Language is one of the fundamental bases of human intelligence and a key part of human culture. Physiology of Language
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. It projects via the arcuate fasciculus to Broca’s area (area 44) in the frontal lobe. Anatomy of language areas
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 insula 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.
The probable sequence of events when a subject names a visual object (horizontal section of hum- an brain)
It is interesting that in individuals who learn a second language in adulthood, fMRI reveals that the portion of Broca’s area concerned with it is adjacent to but separate from the area concerned with the native language. However, in children who learn two languages early in life, there is only a single area involved with both.
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. The most common cause is embolism or thrombosis of a cerebral blood vessel. 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. The words retained are those which were being spoken at the time of the injury or vascular accident that caused the aphasia.
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 say is full of jargon and neologisms that make 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) atients can speak relatively well and have good auditory comprehension but cannot put parts of words together or conjure up words. 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.
Type of Aphasia and Site of Lesion Characteristic Naming Errors Nonfluent (Broca’s area) Fluent (Wernicke’s area) Fluent (areas 40, 41 and 42; conduction aphasia) conduction aphasia) Anomic (angular gyrus) “Tssair” “Stool” or “choss” (neologism) (neologism) “Flair... no, swair... tair” tair” “I know what it is... I have a lot of them” I have a lot of them” Aphasias. Characteristic responses of patients with lesions in various areas when shown a picture of a chair
AREALESION 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 CausesMotor Aphasia
Dyslexia which is a broad term applied to impaired ability to read, due to an inherited abnormality. which is a broad term applied to impaired ability to read, due to an inherited abnormality. Causes of Dyslexia: 1.Reduced ability to recall speech sounds, so there is trouble translating them mentally into sound units (phonemes). 2.There is a defect in the magnocellular portion of the visual system that slows processing and also leads to phonemic deficit. 3.There is decreased blood flow in angular gyrus in categorical hemisphere in both cases.
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.
Lesions limited to the left temporal pole (area 38) cause inability to retrieve names of places and persons but preserves the ability to retrieve common nouns. Stuttering, associated with right cerebral dominance and widespread overactivity in the cerebral cortex, cerebellum and supplementary motor area.
An important part of the visual input goes to the inferior temporal lobe, where representations of objects, particularly faces, are stored. In humans, storage and recognition of faces is more strongly represented in the right inferior temporal lobe in right-handed individuals, though the left lobe is also active. Lesions in this area cause prosopagnosia, the inability to recognize faces. They can recognize people by their voices, and many of them show autonomic responses when they see familiar as opposed to unfamiliar faces. However, they cannot identify the familiar faces they see.
DYSARTHRIA Slurred speech. Language is intact Paralysis, slowing or incoordination of muscles of articulation or local discomfort causes various different patterns of dysarthria. DISORDERED ARTICULATION Examples 'gravelly' speech of upper motor neurone lesions of lower cranial nerves, jerky, ataxic speech of cerebellar lesions (Scanning Speech), the monotone of Parkinson's disease (Slurred), speech in myasthenia that fatigues and dies away. Many aphasic patients are also somewhat dysarthric.
In the inferior portion of the left frontal lobe there is an area concerned with number facts and exact calculations. Frontal lobe lesions can cause acalculia, a selective impairment of mathematical ability. Accurate navigation in human 1.One is the right hippocampus, which is concerned with learning where places are located, 2.and the other is the right caudate nucleus, which facilitates movement to the places.
The greater brain weight of men is due to more neural components involved in getting from place to place and that this is why men resist asking directions when lost, whereas women do not hesitate to seek help.
Brain Areas Concerned with Language Wernick’s Area Broca’a Area Speech articulation Area in Insula Motor Cortex Angular Gyrus
ANOMIC NON FLUENT GLOBAL APHASIA FLUENT BROCA'S AREA WERNICK’S AREA CONDUCTION APHASIA ANGULAR GYRUS WIDESPREAD DAMAGE TO SPEECH AREAS EXPRESSIVE RECEPTIVE