Brain studies have shown many differences between neurotypical people and people on the autism spectrum. Not everyone with autism has all of these features. And not all studies show the same thing. Published findings include
- Larger brain size especially when younger
- Differences in the size of various brain regions
- Different (often lower than in neurotypical) coordination (or connectivity, or coherence) across brain regions
- Different concentrations of brain chemicals
- Innate immune activation (sometimes called neuroinflammation)
- Different ways of processing information
- Differences in electrical activities at the neuronal level (e.g., synapses)
- Differences in oscillatory activity and oscillatory networks
- Differences in blood flow
- Different relationships between parts of the right and left hemispheres
HOW MIGHT THESE BRAIN DIFFERENCES CAUSE OR CONTRIBUTE TO AUTISM?
We don’t really know but here are some of the theories:
Psychological and neurofunctional-oriented models
- Version 1: Disturbance of particular parts of the brain that govern specific brain functions
- (examples: amygdala (related to emotions and fear in particular), cerebellum (coordination of processes including movement and thinking), fusiform face area (face recognition), anterior cingulate (autonomic or stress system, thinking and feeling), basal ganglia (movement and impulse regulation)
- Version 2: Disturbance of brain networks so that cells and/or regions of the brain communicate differently with each other than in neurotypical people
- Theory of “underconnectivity” and subsequent variations
Neurobiology-oriented models
- Version 3: Disturbance of brain chemistry, particularly neurotransmitters so that chemical signaling works differently
- Neurotransmitters with differences documented include serotonin, acetylcholine, dopamine
- Version 4: Increase in the ratio “excitation” and not enough “inhibition” in the brain which can cause pervasive changes since a properly regulated “excitation/inhibition ratio” is fundamental to brain function
Pathophysiology-oriented models
- Version 5a: Disturbance of physical properties of the brain, such as cellular chemistry, blood perfusion, cellular energy production or inflammation so that cells act differently with each other and in their regions and networks
- Version 5b: Parameters governing oscillatory activities and synchronization are altered by a vast array of simultaneous and often interrelated perturbations of tissue pathophysiology
WHAT MIGHT LEAD TO THESE BRAIN DIFFERENCES?
That is, if brain differences “cause” autism, what “causes” these brain differences?
- Genes
- Environment
- Physiology
INTERACTIONS BETWEEN PHYSICAL CHANGES AND CHANGES IN ACTIVITY AND FUNCTION
- Brain development is impacted by physical factors
- Brain development is also impacted by experience: Early experience creates “circuitry” changes that have long-range impacts
