section 6 - aetiology of adhd & autism

UN

DE

RG

RA

DU

AT

E

1

46

Lecturer: Simon Bignell

Section: 6 of 11

‘Autism, Asperger’s & ADHD’ (6PS055)

‘ADHD, Autism & Asperger’s’ (6PS077)

Aetiology of ADHD & Autism

UN

DE

RG

RA

DU

AT

E

2

46


Section: 6 of 11



Outline.

• What is ADHD?• Theories of ADHD.

– Response Inhibition Theory.• What is Autism?• Theories of Autism.

– Theory of Mind Deficit.– Executive Function Deficit.– Weak Central Coherence.– Systemizing-Empathizing / The Extreme Male Brain

UN

DE

RG

RA

DU

AT

E

3

46


Section: 6 of 11



Learning Outcomes of this Section.

On completion of the Section and with independent study you should be able to:

1. Understand the main causes/theories of Attention- Deficit/Hyperactivity Disorder and Hyperkinetic Disorder.

2. Understand the main causes/theories of Autism.

UN

DE

RG

RA

DU

AT

E

4

46


Section: 6 of 11



What Is ADHD?

ADHD is a developmental disability with a childhood onset that typically results in a chronic and pervasive pattern of impairment in school, social and/or work domains, and often in daily adaptive functioning.

UN

DE

RG

RA

DU

AT

E

5

46


Section: 6 of 11



What Is ADHD?

“No mental disability this decade has been assailed by as much criticism, scepticism and flat out mockery as ADHD.” Mathew Cohen.

• Problems of fine-tuning in the normal brain.

• Due to imbalance in neurotransmitters in parts of the brain responsible for self-monitoring.– Some would disagree with this (Hard to test!).

UN

DE

RG

RA

DU

AT

E

6

46


Section: 6 of 11



What Is ADHD?

• DSM-IV-TR - Three main subtypes: – Predominantly Inattentive Type

– Predominantly Hyperactive-Impulsive Type

– Combined Type

– ADHD not otherwise specified

ADHD.

ImpulsivenessImpulsiveness

InattentionInattention

Combined Combined typetype

Hyperactive- Hyperactive- Impulsive typeImpulsive type

InattentiveInattentive

typetype

HyperactivityHyperactivity

61%30%9%

UN

DE

RG

RA

DU

AT

E

8

46


Section: 6 of 11



Causes Of ADHD.

• The causes of ADHD are not fully known.– Likely to have multiple causes and complex interactions.– Good evidence for genetic component.– Evidence of structural and functional brain abnormality.

• The genetic contribution to these traits is routinely found to be among the highest for any psychiatric disorder (70–95% of trait variation in the population).– That’s nearly approaching the genetic contribution to human

height. (ICS, 2002).

UN

DE

RG

RA

DU

AT

E

9

46


Section: 6 of 11



Causes Of ADHD.No shortage of speculation concerning its aetiology, most of which

centres around the brain.

• About 10-15 percent of ADHD arises as a result of prenatal injuries to the development of the prefrontal cortex (Barkley, 2000).

• About 3-5 percent of ADHD arises as a result of post-natal brain damage from: trauma (head injury), streptococcal infections.

• About one in five ADHD children is an acquired case. They tend to be mostly boys.

– Because the male brain is more prone to injury, both pre-natally and post-natally than the female brain.

• About 70 neurochemicals in the brain:

– Dopamine and norepinephrine (still trying to work out which one).

– It may turn out that different subtypes of ADHD involve different balances between those two. .

UN

DE

RG

RA

DU

AT

E

10

46


Section: 6 of 11



Plausible causes of ADHD:– Likely a polygenetic contribution contributing at least

70% of the variance in symptom contribution.– Structural (corpus callosum, right hemisphere) and

total brain volume differences (approximately 3-5 per cent smaller).

– Differences in glucose metabolism in right pre-frontal cortex.

– Differences in sleep and waking EEG patterns.

Causes Of ADHD.

UN

DE

RG

RA

DU

AT

E

11

46


Section: 6 of 11



Other possible causes of ADHD:– Lead ingestion.– Mercury Poisoning.– MMR.– Stress.– Emotional problems.– Allergy.– Lack of essential fatty acids.– Vitamin deficiency.– Free radicals.

Causes Of ADHD.

UN

DE

RG

RA

DU

AT

E

12

46


Section: 6 of 11



Russell Barkley’s theory of Response Inhibition.– Neuropsychological impairment leads to deficits in:

• Executive Functions.• Self-regulation.• Behavioural or ‘response inhibition’.

• Please Read: Barkley, R. A., (2000). Excerpts from his lecture on ADHD. San Francisco, CA. June 17, 2000. On the Resources Page and on the (2009) Forum.

• Please Review: Barkley, R.A. et. al. (2002). International Consensus Statement (January 2002). Clinical Child and Family Psychology Review, 5(2). p.89-111. On the Resources Page and handed out.

Aetiology And Theories Of ADHD.

UN

DE

RG

RA

DU

AT

E

13

46


Section: 6 of 11




• Self-regulation is:– The ability to inhibit.– The ability to delay.– The ability to separate thought from feeling.– The ability to consider an experience and change

perspective.– The ability to consider alternative responses...

UN

DE

RG

RA

DU

AT

E

14

46


Section: 6 of 11




• Self-regulation is:– The ability to choose a response and act

successfully towards a goal.– The ability to change the response when confronted

with new data.– The ability to negotiate life automatically.– The ability to track cues.

UN

DE

RG

RA

DU

AT

E

15

46


Section: 6 of 11




• Poor self-regulation leads to: – Impulsive behaviour.– Knowing what to do is not the same as doing what

you know.– Cue-less behaviour.– Inconsistent behaviour.– Unpredictable behaviour.– Riding an emotional roller coaster.– Problems with automatic behaviour.

UN

DE

RG

RA

DU

AT

E

16

46


Section: 6 of 11




• Hughes suggests deficits in executive function explain impairment in communication. Verbal rituals & over literal interpretations of language may be due to a failure in inhibitory processes involved in suppressing irrelevant associations. .

UN

DE

RG

RA

DU

AT

E

17

46


Section: 6 of 11




Diet.– Different studies have found metabolic differences in these

children, indicating that an inability to handle certain elements of one's diet might contribute to the development of ADHD-like symptoms.

– Ward (1990) showed that children with ADHD lose zinc when exposed to the food dye tartrazine.

– Certain dietary issues, most commonly a moderate to severe protein deficiency, can cause symptoms consistent with ADHD.

UN

DE

RG

RA

DU

AT

E

18

46


Section: 6 of 11




Diet.– Some studies suggest that a lack of fatty acids,

specifically omega-3 fatty acids can trigger the development of ADHD.

– Children who are breastfed for six or more months seem to be less likely to have ADHD than their bottle-fed counterparts and until very recently, infant formula did not contain any omega-3 fatty acids at all.

UN

DE

RG

RA

DU

AT

E

19

46


Section: 6 of 11




Scepticism Towards ADHD. • Rafalovich (2005).

– Found that many doctors are no more confident in the diagnosis and treatment of ADHD than are many parents.

• Hyper focus.– Most people with ADHD have no difficulties

concentrating when they are doing something that interests them, whether it is educational or entertainment. .

UN

DE

RG

RA

DU

AT

E

20

46


Section: 6 of 11



What Is Autism?

Restricted, repetitive and stereotyped patterns of behaviour.

Impairment in social interaction.

Impairment in verbal and non verbal communication.

UN

DE

RG

RA

DU

AT

E

21

46


Section: 6 of 11



Aetiology And Theories Of Autism.

• Children with Autism display many symptoms that are not specific to Autism.

– Language impairment. – Stereotypic behaviour. – Lower IQ.

• Because of this Happé (1994) argues that it is important for theories of Autism to focus on the features which are specific to autism i.e. the triad of impairment.

UN

DE

RG

RA

DU

AT

E

22

46


Section: 6 of 11




• Genetic/biological factors.– 2-4% rates for siblings.– MZ twins up to 96% concordance.– DZ twins up to 27% concordance.– More common after chromosomal, infections,

traumatic insults to CNS.• One of the hallmarks of Autism is that the

characteristics vary significantly among different children with autism. No two children with Autism are the same.

UN

DE

RG

RA

DU

AT

E

23

46


Section: 6 of 11




• See Rajendran & Mitchell (2007) excellent review. Rajendran, G., & Mitchell, P. (2007). Cognitive Theories of Autism. Developmental Review, 27(2), 224-260.

• Three cognitive theories have dominated psychological research into Autism.– Theory of Mind deficit.

• Social and communication impairments.

– Executive Function deficit.• Stereotyped behaviour and narrow interests.

– Weak Central Coherence.• Local processing rather than global.

UN

DE

RG

RA

DU

AT

E

24

46


Section: 6 of 11



Theory Of Mind Deficit.

Individuals with Autism fail to “impute mental states to themselves and others” (Premack & Woodruff, 1978). – This deficit manifests as inability to ‘mentalise’, or

failure to take into account others’ mental states. – Unexpected transfer test of false belief (Wimmer &

Perner, 1983). – 80 percent of children with Autism fail the

unexpected transfer task and these have a deficit in their theory of mind (Baron-Cohen, Lesile and Frith, 1985).

UN

DE

RG

RA

DU

AT

E

25

46


Section: 6 of 11




• These seminal results have been widely replicated with that task as well as other tests of false belief, such as the Smarties Test ‘Deceptive box’ (Perner, Frith, Leslie & Leekam, 1989).

UN

DE

RG

RA

DU

AT

E

26

46


Section: 6 of 11



UN

DE

RG

RA

DU

AT

E

27

46


Section: 6 of 11



UN

DE

RG

RA

DU

AT

E

28

46


Section: 6 of 11



UN

DE

RG

RA

DU

AT

E

29

46


Section: 6 of 11




• Most children with Autism (and typically developing 3-year-olds) answer like the child in the cartoon.

• This suggests a lack of understanding that people’s actions are based on their own beliefs, even when those beliefs deviate from what the child knows to be true.

UN

DE

RG

RA

DU

AT

E

30

46


Section: 6 of 11




• However, Happé (1994) stated that it was problematical for the theory of mind hypothesis that 20% of Autistic people actually passed tests of false belief. So…

• Baron-Cohen modified his theory by proposing that a theory of mind problem was in fact a delay rather than a deficit.

UN

DE

RG

RA

DU

AT

E

31

46


Section: 6 of 11




• Baron-Cohen (1989) used the more difficult second-order false belief task (I think he thinks she thinks).– 60 percent of the children with Down syndrome.– 90 percent of typically developing children.– but none of the children with autism passed (Mean verbal

mental age of 12.2).• Baron-Cohen concluded that because individuals with Autism

could not pass a second-order task they did not have a fully representational theory of mind. But…

• Bowler (1992) challenged the idea that theory of mind development is delayed in Autism. He found that 73 percent of young adults with Asperger syndrome (AS) passed the second-order false belief task.

UN

DE

RG

RA

DU

AT

E

32

46


Section: 6 of 11




• Most children without Autism show evidence of the development of theory of mind at around 4-5yrs of age.

• ‘Sally Ann’ Study (Leslie et al, 1995) found that autistic children displayed great difficulties in imputing the beliefs of others.

• In historical terms, the theory of mind hypothesis brought developmental psychologists into mainstream Autism research.

• Please read: Frith, U. & Happe, F. (1994) Autism: Beyond Theory of Mind. Cognition, 50, pp.115-132.

UN

DE

RG

RA

DU

AT

E

33

46


Section: 6 of 11



Deficits In Executive Function.

• Executive function – refers to the processes underlying the control of behaviour such as working memory, planning, inhibitory control, and attentional set shifting.

• Suggested that deficits in executive function underlie the cognitive impairments found in Autism (Hughes, Russell & Robbins, 1994; Ozonoff, Pennington & Rogers, 1991).

UN

DE

RG

RA

DU

AT

E

34

46


Section: 6 of 11



Executive Function.

• The disruption of executive processes results in Individuals with Autism displaying difficulties in new or ambiguous situations but no impairment on well learned or routine tasks.

• In the past – associated with frontal lobe neurological damage (Luria, 1966) Damasio & Maurier were first to note similarity of symptoms with Individuals with Autism.

UN

DE

RG

RA

DU

AT

E

35

46


Section: 6 of 11



Evidence For Deficits In Executive Function In Autism.

• Ozonoff, Rogers & Pennington (1991).– Individuals with Autism performed poorly on tests of

executive function despite having passed Theory of Mind tasks.

• Hughes & Russell (1993) argued that online executive control is necessary to pass false belief tasks. Failure on Theory of Mind tasks may be because the demands being made on the capacity of the processes is too great.

UN

DE

RG

RA

DU

AT

E

36

46


Section: 6 of 11



Executive Function.

• Number of studies showing relationship between executive function and Theory of Mind (Perner et al , 1999; Hughes, 1998) but the relationship but the causal direction is unclear.

• Hughes (1998) found performance on Theory of Mind tasks predicted Theory of Mind but Theory of Mind ability did not predict performance on tests of executive function.

UN

DE

RG

RA

DU

AT

E

37

46


Section: 6 of 11



Criticisms Of Executive Function Theory.

• Theory lacks discriminative validity - executive impairments in Autism also appear in a number of other developmental disorders i.e.. ADHD, Tourettes Syndrome and Conduct Disorder.

• Not possible to know if executive impairments are the primary cause of the disorder or appear later and are the consequence of Autism. .

UN

DE

RG

RA

DU

AT

E

38

46


Section: 6 of 11



Weak Central Coherence Theory.• Autism biased toward local rather than global information

processing.

– Inability to experience wholes without full attention to the constituent parts.

– do not succumb to visual illusions (Happé, 1996).

– failure to use context in reading (Happé, 1995).

• Proposes that within the typical cognitive system something exists which enables the processing of incoming information in context for global meaning. This helps us make sense of the world. (Frith,1989; Happé).

• Frith argues that in individuals with Autism, this is disturbed – focus on details at the expense of the whole.

UN

DE

RG

RA

DU

AT

E

39

46


Section: 6 of 11



Weak Central Coherence Theory.

• Explains both the deficits found in Autism and also the strengths exhibited by individuals with Autism.

• Deficit model – different perceptions of the world has implications for social communication and behaviour.

• BUT – the ability to detach from context and process fine detail is an advantage in many visuo-spatial tasks.

UN

DE

RG

RA

DU

AT

E

40

46


Section: 6 of 11



Weak Central Coherence Theory.

• Individuals with Autism have superior performance on the embedded figures test (Shah & Frith, 1983).

• Happé (1998) suggests preference for processing parts rather than wholes is a cognitive style rather than a deficit.

UN

DE

RG

RA

DU

AT

E

41

46


Section: 6 of 11



Weak Central Coherence Theory

• If children with Autism excel at processing stimuli without reference to context this predicts that they would be unable to understand linguistic ambiguities.

• Frith & Snowling (1983, 1986) researched this by looking at reading performance and at the ability to pronounce homographs in context.

• They predicted that autistic children would only show reading failure when it was necessary for them to take context into account.

UN

DE

RG

RA

DU

AT

E

42

46


Section: 6 of 11



Weak Central Coherence.

• Kate Plaisted (2001) points out that a number of studies show that individuals with Autism are able to selectively attend to either the global or the local level of processing when directed to do so.

• But in a task of divided attention they displayed a preference to process at local level (Plaisted, 1999).

• She suggests that individuals with Autism have difficulty making sense of the world because of an impaired ability to process the similar features between stimuli or situations. This hinders the transfer of learning from one situation to another.

UN

DE

RG

RA

DU

AT

E

43

46


Section: 6 of 11



Weak Central Coherence.

• Plaisted’s theory offers an explanation for the poor ability to generalise learning often observed in individuals with Autism (Ozonoff & Millar, 1995).

• Also explains superior performance on tasks such as the embedded figures task and block design where the ability to process unique features well coupled with the poor processing of similar features is an advantage.

UN

DE

RG

RA

DU

AT

E

44

46


Section: 6 of 11



Systemizing-Empathizing / The Extreme Male Brain

• Systemizing is the drive to analyse or construct a system. The rules or the laws that govern that system in order to predict how it will behave. Baron-Cohen

• Empathizing is completely different. It’s about being able to imagine what someone else is thinking or feeling, and having an emotional response to the other person’s feelings.

• Males have a stronger drive to systemize and females have a stronger drive to empathize.

• People on the Autistic spectrum show an exaggeration of the male profile – an extreme ‘male’ brain.

• TOM is part of empathy .

UN

DE

RG

RA

DU

AT

E

45

46


Section: 6 of 11



“Trendy” Theories of Autism.

• Vaccines, MMR.• Allergies.• Gut/Intestine problems problems.• Food intolerance.• Environmental toxins.• Refrigerator Mothers.• Poor Parenting.• Vitamin Deficiency.

UN

DE

RG

RA

DU

AT

E

46

46


Section: 6 of 11



Summary.

• Causes of ADHD and Autism are varied and speculative. Although recently genetic research has provided the best potential for understanding the underlying aetiology.

• ADHD.– Response Inhibition.– Diet/nutrition/intolerance.

• Autism.– Theory of Mind deficit.– Executive Function deficit.– Weak Central Coherence.– Systemizing-Empathizing / Extreme Male Brain

• Other ‘Trendy’ Theories for both.– Take your pick…

• Autism/ADHD: No single cause; no single cure.

section 6 - aetiology of adhd & autism

Education