Nueral Structure of Language - 1.2

The brain is wrinkled

• maximize surface area because the outer layer of ur brain is very important 

The brain is divided into hemispheres

• Language distributed throughout brain , you need fiber pathways to connect them 

• Fiber pathway connecting 2 things - corpus callosum 

Brain hemispheres are divided into lobes

• Most of the processing looks the same - goes to one place no matter what mode of language 

  • Most language processed in temporal & frontal 

Brain divisions

Coronal - ear to ear 

Saggital - front to back 

axial - Horizontal

Brain positions

Inferior - bottom 

Anterior - front 

Superior - top 

Posterior - back 

ventricle - Further down

dorsal - Further up

Central Nervous system

•  86 billion neurons - 100 trillion nueral connections 

• Send and receive signals to neighboring neurons via electrical pulses 

• Typically connected to about 10,000 other neurons 

  • Massive degree of complexity 

How does the brain compensate for the brain being so slow to return to normal state after firing?

it has a huge number of neurons (tens of billions) and complicated connections between them.

Neurons dont exactly connect because

 gap between them because of terminal button - at end of neuron - send chemical messages to other cells

• contains synaptic vessels with neurotransmitters

What does terminal button do

• release chemical messages to communicate with cells in area

• An electrical impulse (action potential) travels down the axon and reaches the terminal button.

• Neurotransmitters release into the synaptic cleft (the tiny gap between cells).

• Receptor binding: Chemicals cross the gap and bind to receptor sites on the receiving cell (dendrite, muscle, or gland).

Cortex

• Outer layer 

• Higher level cognition 

• “Recently evolved” 

• Characterized by folds 

• Really shallow 

What space of the brain maximizes surface area the most?

cortex because of all of the folds

Korbinian Broadmann

• mapped different areas of brain - structurally grouped by similar cell types - bc organized in similar ways

Most language localized in

Left hemisphere

• curse words in right

“Left Hemisphere Dominance”:

• 95% for right-handers

• 70% for left-handers

Left vs right ear advantage

• you can understand something quicker on one side of you based on what side language is processed for you

Ex - left lateralized - quick to hear in right ear

right lateralized - quicker to hear in left ear

what does it mean that langauge localization is independent of modality

It means that no matter what type of language or what form the language is in

• spoken

• sign

it is all localized in same area - mostly left for people

• centralized modality network for lang everywhere

Subortical structure - basal ganglia

• voluntary motor movements, procedural learning, routine behaviors or

“Habits”…

Damage can cause movement disorders like Parkinson’s or Huntington’s or

neuropsychiatric disorders like Tourette’s, OCD, etc

• OCD - hyperactivity in Basal ganglia 

• Not just ab motor activities bur procedures in general

Motor movement and procedures can become automized by

•  shifting process from cortex to Basal Ganglia 

  • Ex: driving for first time vs regular, tying shoes 

Thalamus 

Relay site between sensory organs and cortex

Regulates sleep and wakefulness.

Defecit - Lesion Method process

Patient suffers stroke/accident, leading to brain damage. Patient’s behavior is studied.  Patient dies. Location of the damage is assessed in post-mortem analysis.  Hypotheses are developed about functional contribution of the damaged area based on the behavioral data collected while patient was alive.

How is lesion defect method used

• understand what is going wrong in brain - at algorithmic level

  • need description to know exactly

Can develop hypotheses of how that part of brain works 

• observe/do tests on person 

• Person will die so ater look at brain to see which part was affected 

Limitations of lesison defect method

• Slow

• Once the patient dies, no more data can be collected.

• Impossible to know who to test ahead of time.

  • Wait for ppl to get aphasia → test them → wait till they die 

  • post mortem - only way to know what acc happened/part of brain - didn’t have MRI, brain surgery

Broca’s aphasia

• Slow, laborious, non-fluent speech.

  • speech production affected

• Output limited to short utterances of less than four words.

• Comprehension relatively intact

•   Writing is limited.

Broca’s aphasia case study symptoms

• Prosity - contrastive focus in English 

• Emphasize words 

• Lots of hand gestures 

• Noun bias 

  • When asked about company says names first 

  • Nouns - dont require as much thought, tense, argument - subject object - like verbs do 

  • Children learn nouns 1st verbs second

• trouble/hesitation finding words - slow speech

• Thoughts intact - “brain good” 

  • understands what he wants to say

• Broadly distributed brain damage - affects movement - on left side - language production - right hand paralyzed when talking - left side controls right body 

• 1-3 words at a time 

• Something wrong with syntax/structure of sentences “I was, um seven years ago… she’s speech.” 

Aphasia

language deficits caused by brain damage

Wernicke’s aphasia

• Fluent but disordered speech. Similar writing.

• Impaired comprehension.

• Damage to the boundary of the temporal and parietal lobes.

Wernicke’s aphasia case study symptoms

• Opposite of Broca’s aphasia 

• Real deficit - comprehension

• Not aware they have aphasia 

  • Test ex maybe - do something non linguistic/commands 

• Fixed expressions intact 

  • Greetings 

  • High frequency sayings we use all the time processed as one word 

  • Prosody intact - sounds like convo if you zoom out 

    • Processed on right in ppl where language is processed on left 

• Repeats expressions 

• Understands when a question is being asked - personal and understanding of prosity still intact as well

Classical model of language processing

• states that specific brain functions are localized on left side of brain

Parts of classical model

Spoken word:

1. Primary auditory cortex

• Sound processed in 

2. Wernicke’s Area

• Comprehension of words 

3. Arcuate fasciculus

• connects broca’s and wernicke’s area - comprehension and production

• Other type of aphasia - conduction aphasia - perfectly comprehend and produce sentences clearly - can say gist of sentence but not repeat it verbatim

4. Broca’s Area

• Formulate response 

5. Primary motor cortex

• Send to BA6 - motor gestures of speech 

Criticisms of the classic model

Areas in model have other functions besides language 

• Broca’s area - not inherently motor related - musics and math too 

Other areas are involved in language processing as well.

Percentage of respondents endorsing particular definition of Broca’s area

• Basically we dont know exactly where it is/the boundaries 

• Author made up a whole definition and it was the most supported

• everyone has different understanding of area/defnintion

Sequence of words 

• Production of words 

    ↓                      ↑

Convert to representation 

• Comprehension of words 

Need some knowledge to do both

Syntactic constructions that Broca’s aphasics have trouble understanding

• comprehension not perfect

passives - The boy was chased ____ by the girl …

object relatives - The boy who the girl chased ____ …

object clefts -  It was the boy who the girl chased ____. 

Syntactic constructions that Broca’s aphasics understand ok

Actives - The girl chased the boy 

Subject relatives - The girl who___ chased the boy 

Subject clefts - It was the girl who____chased the boy

What does Broac’s area do?

Lesions in Broca’s area are not sufficient or necessary to induce syntactic deficits 

• Just because you have lesions in Broca’s area does not mean there will be syntactic deficits 

• Hard to localize & not perfect relationship 

• People get damage there & are fine, ppl have damage in other areas with effect 

maybe simple sentences easier to understand

to answer questions about underlying algorithms and functionality of Broca’s area

need to have clear algorithmic model