Linguistic brain

What is language

→ verbal message and some of the paraverbal components

2 properties common to every language

• decomposable

• Combinable

What is communication

• everything that conveys a message

• 93% of communication is non-verbal. Only 7% of the message is conveyed by language

• Irony, mood, emotions …

3 theories of origin of language

• gestural theory = upper limbs were free for some social communication

• Vocal theory = from vocalising natural sounds/cries to speech

• Mixed theory = this explains the dominance of the left hemisphere in verbal and sign language, started with gestures, then shaped speech

Mirror neurons role in origin of language

• Bridge between action observation and action production

• Suggests language came from them firing when seeing and reproducing speech

• Wider than other species

How do mirror neurons contribute to language

1. Prepare for the action

2. Internal representation

3. Neural basis of understanding others actions

Area is wider than other species

Motor theory of linguistic perception

• the listener understand the speaker because the articulatory gestures mirror neurons are activated

• Not a sound based perception of language, but a motor one

• Brain scans activated more for movements that words

Components of language and comprehension

Phonetic = physical acoustic properties

Phonology = systemic organisation of letters

Lexicon semantics = conceptual representations of meanings

Morphology = each letter

Syntaxis = grammatical rules of that language

Pragmatic = how context contributes to meaning

Wernicke’s model 1874

included Broca’s area (language production), Wernicke’s area (language comprehension) and connections between them

Lichtheim and Wernicke 1885

• balance between localisation views and connectionism

• Has to be somewhere in the brain responsible for elaboration etc

Later developed more by Geschwind 1965

Where are Broca’s and Wernicke’s areas

Broca’s = left frontal lobe

• posterior inferior frontal gyrus

Wernicke’s = left temporal lobe

• posterior superior temporal lobe

Broca and Wernicke’s functions

Broca = speech production

• motor moveemtns

Wernicke’s = comprehension

• processing and understanding

When is language lateralised

• bilateral involvement when learning a new language

• Left dominance is then established

non-verbal communication brain area

Non-dominant hemisphere - right

Homologus areas and bilateral PFC

What is the role of the arcuate faciculus

White matter tracts → to connect Broca’s and Wernicke’s

• Mainly recruited for non-semantic words (filler words)

Comprehension

→ detecting + decoding

• detected frequency range = 20-20,000 Hz

• Modulated by attention

Dual-stream model Hickok and Poeppel2007

• proposes a ventral stream processes speech recognition

• A dorsal stream translates acoustic speech signals into articulatory representations (speech production)

• Ventral = temporal lobe, lexical interface

• Dorsal = posterior frontal and posterior temporal

Ventral stream - parallel analysis

Two pathways go from the acoustic input to the lexical phonological network:

1. Gamma range = fast

• Suitable for segment-level info

2. Theta range = slow

• Syllable level info

What is the dorsal stream in language

• learning to speak is a motor learning task

• Primary input when learning is sensory

• must be a neural mechanism that encodes and maintains speech sounds

• Altered auditory feedback disrupts speech production

Imaging evidence for a sensorimotor dorsal stream

• recent imaging has identified neural circuit that supports auditory-motor interaction

• Includes the posterior STS, a left Sylvian fissure and left posterior frontal regions

Where is the neural activation of phonetic/phonology/lexicon

• phonetic = dorsal STG

• Phonology = mid/posterior STS

• Lexicon-semantic = ITS, MTG

• Morphology and syntaxis - distributed

What is aphasia

→ impaired language or communication caused by a damage or injury at some level on the neural pathways of L&C - stroke

• different types - Broca’s aphasia and Wernicke’s

• Main distinction = expressive vs comprehension

Impairments in expression vs comprehension

Language impairments:

• difficulty finding words

• Grammatical errors

• Fluent speaking issues

Comprehension impairments:

• difficulty understanding

• Providing unrelated answers

• Hard to follow TV/fast speech

Fluent vs non-fluent aphasia

Fluent = able to produce connected speech, but lacks meaning

Non-fluent = speech is halting and effortful, grammar is impaired

Brocas aphasia

• inferior frontal gyrus (brocas area)

• Speech production affected

• Non fluent, poor repetition

• Comprehension intact

Werncikes aphasia

• STS, STG

• Comprehension impaired

• Fluent

• poor repetition

Other types of aphasia

• PPA → primary progressive aphasia, subtype of temporal dementia

• Crossed aphasia → damage to dominant side of body

• Subcortical aphasia → damage to subcortical regions

Brain imaging temporal and spatial resolution

• fMRI or PET - good spatially but poor temporally

• EEG and MEG accurately record the electrical activity of the brain at the millisecond time scale

What are event related potentials

• measured brain responses from EEG, triggered by events/tasks

What is mismatch negativity

Perceiving an element of novelty

Mismatch response

• neural activity supressed for expected stimuli, and enhanced for novel stimuli

• Reduced MMR amplitude is a clear marker for dysfucntion