Linguistic brain

What is language

→ verbal message and some of the paraverbal components

2 properties common to every language

2 proprieties are 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 … are components that rely on inferential processes to be detected

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

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 production, acoustic properties

Phonology = systemic organisation of letters to create meaning

Lexicon semantics = meaning/content of words, synonyms/antonyms

Morphology = elaborates aspects of words like plurals

Syntaxis = grammatical rules

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 localisationist views and connectionism

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

• Good fro diagnosing speech deficits

• Mixture of auditory, motor and conceptual centres

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

Pragmatic/non-verbal 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

• dorsal pathway from language processing

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

Comprehension

→ detecting + decoding

• detected frequency range = 20-20,000 Hz

• Modulated by attention

• Role of para-verbal tracts in detection (type of sentence, someone we know etc.)

Dual-stream model Hickok and Poeppel2007

• proposes a ventral stream processes speech signals for comprehension

• A dorsal stream translates acoustic speech signals into articulatory representations

• Ventral = temporal lobe, lexical interface

• Dorsal = left dominant, frontal/parietal lobes, Sylvian area

Dual-stream - spectrotemporal analysis and phonological network

SA = analyses frequency and timing characteristics of sound

• superior temporal gyrus

PN = ‘sound based’ representations that can be mapped to meaning or motor actions

• superior temporal sulcus

Parallel analysis - ventral routes from acoustic input to lexical PN

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

1. Gamma range

• samples input in a fast rate

• Suitable for segment-level info

2. Theta range

• slower rate

• Syllable level info

What is the dorsal stream in language

• learning to speak is a motor learning task

• Primary input when learning is sensory, so 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 boundary between parietal and temporal lobes

Where is the neural activation of phonetic/phonology/lexicon

• phonetic = articulatory network

• Phonology = sensorimotor interface

• Lexicon-semantic = selection of target concept - distributedu

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 receptive

Impairments in expression vs comprehension

Language expression:

• difficulty finding words

• Grammatical errors

• Fluent speaking issues

Comprehension:

• difficulty understanding

• Providing unrelated answers

• Hard to follow TV etc

Fluent vs non-fluent aphasia

Fluent = speech production is halting and effortful, grammar is impaired

Non-fluent = can produce connected speech but it lacks meaning

Brocas aphasia

• inferior frontal gyrus (brocas area)

• Speech production affected

• Non fluent, poor repetition

• Comprehension intact

Werncikes aphasia

• superior temporal sulcus and gyrus

• Comprehension impaired

• Fluent but poor repetition

Other types of aphasia

• PPA → primary progressive aphasia, not actually aphasia, its a subtype of temporal dementia

• Crossed aphasia → person demonstrates language impairments after suffering damage to the hemisphere on the dominant side of the body

• Subcortical aphasia → damage to subcortical regions of the brain e.g. thalamus or basal ganglia, and symptoms can mirror those seen in cortical lesions

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

• This high temporal resolution allows exploration of other important aspects of brain reorganisation during aphasia recovery

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 is typically suppressed in response to expected stimuli and enhanced following novel stimuli

• This phenomenon is known as MMR

• autonomic brain response - a component of ERPs - triggered by unexpected ‘deviant’ stimuli in a sequence of regular, repetitive inputs

• Reduced MMN amplitude is a strong maker for dysfunction

• It is used in auditory and visual studies, with the somatosensory mismatch response being use to study tactile and age-related changes