Nervous System Physiology By Dr. SHAHAB SHAIKH PhD MD MBBS Lecture – 12: Speech •••••••••••••••••••••••••••••••••• Faculty of Medicine Al Maarefa Colleges of Science & Technology

SPEECH Speech is complex form of communication in which spoken words convey ideas. Verbal behaviors constitute one of the most important classes of human social behavior. Language is one of the fundamental bases of human intelligence and a key part of human culture.

SPEECH Broca’s area Wernicke’s area Speech Centers: motor speech area Wernicke’s area sensory speech area Both connected by Arcuate Fasciculus. Both areas also interact with association areas.

SPEECH Broca’s area It is located in left frontal lobe just front of the base of the Primary motor cortex. It is for Articulation – Word formation Broca’s area contains motor memories — in particular, memories of the sequences of muscular movements that are needed to articulate words. Broca's area excites Motor area which controls the muscles necessary for articulation.

SPEECH Wernicke’s area 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). It plays important role in understanding of both spoken and written messages. Wernicke’s area receives input from visual cortex in the occipital lobe and also auditory cortex in temporal lobe.

SPEECH Arcuate Fasciculus Is a axon pathway between Wernicke’s area and Broca’s area Higher-Order Association Cortex Wernicke’s area has connections with various association areas in … Left Frontal Left Temporal Left Parietal Are involved with mediating between concepts and language

SPEECH

SPEECH

PATHWAY FOR HEARING & SPEAKING Steps are: Reception in the primary auditory cortex area of sound signals. Interpretation of words in Wernicke's area. Determination of thoughts in words to be spoken in Wernicke’s area. 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.

PATHWAY FOR HEARING & SPEAKING

PATHWAY FOR READING & THEN SPEAKING Steps are: Reading the words – reception in primary visual area. Information passes through angular gyrus region and reaches Wernicke's area. Interpretation of words in Wernicke's area. Determination of thoughts in words to be spoken in Wernicke’s area. 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.

PATHWAY FOR READING & THEN SPEAKING

SPEECH Lateralization: Speech area are located in one sphere (on one side), usually the dominant hemisphere. Left hemisphere is dominant for fine movements in most Right handed people. Also in many Left handed people. Left hemisphere is therefore called DOMINANT SPHERE. 90% of left handed people have left cerebral hemisphere as dominant also.

SPEECH Although the circuits that are primarily involved in speech comprehension and production are located in one hemisphere (almost always, the left hemisphere), the Right hemisphere does have its role in speech. Damage to the right hemisphere makes it difficult for a person to read maps, perceive spatial relations, and recognize complex geometrical forms. The right hemisphere also appears to be involved in organizing a narrative—selecting and assembling the elements of what we want to say. The right hemisphere is involved in the expression and recognition of emotion in the tone of voice.

SPEECH DISORDERS Thus Damage to the specific regions of brain can result in selective disturbance of speech. Damage to Brocas’s area (motor aphasia) Damage to Wernicke’s area (sensory aphasia) Damage to ARCUATE FACICULUS (Conduction aphasia) Speech Disorders of Articulation (Dysarthria)

SPEECH DISORDERS Damage to Brocas’s area: (motor aphasia) It results in failure of word formation, but patient can understand the spoken and written words. These people know what they want to say, but can not express themselves. This disorder is characterized by slow, laborious, and non-fluent speech. But although they often mispronounce words, the ones the patients manage to come out with are usually meaningful. Broca (1861) suggested that this form of aphasia is produced by a lesion of the frontal association cortex, just anterior to the face region of the primary motor cortex. Subsequent research proved him to be essentially correct, and we now call the region Broca’s area. Broca’s aphasia is much more than a deficit in pronouncing words. In general, three major speech deficits are produced by lesions in and around Broca’s area: agrammatism, anomia, and articulation difficulties.

SPEECH DISORDERS Damage to Wernicke’s area: (sensory aphasia) These patients can not understand the words they hear or see. what they say is full of jargon and neologisms that make little sense. They can speak fluently, their articulation is perfect, but their speaking makes no sense because they can not attach meaning to words to convey their thoughts.

SPEECH DISORDERS Anomic aphasia (anomia): is a type of aphasia characterized by problems recalling words, names, and numbers. Subjects often use circumlocutions (speaking in a roundabout way) in order to avoid a name they cannot recall or to express a certain word they cannot remember. Damage to angular gyrus

SPEECH DISORDERS Conduction Aphasia: Patients may be able to understand speech as well as produce meaningful speech, but have difficulty repeating a spoken sentence. Often associated with damage to the Arcuate Fasciculus, which connects Wernicke’s area with frontal pre-motor structures.

SPEECH DISORDERS Global Aphasia - Damage occurs to both broca’s area and Wernicke's area. Patient can not understand or speak.

SPEECH DISORDERS Area of Lesion Features Wernicke's Area Sensory Aphasia Broca's Area Motor Aphasia Dominant Hemisphere (Brocas & Wernickes both) Global Aphasia Arcuate Fasciculus Conduction Aphasia Angular Gyrus Anomic Aphasia Auditory asson area Word deafness Visual asson areas Word blindness (dyslexia)

SPEECH DISORDERS Speech Disorders of Articulation (Dysarthria) occurs due to weakness of articulating muscles in-coordination of articulating muscles Mechanical factors Ill fitting dentures Weakness of oro-lingual muscles concerned with speech Problem may be in muscle, nerve supply or cerebellum Cerebellar lesions causes dysarthria, speech is with increased word length. it is called scanning speech. Dysarthria in Parkinsonism (basal ganglia) Speech is monotonous, slurring dysarthria

SPEECH DISORDERS Dysphonia: In Dysphonia, sound is not pronounced properly. Dysphonia is usually due to laryngeal problem.

SPEECH DISORDERS STAMMERING SPEECH: 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 2½ to 3 ½ years. Factors which precipitate – stress. Majority of children grow out of it but in some it remains and requires speech therapy.

DYSLEXIA Dyslexia is difficulty in learning due to auditory reception (word deafness) or visual reception (word blindness). It is developmental problem where connection between visual and speech area of cortex is faulty – “faulty wiring”. In dyslexia, there is no intellectual problem.

SPEECH DISORDERS 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.

SPEECH DISORDERS 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.

References Human physiology by Lauralee Sherwood, 8th edition Text Book Of Physiology by Guyton & Hall, 11th edition

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