Physiology of Language

AREAS The primary brain areas concerned with language are arrayed along and near the sylvian fissure (lateral cerebral sulcus) of the categorical hemisphere. A region at the posterior end of the superior temporal gyrus called Wernicke’s area is concerned with comprehension of auditory and visual information. Broca’s area (area 44) in the frontal lobe.

Broca’s area processes the information received from Wernicke’s area into a detailed and coordinated pattern for vocalization and then projects the pattern via a speech articulation area in the to the motor cortex, which initiates the appropriate movements of the lips, tongue, and larynx to produce speech. The angular gyrus behind Wernicke’s area appears to process information from words that are read in such a way that they can be converted into the auditory forms of the words in Wernicke’s area.

Location of language areas

4 Processes in Speech Production Respiration Phonation Resonance Articulation

Respiration: Power Mechanism Provides the energy for sound Breathing results in:- a difference in air pressure is between the thoracic cavity and the atmospheric pressure outside the body

organs of respiration – trachea – rib cage – thorax – abdomen – diaphragm – lungs

HOW IT WORKS at rest, inhale and exhale with equal time thoracic cavity expands lungs expand, creating negative pressure and air now available for speaking to speak, lungs deflate and rib cage contracts forcing air out

Phonation: Vibrating Mechanism Phonation is the rapid opening and closing of the vocal folds for sound the vocal folds lie horizontally in the larynx They are attached anteriorly to the thyroid cartilage and posteriorly to the artynoid cartilages; they are free in the middle. the opening in the middle of the vocal folds is the GLOTTIS

• when airstream enters larynx, subglottic pressure builds up when pressure is great enough, vocal folds are pushed apart air flows through glottis reduction of pressure pulls vocal folds back together aerodynamic principle related to pressure changes called Bernouli effect

when vf are apart = abducted so opening is abduction when vf together = adducted during phonation, vf’s alternate between abduction and adduction

ARTICULATION articulation = joining together of speech organs for production of speech. Articulation is act of creating speech sounds The various articulators (Teeth, lips, tongue, jaw, etc.) alter the size, shape, and other characteristics of the resonant spaces in the vocal mechanism

Aphasias Aphasias are abnormalities of language functions that are not due to defects of vision or hearing or to motor paralysis. They are caused by lesions in the categorical hemisphere. Fluent, nonfluent, and anomic aphasias.

In nonfluent aphasia (EXPRESSIVE APHASIA, ANTERIOR APHASIA) the lesion is in Broca’s area Speech is slow, and words are hard to come by. Patients with severe damage to this area are limited to two or three words with which to express the whole range of meaning and emotion.

Fluent Aphasia ( RECEPTIVE APHASIA, POSTERIOR APHASIA) Lesion in the wernicke’s area Speech itself is normal and sometimes the patients talk excessively. However, what they makes little sense. The patient also fails to comprehend the meaning of spoken or written words.

conduction aphasia Lesion in the auditory cortex (areas 40, 41 &42) patients can speak relatively well and have good auditory comprehension but cannot put parts of words together or conjure up words. This is called conduction aphasia because it was thought to be due to lesions of the arcuate fasciculus connecting Wernicke’s and Broca’s areas.

Anomic aphasia When there is a lesion damaging the angular gyrus. There is trouble understanding written language or pictures, because visual information is not processed and transmitted to Wernicke’s area.

auditory association areas word deafness LESION FAETURES auditory association areas word deafness visual association areas word blindness called dyslexia Wernicke's Aphasia Global Aphasia unable to interpret the thought Sensory Aphasia Broca's Area Causes Motor Aphasia

GLOBAL APHASIA (CENTRAL APHASIA) This means the combination of the expressive problems of Broca's aphasia and the loss of comprehension of Wernicke's. The patient can neither speak nor understand language. It is due to widespread damage to speech areas and is the commonest aphasia after a severe left hemisphere infarct. Writing and reading are also affected.

DYSARTHRIA DISORDERED ARTICULATION Slurred speech. Language is intact Paralysis, slowing or incoordination of muscles of articulation or local discomfort causes various different patterns of dysarthria. Examples the monotone of Parkinson's disease (Slurred), speech in myasthenia that fatigues and dies away. Many aphasic patients are also somewhat dysarthric.

WIDESPREAD DAMAGE TO SPEECH AREAS APHASIA EXPRESSIVE RECEPTIVE NON FLUENT BROCA'S AREA WERNICK’S AREA CONDUCTION APHASIA FLUENT ANOMIC ANGULAR GYRUS WIDESPREAD DAMAGE TO SPEECH AREAS GLOBAL

Speech aparatus Air must be pushed through vocal tract to produce sound. System must control precisely the shape of the vocal tract. Does so by modulating behaviour of 3 subsystems.

Respiratory subsystem Respiratory subsystem (power system) Controls the diaphragm and external intercostals to inhale Internal intercostals: most important respiratory muscles for speech - propel air out (exhale) - control speech volume by regulating the amount of pressure

Laryngeal mechanism (sound source) Regulates pitch by changing the stiffness of the vocal chords Modulates aspiration Allows for whispering Creates voicing (e.g., “v” versus “f”)

Articulatory subsystem Responsible for the remaining distinctions of speech Structures: mouth, jaw, lips, nasal tract, velum (flap connecting nasal tract and oral cavity) and pharynx

Articulatory subsystem Articulatory subsystem (acoustic filter) Pharynx: shape produces different vowels; human infants, pre-human hominids and apes have short necks, high larynx and small immobile throats, so unable to produce vowels (but also can’t choke).