The amygdala theory There is a growing body of tentative evidence indicating the
amygdala's involvement in the development of autism. The focuses on the importance of the amygdala in relation to social functioning and observes that autism is largely a severe impairment of social functioning. The amygdala is thought to be associated with the
fight-or-flight response in animals and its activity is heavily correlated with fear in humans. Additionally, it has been heavily implicated in relation to social functioning in various animal studies. Evidence suggests an amygdala hyperactivity model may be more accurate than one comparing it to a
lesion. Lesion studies have shown that amygdala damage results in severe social impairment among animal models. Vervet monkey mothers with amygdala lesions were shown to be much less caring with their young, neglecting and even abusing them. Rats with amygdala ablations become much more docile. is critical in the involvement of processing mental state and emotional information from complex visual stimuli, particularly the eye region. However, individuals with autism do not seem to engage the amygdala during tasks when processing the emotions of others. Instead, they exhibit greater reliance on temporal lobe structures, specialized for verbally labeling complex visual stimuli and processing faces and eyes. This shift in processing may serve as compensation for potential amygdala abnormalities in individuals with autism. Studies conducted specifically on nonspeaking autistic individuals provide similar evidence. Brain studies have shown several amygdaloid impairments among those with ASD. The amygdala in those with nonspeaking autism have less volume compared to controls, contain a higher density of neurons suggesting hyperconnection, and show a negative correlation between amygdala size and impairment severity among subjects. While infantile autism is actually associated with an oversized
amygdala, there are developmental theories as to how this may occur. Research on
major depressive disorder has shown that excessive activation such as stress or fear leads to
allostasis, or degeneration of the neurons involved in creating the phenomenon. Initial hypertrophy results in
atrophy and reduction of brain size in the given region. Over time, this occurs in patients with severe depression, and they develop a decreased amygdala size. Some scientists theorize that this is happening early during infancy in the autistic brain, accounting for the initial overgrowth and later observed size reduction. When
eye tracking software is employed to record where subjects focus their visual attention on images of human faces, small amygdala volume is associated with decreased
eye fixation. Eyes are considered to be especially important for establishing human connection and conveying emotion, thus fixation on them is considered to be a crucial part of identifying people and emotions in a social setting. In addition to a negative correlation to eye fixation studies showed a smaller amygdala was associated with impairment in
nonverbal communication skills as well. This suggests that the amygdala is critical in developing all types of communicative abilities, not just verbal. This suggests the amygdala may play a crucial role in relating to other humans in a way that allows for behavioral mimicry. Among nonspeaking autistic patients, researchers could predict symptom severity based on amygdala activity. Those with the least amygdala activity had the most impaired nonspeaking communication abilities, those with the most activity had the strongest communication abilities. The development of language, similar to the development of most physical skills, relies heavily on mimicry of other humans. ASDs are known to impair one's ability to focus on and relate with people possibly as a result of a damaged amygdala. Nonspeaking autistics will often be able to learn more basic communicative skills such as pointing to objects or selecting a picture from a list. These skills are far more simple and do not require the degree of personal connection needed for language development. ==Language outcomes==