Autism

Presented by : Hosein Hamdi

• Autism manifests during the first three years of life

• Genetic factors play a significant and complex role in autism

• Social skill impairments

• Verbal and nonverbal communication deficiencies

• Restricted and repetitive patterns of behavior, interests, and activities

• Imitation skill deficiencies

• Uneven cognitive skills including a concrete learning style with impaired abstract thought

• Variable levels of cognitive ability from mentally retarded to normal or above average

Some Key Symptoms of Autism

• Diminished emotional reactivity to many (particularly socially salient) stimuli

• Strong negative emotional reactivity to some lower-order stimuli or to variations in routine

• Impaired joint attention and difficulties in flexibly disengaging and shifting attention

• Deficient adaptive timing of motor behaviors

• Subtle abnormalities during first year becoming more dramatic during years two and three

• Abnormalities in neocortical, hippocampal, limbic, and cerebellar regions of the brain

The main question

What brain mechanisms underlie autism and howdo they give rise to autistic behavioral symptoms ?

To understand how these brain dysfunctions result in

the behavioral and cognitive manifestations of autism

requires, first, neural models of the normal behavioral

functions that break down during autism

The first model ART (Adaptive Resonance Theory)

• ART proposes how the brain learns to recognize objects and events

• ART predicts that all conscious events are resonant events

• Resonance occurs when bottom-up perceptually-driven inputs and learned top-down expectations are matched.

• The top-down expectations can prime the brain to anticipate expected feature patterns

• The degree of match that is required for resonance and sustained attention to occur is set by a vigilance parameter

• Low vigilance allows the learning of broad abstract recognition categories

• High vigilance forces the learning of specific concrete categories

• If a match is inadequate, then the current input is processed as a novel stimulus. Attention is then rapidly reset so that memory can be searched for another, or new, representation of the event

The ART Model

Conclusion

ART model proposes that individuals with autism have their vigilance fixed at such a high setting that their learned representations are very Concrete

The second model CogEM (or Cognitive-Emotional-Motor)

• Associates external objects and events in the world to internal feelings and emotions that give these objects and events value

• These emotions also activate the motivational pathways that energize actions aimed at acquiring or manipulating objects or events to satisfy them

• The resonance between sensory and emotional representations tends to focus attention selectively upon objects and events that promise to satisfy emotional needs

DRIVE

PREFRONTAL CORTEX

External world

Internal drive input Autonomic & Endocrine outputto target organs

Motor Commands

SENSORY

PrefrontalCortex

PrefrontalCortex

The Inverted-U law

• If the emotional center is overaroused, then the threshold toactivate an emotion is abnormally low, but the intensity of emotion is abnormally small

• In contrast, if the emotional circuits are underaroused, then the threshold for activating an emotion is abnormally high but, when this threshold is exceeded, the emotional response can be hyperreactive

Imaging studies have identified gross anatomical abnormalities in the limbic systems and emotionalcenters of autistic individuals so they experienceunderaroused emotional depression

a) Normal

b) Underaroused depression

Summary

This article describes neural models which proposes how cognitive and

emotional processes that involve brain regions may interact together to create

and perpetuate autistic symptoms. These model processes were originally

developed to explain data concerning how the brain controls normal behaviors

and shows how autistic behavioral symptoms may arise from prescribed

breakdowns in these brain processes, notably a combination of underaroused

emotional depression in the amygdala and learning of hyperspecific

recognition categories in prefrontal cortices.

Reference

Grossberg S, Seidman D. Neural dynamics of autistic behaviors : Cognitive, emotional, and timing substrates. Psychological Review 2006;113:483–525.