Professor, Department of Physiology, PSMC, Karamsad Learning Objectives • What is Speech? • Role of categorical hemisphere • Development of Speech • Speech areas and their role in speech • Language disorders (Aphasia) What is speech? • Speech is a method of communication. It involves: 1. Hearing 2. Vision 3. Speaking 4. Reading 5. Writing 6. Sometimes, even silence is the best speech. What is speech? • Most of the speech is acquired, requiring conscious effort, but it may also occur subconsciously in small amount. • Speech is the expression of thoughts and ideas by speaking or by writing. • The categorical hemisphere is concerned with language(Speech) functions. Categorical hemisphere and language function • In 96% of right-handed individuals, who constitutes 91% of the human population, the left hemisphere is the dominant or categorical hemisphere.
• In the remaining 4% of right-handed individuals, the
right hemisphere is dominant.
• In 15% of left-handed individuals, the right
hemisphere is dominant, but, in the remaining70% of left-handers,left hemisphere is dominant. Categorical hemisphere and language function • In majority of humans, left cerebral hemisphere is the dominant or categorical hemisphere.
• It is concerned with language (speech),
reasoning, mathematical calculations, numerical and scientific skills.
• Right hemisphere is more concerned with
recognition of faces, music, art, and emotions. Development of language or speech 1. The potential for development of language-specific mechanisms in the left hemisphere is present at birth.
2. The assignment of language functions to specific
brain areas is fairly flexible in the early years of life before puberty.
3. Damage to the perisylvian area of left hemisphere
during infancy or early childhood, causes temporary, minor language impairment, but similar damage in adults causes permanent speech defects. Development of language or speech 1. If the left hemisphere is traumatized in older children, functional language ability may be reestablished to some extent in the right hemisphere. Language develops in these children.
2. By puberty, the transfer of language
functions to the right hemisphere is less successful, and language skills are lost permanently. Speech areas and their role in speech • Normal Speech actually requires practically all areas of cerebral cortex, but 4 areas are crucial for the development of normal speech:
• Broca’s speech area(Area 44) or Motor
speech area • Wernicke’s speech area(Area 22) or General interpretative area • Angular gyrus (Area 39) • Arcuate fasciculus Speech areas Speech areas involved in speaking a heard word Pathway for speaking a heard word Speech areas involved in speaking a written word Pathway for speaking a written word Cortical areas involved in speech Functions of Wernicke’s area • A region at the posterior end of the superior temporal gyrus in the categorical hemisphere is called as Wernicke’s area(General Interpretative Area)
• Comprehension of auditory and visual
information(to understand the question and what to answer)
• Formation of thoughts to be expressed
• Choice of words to be used
Functions of Broca’s area • Broca’s area is situated in the frontal lobe immediately in front of the inferior end of the motor cortex
• Broca’s area processes the information
received from Wernicke’s area into a detailed and coordinated pattern for vocalization
• It then projects the motor pattern of
vocalization via a speech articulation area in the insula to the motor cortex Function of motor cortex in speech • Motor cortex (area 4) initiates the contraction of muscles responsible for appropriate movements of the lips,tongue,soft palate, larynx and respiratory muscles to produce sound.
• The areas involved in speech and hand
movements are specially large in the motor cortex; use of the pharynx, lips, and tongue to form words are activities in which humans are especially skilled. Function of angular gyrus(Area 39) • It is situated behind the Wernicke’s area
• Angular gyrus is responsible for interpretation
of meaning of written words,pictures,and various objects.
• It also 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. Role of cerebellum in speech 1. The cerebellum is important in speaking and writing, which involve coordinated muscle contractions.
2. Cerebellar ataxia is manifest in defects of the
skilled movements involved in the production of speech, so that slurred, or scanning, speech results. Language disorders (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 (usually Left hemisphere).
• The most common cause is embolism or thrombosis
of a cerebral blood vessel(Stroke).
• ‘Aphasia' means a disturbance of the ability to use
language, whether in speaking, writing or comprehending. Classification of Aphasias 1. Non-fluent aphasia or expressive aphasia or Broca’s aphasia 2. Fluent aphasia (Wernicke’s aphasia) 3. Fluent aphasia (conduction aphasia) 4. Fluent aphasia (anomic aphasia)
• Writing is abnormal in all aphasias in which
speech is abnormal, but the neural circuits involved are unknown. Non-fluent aphasia • In nonfluent 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 (Expressive aphasia). Non-fluent aphasia • Damage to Broca’s speech area results in nonfluent aphasia, an inability to properly articulate or form words. • People with nonfluent aphasia know what they wish to say but cannot speak. • Speech therapy play an important role in rehabilitation of patient. • Speech therapy may improves patient’s communication with others. Fluent aphasia (Wernicke’s aphasia) • In this aphasia, the lesion is in Wernicke’s area • Speech itself is normal and sometimes the patient talk excessively. • However, what they say is full of jargon and neologisms that make little sense. • The patient also fails to comprehend the meaning of spoken or written words. • Speech therapy is of little value in these patients. Fluent aphasia(conduction aphasia) • Patients of conduction aphasia can speak relatively well and have good auditory comprehension but cannot put parts of words together or conjure up words. • Their prognosis is better as compared to a patient of Wernicke’s aphasia. • Conduction aphasia occurs due to lesions in and around the auditory cortex(areas 40,41.and 42). Anomic aphasia(angular gyrus aphasia) • When a lesion damages only angular gyrus (area 39), patient has no difficulty with speech or the understanding of auditory information. • Patient of anomic aphasia has difficulty in understanding written language or pictures, because visual information is not processed and transmitted to Wernicke’s area. • Patient is unable to name the object shown to him (anomic aphasia) Summary 1. Language is one of the fundamental bases of human intelligence and a key part of human culture. 2. Speech is a complex code that includes the acts of listening,reading,writing,and speaking 3. In 90% of the population the left hemisphere is specialized to produce language-the conceptualization of what one wants to say or write, the neural control of speaking or writing, and recent verbal memory. Summary • The development of language functions occurs in a critical period that closes at puberty. • After damage to the dominant hemisphere, some language function can be acquired by the opposite hemisphere– the younger the patient, the greater the transfer of function. • Aphasias are abnormalities of speech that are not due to defects of vision or hearing or to motor paralysis.