Autism spectrum disorder (ASD) is a developmental disorder that affects social behavior and communication. The symptoms are generally identified during the first two years of life.¹ The Mayo Clinic² describes common signs of ASD as the resistance of cuddling, performing activities that lead to self-harm and difficulty in social interactions. As of yet, there is no identified cause of ASD. However, a specialized type of neuron, called von economo neurons (VENs) could hold the answers to an ASD individuals’ lack of social intuition, response to rewards and social bonding, partially explaining a neurobiological cause for the social behaviors of individuals with ASD. An article published in Trends in Cognitive Science, identifies three receptor types on the VENs whose chemical signal, when activated, could lead to feelings of intuition, social bonding and social reward. The authors dive further to link the lack of the VENs in the brain area related to cognitive and emotional processing, called the anterior cingulate cortex (ACC) to ASD.^3,4

The three receptors types on the VENs are vasopressin 1a (V1a), dopamine 3 (D3) and serotonin 2b (5-HT2b). Genetic variations of the gene that codes for the V1a receptor has been linked to activation of the emotional center of the brain specifically during emotional processing of facial expression.⁵ D3 receptors have been previously linked to cognition. Cognition is responsible for many mental processes, such as attention, memory and comprehension, which make it vital for understanding, adaptation and applying knowledge to given situations.⁶ The D3 receptor has also been thought to signal when rewards are to be expected in uncertain circumstances.³ The 5-HT2b receptors are highly expressed on the VENs but rarely in other areas of the brain.³ However, the VENs are found in relatively large proportions in the human stomach and intestines.³ Other research has implicated 5-HT2b receptors as modulators of dopamine neurons possibly signaling punishment. Further, mice lacking the 5-HT2b receptors behave similarly to mice addicted to cocaine, where cocaine addiction increases the levels of dopamine in several brain areas.^3,7 Therefore, the D3 receptors signal reward and the 5-HT2b receptors could oppose those signals and create balance between reward and punishment.³ Together these three receptors and their signaling allow us to read others’ emotions and connect, expect rewards and have gut feelings when something is wrong (Figure 1).

This study first compared the total VEN number in apes and newborn, child and adult humans. Immunocytochemistry is a technique used to identify proteins; used here to visualize the V1a, 5- HT2b and D3 receptors on the VENs in the ACC of humans.⁸ They found that VENs are concentrated in the right hemisphere and only 15% of total VENs are present at birth and increase until 4 years old. To link the VENs to ASD, the axon fibers that carry information were observed and showed the neuronal connections are disorganized in ASD individuals, which could be due to an abnormal growth pattern during development. Individuals with ASD also showed a relatively lower number of the VENs in the ACC.

The authors concluded that the VENs in those with ASD fail to develop properly which is partially responsible for the lack of intuition, social bonding and response to rewards due to the lack of receptors associated with these complex functions. Further research to manipulate number and connections to find a causal relationship between VENs and their associated receptors to the social behaviors would be more convincing in linking these things directly to ASD to truly be considered a partial cause.

[+] References

[+] Other Work By Janee Meengs