NEUROLINGUISTICSCompiled by Dr PS Deb

NEUROLINGUISTICS

Neurolinguistics is the study of the neural mechanisms in the human brain that control the comprehension, production, and acquisition of language.

Harry Whitaker, who founded the Journal of Neurolinguistics in 1985

PET, fMRI, EEG, MEG help to find the language related brain activity in normal individual

An interdisciplinary field, such as neuroscience, linguistics, cognitive science, neurobiology, communication disorders, neuropsychology, and computer science.

Subfield DescriptionResearch questions in

neurolinguistics

Phonetics the study of speech sounds

how the brain extracts speech sounds from an acoustic signal, how the brain separates speech sounds from background noise

Phonologythe study of how sounds are organized in a language

how the phonological system of a particular language is represented in the brain

Morphology and lexicology

the study of how words are structured and stored in the mental lexicon

how the brain stores and accesses words that a person knows

Syntaxthe study of how multiple-word utterances are constructed

how the brain combines words into constituents and sentences; how structural and semantic information is used in understanding sentencesSemantics

the study of how meaning is encoded in language

LOCALIZATIONS OF LANGUAGE PROCESSES (AREOLOGY)

Investigated the locations of specific language "modules" within the brain. What course language information follows through the brain as it is processed. Whether or not particular areas specialize in processing particular sorts of

information. How different brain regions interact with one another in language processing. How the locations of brain activation differs when a subject is producing or

perceiving a language other than his or her first language.

TIME COURSE OF LANGUAGE PROCESSES The use

of electrophysiological techniques to analyze the rapid processing of language in time.

The temporal ordering of specific peaks in brain activity may reflect discrete computational processes that the brain undergoes during language processing.

E.g. one neurolinguistic theory of sentence parsing proposes that three brain responses (the ELAN, N400, and P600) are products of three different steps in syntactic and semantic processing

LANGUAGE ACQUISITION The relationship between

brain structures and language acquisition

Infants from all linguistic environments go through similar and predictable stages (such as babbling),

To find correlations between stages of language development and stages of brain development. 

The physical changes (known as neuroplasticity) that the brain undergoes during second language acquisition, when adults learn a new language.

NEUROLINGUISTICS METHODS

Lesion studies Neuroanatomy Stimulation studies Neuroimaging Electrophysiology Psycholiguistics Language Pathology

EXPERIMENTAL PARADIGMS

Mismatch paradigm Violation-based Priming Stimulation Subject tasks Lexical decision Grammaticality judgment, acceptability

judgment Probe verification Truth-value judgment Active distraction and double-task

HISTROY

Willium Wunddt: Founder of experimental psychology. Language as mechanism to transform thought into sentence

Gall: Phrenology Broca : First case of

expressive aphasia Wernikes: First case of

comprehension aphasia

LANGUAGE AREA IN PHRENOLOGY

BROCA’S APHASIA

Autopsy of a patient who could understand, with normal speech apparatus but could not speak or write a sentence.

Only articulate sound he could make was “tan”

After autopsying eight similar patient with lesion in the left frontal lobe

He made a famous statement that “we speak with the left hemisphere”1. language articulation lies the third frontal convolution of the inferior frontal gyrus; 2. there is left hemisphere dominance in language articulation;3. understanding language is a different cognitive task than producing it.

Paul Broca 1861

WERNICKE’S APHASIA

Ten years later, Carl Wernicke, a German neurologist,

discovered another part of the brain, this one involved in

understanding language, in the posterior portion of the left

temporal lobe.

People who had a lesion at this location could speak, but

their speech was often incoherent and made no sense.

Carl Wernicke 1871

The Aphasic Symptom complex (1874)

language processing is distributed in the brain, which is the central idea of most current cognitive models. He also made the correct prediction that patients with damage in the arcuate fasciculus would not be able to repeat speech sounds, a dysfunction later named as Conduction aphasia.

Wernicke’sBroca’s

LICHTHEIM’S HOUSE MODEL 1885WERNICKE-LICHTHEIM’S CONNECTIONISM

B

A M

THE WERNICKE-GESCHWIND MODEL OF LANGUAGE

B

A M V

HANDEDNESS AND LANGUAGE

THE BRAIN’S ANATOMICAL ASYMMETRY

LATERALIZATION OF LANGUAGE: WADA TEST

SPIT BRAIN EXPERIMENT

CHALLENGING CLASSICAL MODEL

BF Skiner: Behaviourist – Verbal behaviour 1957, Learning of language can be seen as mechanism

of reinforcement Noem Chomsky 1957 Syntactic structure

Ability to invent language is coded in gene and basis of understanding is similar across culture

There might be universal grammar Language is more widely represented than

older model Role of Motor cortex in comprehension Role of Right hemisphere more than realized

CORTICAL MAPPING OF THE LANGUAGE AREAS IN THE LEFT CEREBRAL CORTEX DURING NEUROSURGERY

(A) Location of the classical language areas.

(B) Evidence for the variability of language representation among individuals.

The number in each circle indicates the percentage of the patients who showed interference with language in response to stimulation at that site.

Note also that many of the sites that elicited interference fall outside the classic language areas. (B after Ojemann et al., 1989.)

LANGUAGE RELATED AREA OF LEFT BRAIN PET

GESCHWIND’S TERRITORY

the inferior parietal lobule is connected by large bundles of nerve fibres to both Broca’s area and Wernicke’s area.

Information might therefore travel between these last two areas either directly, via the arcuate fasciculus, or by a second, parallel route that passes through the inferior parietal lobule.

The inferior parietal lobule is one of the last structures of the human brain to have developed in the course of evolution

AREA 24: INITIATION AND MAINTENANCE OF SPEECH

They are also important to attention and emotion and thus can influence many

higher functions. Damage to these areas does not cause an aphasia in the proper sense but impairs the initiation of movement (akinesia) and causes mutism, the complete absence of speech. Mutism is a rarity in aphasic patients and is seen only during the very early stages of the condition. Patients with akinesia and mutism fail to communicate by words, gestures, or facial expression. They have an impairment of the drive to communicate, rather than aphasia.

LANGUAGE-RELATED AREAS IN THE HUMAN BRAIN.

The implementation system is made up of several regions located around the left sylvian fissure. It includes the classical language areas (B = Broca's area; W = Wernicke's area) and the adjoining supramarginal gyrus (Sm), angular gyrus (AG), auditory cortex (A), motor cortex (M), and somatosensory cortex (Ss). The posterior and anterior components of the implementation system, respectively Wernicke's area and Broca's area, are interconnected by the arcuate fasciculusThe mediational system surrounds the implementation system like a belt (blue areas). The regions identified so far are located in the left temporal pole (TP), left inferotemporal cortex (It), and left prefrontal cortex (Pf). The left basal ganglia complex (not pictured) is an integral part of the language implementation system

THE BRAIN CORRELATES OF A GIVEN COGNITIVE REPRESENTATIONRepresentation R and process P implies answers to (at least) four critical

questions:

1. Where-question: Which brain parts, areas, and, eventually, neurons are

active during, and are critical for, process P and the representation(s) R P

relies on?

2. When-question: At which point in time in the usage or understanding of

language does process P occur; when is representation R activated and

processed?

3. How-question: Which neuronal circuit, which nerve cells linked in which

way, is the brain basis for representation R; which spatiotemporal pattern

of neuronal activation in this circuit does underpin the process P?

4. Why-question: For what reason are R and P located in these specific brain

parts and activated at these specific points in time, and why is R laid down

in this specific neuronal circuit, P being expressed by these specific

activation patterns?

SEARCH FOR MEANING CENTERS?

PET SPEAKING TASK (NAMING)

BRAIN ACTIVATION PATTERNS DURING PASSIVE WORD READING

SCHEMATIC ILLUSTRATION OF THE CORTICAL SYSTEMS FOR LANGUAGE AND ACTION

PHONOLOGICAL PROCESSING OF SPEECH SOUND

The phonemes [p] and [t] for example were mapped to adjacent areas in superiortemporal gyrus, anterior to primary auditory cortex and Heschl’s gyrus.

A similar phonological mapping was evident in the motor system, where the production of [p] and [t] activated different precentral areas in a soma-totopic fashion.

The articulatory mapping of phonemes to the motor system corresponded to the localization of the articulators mainly involved in the production of the respective speech sounds — the lips for [p] and the tongue for [t]

SYNTACTICAL PROCESSING

When comparing grammatical sentences to word strings with syntactic errors, the latter elicit stronger brain activation in left perisylvian cortex, especially in inferior-frontal and in superior-temporal cortex

When directly comparing sentences with different grammatical structure, for example active and passive, subject and object relative, and coordinated and subordinated sentences, the grammatically more demanding sentences tended to elicit stronger activation; again some of the activation differences were located in left perisylvian cortex

SYNTACTIC NETWORKS IN THE HUMAN BRAIN

The frontal operculum and BA 44 together with the anterior STG, dealing with the structure of phrases (noun phrase, prepositional phrase etc.) and

BA 44/45, together with the posterior STG, being responsible for thematic role assignment

Within the latter network, BA 44 seems to process hierarchical structures independent of semantics (i.e. in natural and semantic-free artificial grammars [44,45]), whereas

The posterior STG seems to support the integration of syntactic and semantic information to achieve understanding (that is to understand who is doing what to whom).

THE RAPID TIME COURSE OF LANGUAGE UNDERSTANDING Language understanding is a relatively late

process Semantic processing, along with lexical ones, were

assumed to be first indexed by the N400 component of the event-related brain potential and field.

Syntactic processing was assumed to be indexed by an even later component, called P600.

Early near-simultaneous brain responses (latency <250 ms) index different facets of the comprehension process, including word form analysis, semantic access along with syntactic and semantic context integration, suggesting near-simultaneity (or short-delay seriality) in psycholinguistic information access.

The short delays are potentially accountable in terms of cortical conduction times

BRAIN-BASED MODELS OF CIRCUITS, THEIR ACTIVATIONS AND DELAYS

The areas shown on the brain diagram at the top and implemented in the model of the language cortex (MLC) at the bottom are:

Primary auditory cortex (A1), auditory belt (AB), auditory parabelt (PB), inferior prefrontal (PF), premotor (PM) and primary motor (M1) cortex. AB and PB together are sometimes called the ‘auditory language area’ or ‘Wernicke’s region’ and AB and PB the ‘motor language area’ or ‘Broca’s region’.

PROPOSED NEW MODEL - The ventral stream helps in

auditory “what” processing The dorsal auditory stream is

critical for auditory–motor integration

Early cortical stages of speech perception involve auditory-responsive fields in the superior temporal gyrus (STG) bilaterally.

This cortical processing system then diverges into two processing streams, a ventral stream, which is involved in mapping sound onto meaning, and

A dorsal stream, which is involved in mapping sound onto articulatory-based representations.

OF THE RELATION BETWEEN SYSTEMS SUPPORTING SUB-LEXICAL SEGMENTATION ABILITY AND AUDITORY COMPREHENSION ABILITY

Observed dissociations between these abilities arise when damage or functional imaging studies affect portions of the system after the divergence point, whereas we would predict some degree of correlation between these abilities if damage or functional imaging targets earlier shared components of the system.

G. Hickok, D. Poeppel / Cognition 92 (2004) 67–99 77

THE DUAL-STREAM MODEL OF THE FUNCTIONAL ANATOMY OF LANGUAGE

Hickok, Gregory & David Poeppel. 2007. The cortical organization of speech processing.Nature Reviews Neuroscience 8, 393–402.

FROM BRAIN MECHANISMS TO EXPLANATION

The cortex is not, a tabula rasa learning structure. It is equipped with the structure and microstructure of areas, connections between areas and even the microstructure of neurons and their biochemical properties.

Fiber tracts in human and non-human primates

WHAT IS GAINED FROM RECENT NEUROSCIENCE RESEARCH? At the semantic level, language is

‘woven into action’ Motor and sensory systems activation

demonstrates semantic categories along brain dimensions

In the vicinity of sensorimotor domains, may play a role in abstract semantic processing and in general meaning access.

RECENT RESEARCH CONT…

Phonetic distinctive features have their correlates in local cortical activation in the auditory and motor systems

Neuronal ensemble theory along with empirical neurophysiological evidence supports the existence of discrete cortical representations and mechanistic underpinnings for rules of grammar.

It takes about half a second to understand a word or sentence — counted from the point in time when the last word critical for sentence understanding is first unambiguously present in the input — might imply a substantial delay in the comprehension process

RECENT RESEARCH CONT…

Supportive of rapid, almost instantaneous understanding comes from recent neurophysiological studies suggesting latencies of <250 ms of the earliest brain correlates of semantic word and sentence understanding and syntactic parsing.

These neurophysiological results support rapid and parallel psycholinguistic models and argue against slow-serial or -cascaded theories assuming sequential steps from phonological to syntactic and semantic modules of hundreds of milliseconds

HEMISPHERIC FUNCTION FOR LANGUAGE

LANGUAGE AQUISITION

THE DEVELOPMENT OF LANGUAGE: A CRITICAL PERIOD IN HUMANS

 A critical period for learning language is shown by the decline in language ability (fluency) of non-native speakers of English as a function of their age upon arrival in the United States

FIBER TRACTS IN ADULTS AND CHILDREN

.Differences in fractional anisotropy between adults and 7-year-old children: (a) more medial and (b) more lateral sagital slices of the left hemisphere.

J. Brauer, PhD thesis, Leipzig University, 2008.

SIGN LANGUAGE

Signing deficits in congenitally deaf individuals who had learned sign language from birth and later suffered lesions of the language areas in the left hemisphereLeft hemisphere damage produced signing problems in these patients analogous to the aphasias seen after comparable lesions in hearing, speaking patients

BRAIN ACTIVATION IN CONGENITALLY BLIND SUBJECTS DURING A VERBAL-MEMORY TASK

IN PEOPLE BORN BLIND, BRAIN REGIONS THAT USUALLY PROCESS VISION CAN TACKLE LANGUAGE.

FUTURE

A neuro-mechanistic explanations detailing why specific brain areas are necessary for, or light up and index, specific facets of language processing,

how neuronal ensembles and distributed areas become activated with precisely timed milli-second delays, and which precise neuronal wirings can potentially account for neurometabolic activation of specific cortical clusters in semantic understanding

THANK YOU