Mental Retardation


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Mental Retardation

  1. 1. CHAPTER 13 Intelligence And Cognitive Functioning Deficiencies and Disorders of Intelligence
  2. 2. Developmental disabiliteis and mental retardation • The criteria for retardation =arbitrary, and based on judgments about the abilities required to get along in our complex world. – In 1978, then 1994 the American Psychiatric Association set the criteria for retardation as a combination of an IQ below 70 points and difficulty meeting routine needs like self-care. – Prior to that, cut off was 85 – “cured” thousands of individuals • Not only is any definition arbitrary, but it is situational and cultural as well. – A person considered retarded in our society might fare reasonably well in a simpler environment. – 6-hour retarded child
  3. 3. Developmental disabiliteis and mental retardation • MANY causes of retardation • Retardation can be inherited or due to improper cell division – Fragile X – Tay Sachs – Williams Syndrome – Prader Willy – Down Syndrome • Retardation can be caused by diseases contracted during infancy – Meningitis; infection, etc. – prenatal exposure to viruses such as rubella (measles).
  4. 4. Developmental disabiliteis and mental retardation • Can be due to teratogen exposure – Maternal alcoholism is now the leading cause of mental retardation – Other drugs • Can be caused by prematurity – 50% of preterm infants have significant disability – Two most common: Cerebral palsy and mental retardation • What about autism? – Used to be generically called retardation – Now identify it as separate disorder – Many of individual who would have been diagnosed as retarded are now labeled autistic
  5. 5. Down syndrome • Down syndrome usually caused by – the presence of an extra 21st chromosome, – Mosaicism: chromosome splits into many small parts – Trisomy 21: chromosonal split resembles presence of 3 21st chromosomes – Related to maternal age, but not necessarily caused by age • Typically results in individuals with IQs in the 40 to 55 range. – Early intervention critical – Early that begin intervention, typically higher the IQ • Amyloid precursor protein gene that involved in early-onset Alzheimer’s disease is located on chromosome 21 – was discovered because Down syndrome individuals also develop amyloid plaques. – 95% of people with Down syndrome have the entire extra chromosome – In a few cases: only an end portion is present, and attached to another chromosome.
  6. 6. Phenylketonuria • Phenylketonuria or PKU – due to an inherited inability to metabolize the amino acid phenylalanine. – excess phenylalanine interferes with myelination during development. • Without dietary treatment – the individual is severely or profoundly retarded – an adult IQ of around 20 points. • Much more rare today: Postnatal blood tests and routine hospital screenings followed by dietary changes has greatly reduced incidence in this country.
  7. 7. Other causes of retardation • Hydrocephalus – Water on the brain – occurs when cerebrospinal fluid builds up in the cerebral ventricles. – The increased fluid volume crowds out neural tissue, usually causing retardation. • Hydrocephalus can be relatively easily treated if caught early – installing a shunt that prevents the accumulation of the excess cerebrospinal fluid. – Eliminate or greatly reduce likelihood of long term brain damage
  8. 8. autism • Autism is a disorder that typically includes – compulsive, ritualistic behavior – impaired sociability – Language deficits – Often to usually: mental retardation. • Autism is one of 5 autism spectrum disorders – Autism, classic autism, high functioning autism – Autistic Disorder – Asperger Syndrome or Asperger's Disorder – Pervasive Developmental Disorder (PDD), – Autism Spectrum Disorder (ASD).
  9. 9. autism • Autism diagnosis given based on – Number and particular kinds of symptoms – Severity - mild to severe – Age of onset – Levels of functioning – Challenges with social interactions • Autism is the most common neurological disorder affecting children and one of the most common developmental disabilities •
  10. 10. autism • Asperger’s syndrome – is the most similar to autism – most likely to share common causes. • People with Asperger’s syndrome are – socially impaired – display repetitive movements – preoccupations with narrow interests like autistic individuals, – But language and cognitive development and self help skills are more normal.
  11. 11. Autism: Common core of impairment • Whether retarded or not, autistic individuals share a common core of impairment in – Communication: often difficulty with communication – Imagination: very literal – Socialization: poor social skills • May be mute or show delayed language development – have trouble understanding verbal and nonverbal communication. – Again, very literal and concrete • Much of social behavior problem may be because autistic person lacks a theory of mind – ability to attribute mental states to oneself and to others. – An individual with autism cannot infer what other people are thinking.
  12. 12. Theory of mind • Two hypotheses as to how we develop a theory of mind. – “theory theory:” We build hypotheses over time based on our experience. – Simulation theory: We gain insight into people’s thoughts and intentions by mentally mimicking the behavior of others. • Data tends to support simulation view: – Existence of mirror neurons – Poor imitation skills in individuals with autism – Very different from Williams syndrome
  13. 13. How does poor mirror function affect intelligence? • Impaired mirror functions reduces the autistic person’s ability to – Empathize – learn language through imitation. • For example, some individuals with autism show no mirror neuron activity while – imitating facial expressions – or when observing a model’s hand movements. • Other studies show reduced activation in the inferior frontal cortex and motor cortex, – Suggests weakness in the dorsal stream connections – Provide important input to those areas containing mirror neurons.
  14. 14. Superior abilities? • Savant – person with exceptional intellectual skills – beyond the level of “ordinary” genius, like Leonardo da Vinci or Albert Einstein. – term is more frequently used to describe individuals who have one or more remarkable skills but whose overall functioning is below normal. – • Half of these individuals with islands of exceptional capabilities are autistic savants.
  15. 15. How can you be retarded and superior? • The source of the autistic savant’s enhanced ability is unknown. • Dehaene (1997): – may be due to intensely concentrated practice, – more typically the skill appears without either practice or instruction – Suggests innate ability. • Ramachandran and Blakeslee (1998): specialized area of the brain becomes enlarged at the expense of others. • Snyder and Mitchell (1999): – savant capabilities within us all, – are released when brain centers that control executive or integrative functions are compromised. – Brain damage studies lend support this hypothesis
  16. 16. Brain areas affected in autism • Subtle but widespread brain anomalies have been found, • Especially in the – brain stem, – the cerebellum, – temporal lobes. – The location of damage is inconsistent, which may mean only that there are various pathways to autism. • What causes these brain defects? – is uncertain, – at least we know they occur early, during brain development – So: know where and when to look for the answer. – NOT caused by parental rejection!
  17. 17. Autism and environmental influence • Environmental influence: Teratogens? – received the most public attention – generated the greatest controversy is vaccines, • either the MMR vaccine (for measles, mumps, and rubella) • Or mercury as a vaccine preservative. – Research does not support this hypothesis. • Another possibility: Brain damage = autoimmune reaction. – A likely source for such an autoimmunity is viral diseases like measles. – Immune system attacks brain – Could easily be genetic/familial
  18. 18. What DO we know? • Elevated serotonin levels – biological or biochemical abnormality most consistently found in autistics – One of the genes suspected of playing a role in autism = responsible for the mechanism involved in serotonin reuptake. • Serotonin drugs improve functioning in autism – Supports 5HT model – Changes in serotonin activity suggests that SSRI therapeutic effect is in producing compensatory changes in receptor activity.
  19. 19. What DO we know? • Oxytocin referred to as “sociability molecule” • Affects social behavior and bonding in lower animals. • Autistic children were found to have lower levels of oxytocin than normal controls, – this difference pronounced in the autistic children who were described as aloof. – Thus, may be that low levels of oxytocin are involved – Interestingly, Williams syndrome kids have HIGHER levels than normal – with-williams.html – • May be in the eyes: – Interest in eyes related to oxytocin levels – Individuals with autism avoid eye contact – Individuals with Williams syndrome seek out eye contact
  20. 20. Is autism “genetic’ or inherited? • Siblings of autistics are 40 to 60 times more likely to be diagnosed with autism than other children. – The number would be even higher, but parents tend to stop having children after the first autistic diagnosis. – Suggests strong familial, if not genetic, link • Autism occurs two to four times more frequently in males than in females, – suggests that the genes for autism might be on the X chromosome – Currently: at least four areas on the X chromosome that are potential sites for autism genes.