemisphere when asked to

judge metaphor plausibility “The inventors were squirrels collecting nuts”

• Compensates for left hemisphere damage (esp. with children)– Smith and Sugar (1975) removed a boy’s left hemisphere at

5 years, 6 months. As an adult, normal language and intellectual capacities

Handedness and lateralization

• 90% of population: 1 or 2 copies of dominant gene causing strong Right-hand bias

• Lefties comprise about 9% of the worldwide population– 19%: language primarily in the right

hemisphere

• (The corpus callosum for left-handers and ambidextrous people is 11% larger)

Left Hemisphere

When do we lateralize?

• Lateralization not present at birth?– or is the brain just plastic?

• Children with brain damage before 2 y.o., damage to RH disrupts speech as much as damage to LH

• Children with brain damage between 2-10, more speech disturbance when LH damaged

The anatomy of the brain

4 lobes:• Frontal• Parietal• Occipital• Temporal

Sylvian Fissure: Separates the Frontal and Parietal lobes from the Temporal lobe

Major Language Areas:

Frontal Lobe

• Broca’s area – responsible for grammar?, inferior frontal gyrus of left hemisphere

• Motor area – on perimeter of the parietal lobe, specific regions dedicated to the motor abilities of specific body parts

• Supplementary motor area – programs motor sequences

• Prefrontal area – highest level of brain function, intellect, will, emotions – thought during speech

• Anterior Cingulate Gyrus – concentration (in the limbic system)

Motor Area

Temporal Lobe

• Primary Auditory Area – Contralateral, in the Sylvian fissure – Receives auditory information first

• Auditory Association Area– Superior temporal gyrus, (upper third of temporal lobe)– site of high-level functions that process information such as language

and music

• Wernicke’s Area– lesions make patients unable to understand speech (debatable claim)– Wernicke’s aphasics usually unaware that they have language difficulties

• Auditory Visual Association Area – posterior part of inferior temporal gyrus – lots of fiber communication with visual communication field – Involved in visual language processing and lip reading

Parietal and Occipital Lobes

Parietal Lobe: • Parietal Association Area

– communication fibers from all lobes densely connected– general somaesthetic sensing (feeling in arms, face, legs…)– visual and auditory senses also associated

Occipital Lobe:• Primary Visual Area

– very rear part of the brain (striate area around calcarine fissure) – visual information first enters this area and then is processed further by

visual association area• Visual Association Area

– around primary visual area, recognizes shape, color, movements

REVIEW

Is language due to brain size?

• No!

• The average human adult brain weighs about 3 lbs, which is nothing compared to an elephant’s brain

• Not due to high “brain mass: body mass” ratio– The brain mass : body mass ratio is the same for

• a 13-year-old boy• a 3-year-old chimpanzee

Is language in one area?• No…in fact, pinning down the area of the brain that’s

specialized for language is very difficult!

• Researchers thought they’d found the language center:– planum temporale (the horizontal part of the Sylvian Fissure)– Differences in the lengths of this region correspond to the development

of the different hemispheres– Deacon (1968) examined 100 human brains and found that 68 had

enlarged planum temporale on the left side, so determined that he’d found the “control center” for language

• also seems to be an area largely responsible for language processing and production, since this is where the auditory association cortex receives signals from the ear, which are processed and sent to other parts of the brain

– But Gannon and colleagues (1998) were examining chimp brains looking for asymmetries, and they found that 17 out of 18 chimp brains had enlarged plana temporale on left side!

• So chimps are more specialized for language than humans?