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What is Speech ?
Speech is complex form of communication in which spoken words convey ideas.
When we speak, first we understand.
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For understanding and speaking, we have two speech centers:
1. Broca’s area – motor speech area
2. Wernicke’s area – sensory speech area
Both are connected by ARCUATE
FASCICULUS.
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How we speak?
Because of speech centers and articulation of muscles of speech.
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1.
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Broca’s area
It is located in left frontal lobe in close association with motor areas of the cortex.
It is for speaking– Word formation
Brocas area simultaneously excites
Motor area which controls the muscles necessary for articulation.
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2. Wernicke’s area
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It is located in the left cortex at Superior gyrus of Temporal lobe at the juncture of parietal, temporal and occipital lobes.
It is concerned with language comprehension (understanding).
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It plays important role in understanding of both spoken and written messages.
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2. Wernicke’s area
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It is also responsible for formulating coherent pattern of speech, that are transferred via bundle of fibers ARCUATE
FASCICULUS to brocas’s area.
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Wernicke’s area receives input from visual cortex in the occipital lob and also auditory cortex in temporal lobe.
It also gets information from somatosensory cortex.
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Steps are:
1.
Reception in the primary auditory cortex
2.
3.
area of sound signals.
Interpretation of words in Wernicke's area.
Determination of thoughts in words to be spoken in Wernicke’s area.
4.
5.
6.
Transmission of signals from Wernicke’s area to Broca’s area by Arcuate fasciculus.
Word formation in Broca’s area.
Transmission of signals to motor cortex to control the speech muscles.
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Steps are:
1.
Reading the words – reception in primary visual area.
2.
Information passes through angular gyrus region and reaches Wernicke's area.
Step 3 to Step 6 are same for speaking as in response to hearing words.
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Speech area are located in one sphere
(on one side), usually left hemisphere.
Left hemisphere is also dominant for fine movements).
Left hemisphere is therefore DOMINANT
SPHERE.
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Right handed people have speech center in left hemisphere i.e Dominant hemisphere
90% of left handed people have left cerebral hemisphere as dominant also.
10% of left handed people have right hemisphere as dominant for speech.
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Most people are right handed, as left side of the brain controls the right side of the body.
Left cerebral hemisphere – excels in logical, analytic, and verbal task e.g. math, language forms, philosophy.
Left cerebral dominance is associated with thinkers.
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Right cerebral hemisphere
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It excels in non-language skills e.g. artistic and musical talents.
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Therefore, right hemisphere dominance is associated with creators.
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Damage to the specific regions of brain can result in selective disturbance of speech.
We will discuss
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Damage to Brocas’s area (motor aphasia)
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Damage to Wernicke’s area (sensory aphasia)
Damage to ARCUATE FACICULUS
Speech Disorders of Articulation
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Speech disorders – two main groups
1. Dysphasia – disorder of language area in the dominant hemisphere.
2. Disorders of articulation (dysarthria) and disorders of phonation (dysphonia).
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Damage to Brocas’s area (motor aphasia)
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It results in failure of word formation, but patient can understand the spoken and written words (as Wernicke’s area is functioning).
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These people know what they want to say, but can not express themselves.
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Damage to Brocas’s area
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They can not establish the proper motor command to articulate the desired word, even though they can move their lips and tongue.
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Damage to Wernicke’s area (sensory aphasia)
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These patients can not understand the words they hear or see.
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They can speak fluently, their articulation is perfect, but their speaking makes no sense.
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WHY ?
Because they can not attach meaning to words to convey their thoughts.
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Damage to ARCUATE FACICULUS
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Striking defect is inability to repeat phrases or words spoken by the examiner. It is called CONDUCTION
APHASIA.
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Global Aphasia
- Damage occurs to both broca’s area and Wernicke's area.
Patient can not understand or speak.
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Speech Disorders of Articulation
(Dysarthria)
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They occur due to
- weakness of articulating muscles
- in-coordination of articulating muscles
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Dysarthria can be
i) Mechanical factors
- ill fitting dancher
ii) Weakness of orolingual muscles concerned with speech
Problem may be in muscle, nerve supply or cerebellum
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1. Cerebellar disease cause speech, with increased word length.
Ask patient to say constitution, he will say cons-ti-tu-tion, it is called scanning speech.
2. Parkinsonism (basal ganglia)
- Speech is monotonous, slurring dysarthria
Dysarthric speech is difficult to understand.
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In Dysphonia, sound is not pronounced properly.
Dysphonia is usually due to laryngeal problem.
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1.
2.
3.
4.
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Damage of Broca’s area – motor, non-fluent aphasia.
Damage to Wernicke’s area – sensory aphasia, fluent speech but having no sense.
Global aphasia – both motor and sensory speech are lost (damage to broca’s and Wernicke's area).
Damage to Arcuate fiber – conduction aphasia.
Dysarthria – articulation affected.
Cerebellar disease – scanning speech.
Parkinsonism – slurred, monotonous speech.
Myasthenia gravis – speech fatigue, speech dies away.
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It is a speech disorder, where person prolongs the word usually at vowels
(a,e,i,o,u).
e.g. To-to-to-to-morrow
Mmmmmmm ilk
Commonly occurs by age of 2 ½ to 3 ½ years.
 Factors which precipitate – stress.
 Majority of children grow out of it but in some it remains and requires speech therapy.
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Dyslexia is difficulty in learning due to auditory reception (word deafness) or visual reception (word blindness).
What is the cause?
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Because it is developmental problem where connection between visual and speech area of cortex is faulty – “faulty wiring”.
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In dyslexia, there is no intellectual problem.
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Speech center is found in one hemisphere i.e. left side.
But if a child below 2 years has damage to left cerebral hemisphere then language function are transferred to right hemisphere with no delay in language development.
This is due to plasticity or remodeling of brain in response to varying demands. It is due to formation of new neural pathways or connections (not new neurons).
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Up to the age of 10 years, if damage occurs to left hemisphere, language activity can be re-established in the right hemisphere after a temporary period of loss.
After 10 years, there may be permanent loss of speech as regions of brain involved in spoken and understanding speech are permanently assigned before 13 to 15 years.
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Infants can distinguish and articulate the entire range of speech, but each language uses only portion of these sounds.
As child matures, they often loose the ability to distinguish or express speech sounds that are not important in their native language.
Therefore, child learns any language e.g.
Arabic, English, Japanese..etc, which is taught to them.
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