Viewpoint on the Brain Disorder in Autism
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(section links):
Introduction
I. BRAIN DAMAGE AT BIRTH
1 - Asphyxia at Birth
2 - Hypoxic Birth
3 - Asphyxia Versus Hypoxia
4 - Human Conditions
5 - Stages of Asphyxia
6 - The Umbilical Cord Lifeline
7 - Developmental Delay
8 - Poor Manual Dexterity
9 - Progressive Degeneration
10 - Autism and Complications at Birth
11 - Mercury, and Other Toxic Factors
II. THE AUDITORY SYSTEM
12 - Metabolic Rank Order
13 - The Auditory System
14 - Auditory Dysfunction
III. LANGUAGE
15 - Language By Ear
16 - Verbal Auditory Agnosia
17 - Echolalic Speech
18 - Echolalic Speech is Pragmatic
IV. CHILDHOOD HANDICAPS
19 - Auditory and Motor Handicaps
20 - Increased Incidence of Autism
21 - Fetal to Postnatal Adaptation
22 - Forgotten History
23 - Worth Remembering
24 - Hemoglobin
25 - Infant Anemia
26 - Autism in Twins
27 - Male-Female Differences
V. BRAINSTEM DAMAGE
28 - Variable Vulnerability
29 - Patterns of Damage
30 - Wernicke's Encephalopathy
31 - Suffocation at the Molecular Level
32 - Thiamine Deficiency
33 - Brain-Gut Relationship
VI. REFERENCES (for all sections)
34 - Bibliography (for section III)
35 - Autism and Complications at Birth
36 - Umbilical Cord Clamping
Summaries (for all sections)
Summaries (for section III)
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Overview (Language):
The brainstem auditory pathway is the earliest system to be myelinated and functional; the human fetus responds to sounds by 29 gestational weeks. Myelination and maturation of the language circuits of the cerebral cortex are not complete until the third or fourth postnatal year. Nevertheless, children normally begin to speak between the first and second year of life, and even easily learn a second language by ear in a foreign language environment.
The normal child hears and repeats stressed syllables, and early speech begins with use of short units of meaning, which the child quickly learns to rearrange to fit new contexts. An autistic child on the other hand makes use of parroted phrase fragments, without awareness of syllable based units of meaning. Whole phrases and sentences are spoken in new contexts without rearrangements to better match new situations. It is proposed here that children with autism do not hear syllable boundaries and are thus unable to detect small units of meaning required for normal language development.
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Language evolved in the human brain with the temporal-to-frontal lobe circuit in the cerebral cortex. Language is a higher cortical function. However, language learning begins before maturation of the cortical language areas is complete. Children learn language "by ear."
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Maturation of brain circuits takes place as myelin sheaths form around axons of neurons. The brainstem auditory pathway is myelinated and functional earlier than any other system in the human brain [1-3].
Figure 12 is from the brain of a human infant born prematurely at 29 gestational weeks (29gw) who survived eight postnatal days (8pnd). The dark stain for myelinated fibers in the auditory pathway dominate the brainstem almost to the exclusion of other neural systems (ICol, inferior colliculus; LLm, lateral lemniscus; MLF, medial longitudinal fasciculus; MLm, medial lemniscus).
It is at 29 gestational weeks that the human fetus first responds to sounds [3].
A maturational timetable can be viewed by clicking the link above to The Auditory System. Myelination of the acoustic radiations to the temporal lobes continues up to three or four years of age. But children normally start learning to speak between the ages of one to two.
Brown and Bellugi (1964) determined that young children normally recognize stressed syllables as a prominent feature of speech around them.
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Figure 12: The brainstem auditory pathway is myelinated earlier in the human fetus than any other circuit of the brain.
(from Yakovlev & Lecours, 1967, with permission from Blackwell Scientific Publications).
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Detection of stressed syllables leads to a predictable first stage of language development known as "telegraphic speech" in which a child makes use of single syllable units of meaning and rearranges these newly acquired units of meaning to fit new contexts [4-6].
Inability to recognize syllable and word boundaries has been identified as a problem in some children with autism [7]. Use of phrase fragments rather than syllabic units is characteristic of the echolalic speech of autistic children. Phrase fragments are not as easily rearranged as syllabic units to fit new contexts.
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Everyone agrees learning a language by ear is best, but after the first decade of life this becomes more and more difficult. Normal young children can learn a second language, without accent. The ability to hear syllable and word boundaries decreases with age. There is evidence that the auditory system ages faster than other areas of the brain because of its high metabolic rate [8]. Impairment of the inferior colliculus by asphyxia at birth may be like premature aging, and make it as difficult for a child so handicapped to detect syllable and word boundaries as it is for an adult trying to learn a foreign language.
Rapin (1997) suggested that inability to distinguish syllable and word boundaries in rapid streams of speech may be the basis of the language disorder in some children with autism; she referred to this as "verbal auditory agnosia" [7]. Agnosia is a failure of recognition without loss of sensory function. Most children with autism have hearing seemingly adequate for learning language, but agnosia ought to be more fully explored.
Agnosia for speech or "word deafness" (loss of ability to comprehend spoken language) has been reported in three previously normal adults following injury of the inferior colliculi in the midbrain auditory pathway [9-11].
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Telegraphic speech includes use of elemental units of meaning rearranged to fit new contexts. Some examples are phrases like "Mommy go store" or "Apple, I want." Use of elemental units of meaning (morphemes) reveals a child's ability to parse what he hears. Command of morphemic components facilitates re-wording and comprehension of grammatical structures.
Speech productions of an autistic child on the other hand at best consist of phrase fragments used badly out of context. This is echolalic speech, use of parroted "sound bytes," which Kanner (1946) referred to as "irrelevant and metaphorical language" [12]. No rewording to fit new contexts takes place. "Pronoun reversal" is part of the failure to re-word, as is frequent use of the prosodic intonation for a question.
"You don't want to go swimming?" is not intended as a question, but as a statement by the child that he doesn't want to go in the water. "You want an apple?" is equivalent to the telegraphic request "Apple, I want." "Is that yours?" is equivalent to a normal young child's statement, "That mine."
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Figure 13:Conrad and Ralf getting ready for bedtime stories (after getting the toothpaste unstuck).
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Reliance on echolalic sound-bytes impedes recognition of morphemic units or grammatical structures. But echolalic speech is not irrelevant and metaphorical. Echoed phrases are used with pragmatic purpose, for communication or expression of feelings. Often only the intimate caregiver can explain the utterances of an autistic child.
"What's the matter, did your wagon get stuck?" was a phrase my son Conrad used in any frustrating situation. His grandmother did not understand why he should say this when he was having trouble squeezing toothpaste out of the tube.
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"He speaks perfectly well," my mother said, "He just doesn't make any sense!"
I had to explain to her where this peculiar phrase came from. At least a few weeks (if not months) earlier Conrad was pulling his little wagon along the fence in our backyard, and started to cry when it got stuck on the root of a shrub.
His brother Ralf went running to help calling out, "What's the matter, did your wagon get stuck?"
Conrad remembered this as the best fit he had for any context of frustration, or as Roger Brown (1975) said, it was the equivalent of saying "Damn" [6].
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Figure 14: Ralf and the wagon that got stuck.
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Early Myelination and Maturation of the Auditory System
[citations 140-142 in full bibliography]
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Langworthy OR (1933) Development of behavior patterns and myelinization of the nervous system in the human fetus and infant. Contributions to Embryology, no. 139 24:1-57.
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Yakovlev PI and Lecours A-R (1967) The myelogenetic cycles of regional maturation of the brain. In A. Minkowski (Ed.), Regional Development of the Brain in Early Life (pp. 3-70). Oxford: Blackwell Scientific Publications.
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Moore JK, Perazzo LM, Braun A (1995). Time course of axonal myelination in the human brainstem auditory pathway. Hearing Research 87:21-31, 91:208-209.
Back to: Language By Ear, [Top]
Stressed Syllables and Learning to Speak
[143-145 in full bibliography]
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Brown R, Bellugi U (1964) Three processes in the child's acquisition of syntax. Harvard Educational Review 34:133-151.
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Brown R (1973) A First Language: The Early Stages. Cambridge, MA: Harvard University Press.
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Brown R (1975) A collection of words and sentences, an autistic child. In R Brown RJ Herrnstein, Psychology (pp. 444-449). Boston: Little, Brown and Company.
Back to: Language By Ear, Echolalic Speech, [Top]
Verbal Auditory Agnosia [146 in full bibliography]
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Rapin I (1997) Autism. New England Journal of Medicine 337:97-104.
Back to: Language By Ear, Verbal Auditory Agnosia, [Top]
Early Aging of the Auditory System [147 in full bibliography]
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Uecker A, Gonzalez-Lima F, Cada A, Reiman EM. Behavior and brain uptake of fluorodeoxyglucose in mature and aged C57BL/6 mice. Neurobiol Aging. 2000 Sep-Oct;21(5):705-18.
Back to: Verbal Auditory Agnosia, [Top]
Verbal Auditory Agnosia Following Damage of the Inferior Colliculi
[148-150 in full bibliography]
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Meyer B, Kral T, Zentner J. (1996) Pure word deafness after resection of a tectal plate glioma with preservation of wave V of brain stem auditory evoked potentials. Journal of Neurology, Neurosurgery and Psychiatry. 61:423-424.
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Johkura K, Matsumoto S, Hasegawa O, Kuroiwa Y. (1998) Defective auditory recognition after small hemorrhage in the inferior colliculi. Journal of the Neurological Sciences. 161:91-96.
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Masuda S, Takeuchi K, Tsuruoka H, Ukai K, Sakakura Y. (2000) Word deafness after resection of a pineal body tumor in the presence of normal wave latencies of the auditory brain stem response. The Annals of otology, rhinology, and laryngology. 2000 Dec;109(12 Pt 1):1107-1112.
Back to: Verbal Auditory Agnosia, [Top]
Irrelevant and Metaphorical Language [151 in full bibliography]
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Kanner L (1946) Irrelevant and metaphorical language of early infantile autism. American Journal of Psychiatry 103:242-246.
Back to: Echolalic Speech, [Top]
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15 - Language by Ear
Most children learn language by ear. Language learning begins before the language circuits of the temporal and frontal lobes are fully myelinated and mature. Children normally learn language through recognition of stressed syllables, which leads to the well recognized stage of language development known as "telegraphic speech" (baby talk).
16 - Verbal Auditory Agnosia
"Agnosia" is a failure of recognition in the apparent absence of sensory deficit. Agnosia for speech sounds has been reported in some children with autism, and has been termed "verbal auditory agnosia." At least three cases of verbal auditory agnosia have been reported in adults following damage of the inferior colliculus.
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17 - Echolalic Speech
Some children with autism begin to use parroted phrase fragments (echolalic speech) at the time most children are at the "telegraphic speech" stage of development. The child who hears syllable boundaries is able to detect small units of meaning (morphemic units), to recognize their recurrence in the speech of those around him, and eventually to rearrange their use in new contexts. Use of phrase fragments indicates failure to detect syllable boundaries, and again raises the issue of auditory dysfunction in autism.
18 - Echolalic Speech is Pragmatic
Kanner (in 1946) referred to the echolalic speech of autistic children as "irrelevant and metaphorical speech." The irrelevant nature of echolalic speech is because of its use out of context; its partial fit to context makes it seem metaphorical. Phrase fragments are not as easily rearranged as morphemic units to fit context. "You don't want to go swimming?" was not a question, but one autistic child's emphatic statement that she didn't want to go in the water; this statement also provides an example of "pronoun reversal."
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END
Revision:
January 20, 2023 06:44 PM
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