Autism and the Brain

The amygdala is a small, almond-shaped structure in the limbic system of our brain, known for its key function in the cascade of events associated with detecting threat. When the thalamus communicates sensory information to the amygdala, it, in turn, initiates the sympathetic nervous system’s fight/flight response.

The amygdala is located in the medial temporal lobe and contains three nuclei: the laterobasal, the centromedial, and the superficial nucleus. Each is associated with unique patterns of connectivity with different brain regions, including the prefrontal cortex, hippocampus, and insula, amongst others (Bzdok et al., 2012).

Through its connection with the hippocampus, the amygdala encodes threatening contingencies into our memory to help us avoid future threats (LeDoux, 1996). The various parts of the amygdala stimulate, what Carter (1998) referred to as various survival strategies, mainly fight, flight, and appeasement.

How is the amygdala relevant to autism? Autism is popularly perceived as a genetic condition that impacts the functioning of various brain mechanisms that influence the social-emotional processing of information and behavior (Yin & Schaaf, 2017).

In 2000, Baron-Cohen et al. proposed the amygdala theory of autism, stating that autistic individuals necessarily differ in the functioning of their amygdala. He proposed that the amygdala of autistic individuals shows reduced activation in response to interpreting images of individuals' eyes from photographs.

Since his theory was presented, researchers did not find a consistent association between the activation strength of the amygdala and comprehension of emotional expressions and nonverbal social cues in autistic individuals (Birmingham et al., 2011). A decade later, Birmingham (2011) concluded that “social disturbances in ASD would be better understood in terms of disruption of the complex network of structures with which the amygdala is connected rather than in the amygdala itself.”

Within the last two decades, our understanding of the amygdala has greatly expanded beyond the focus on just its role in the activation of the fight/flight response. Current theories suggest that the amygdala not only detects threats in the environment, but also responds to “a broader range of self-relevant information” including aversive and pleasurable physiological and psychological states within the organism and encompassing social and physical environments (Sander et al., 2003).

The relevance detection theory of autism suggests that the mechanism underlying the social-emotional communication differences in autistic individuals is “disruption of the neural system devoted to the processing of self-relevant information, primarily relying on the functional and connectivity integrity of the fronto-amygdala circuit” (Zala and Sperduti, 2013).

Sander et al. (2003) defined relevant stimulus as what “influences (positively or negatively) the attainment of... goals, the satisfaction of... needs, the maintenance of... well-being within the physical environment and the social context (Sander et al., 2003).

The amygdala relevance detection theory helps to appreciate that non-autistic and autistic individuals may focus their attention on unique aspects of their inner experience and environment, neurotypical individuals more so in reference to the bigger picture or main idea, and neurodivergent individuals with a unique focus on other aspects of the situation or their inner experience.

In support of this theory, Harris et al. (1987) suggested that autistic children find it difficult to reflectively appraise their inner experiences or comprehend them in a way that takes into account a “bigger picture” of a situation, or distinguish between their emotional experiences.

The amygdala relevance detection theory offers yet another neurological perspective that helps us to appreciate that individuals focus their attention on aspects of their inner experience and environment in unique ways, affecting their processing of emotional states, perspective taking, and interpreting of social cues; helping to build bridges of mutual understanding and dialogue.