Neuroanatomical-behavioral correlates in autism: A working hypothesis

Abstract

This chapter correlates emotions and attachment behavior in autism with the disturbed neuroanatomy found in the brains of these individuals. Neuropathological postmortem studies have consistently found abnormalities in the limbic system and the cerebellum of autistic individuals. Abnormal limbic structures include the amygdala, hippocampus, septal nucleus and anterior cingulate cortex. In the cerebellum, abnormalities have been found in the cerebellar hemispheres and in the fastigial, emboliform and globose nuclei. Autistic individuals fail to activate the amygdala when required to interpret emotions in facial expressions. A normal amygdala is able to discern subtle social-emotional nuances and attach emotional significance to sensory input, something which appears to be deficient in persons with autism. Abnormal processing of fear by the amygdala during development may result in failure of autistic individuals to detect and avoid danger. Normal septal nuclei, together with the anterior cingulate cortex, act to promote selective attachments to other humans. Autistic children show deficient attachment behavior and early failure of person-specific bonding. The anterior cingulate cortex is involved in processing and modulating the expression of emotional nuances, which appears deficient in autistic individuals. It is capable of producing emotional sounds and the separation cry, in an attempt to seek comfort. The hippocampus, in concert with the medial hypothalamus and septal nuclei, prevents extremes in arousal and maintains quiet alertness. In addition, it has strong interactions with the amygdala in storing emotional reactions to events and recalling personal emotional memories, functions that appear to be impaired in autism. Cerebellar abnormalities may result in disturbances in a neural network involved in the motivation and organization of emotion. Abnormalities in the cerebellar nuclei may play a role in the affective disturbance, abnormal language development and inappropriate social and psychological behaviors in autism. Development of limbic structures in normal infants, during the first year of life, follows a pattern that correlates with the development of attachment behavior. The amygdala becomes functional early in life, promoting indiscriminate attachments. The septal nucleus and anterior cingulate cortex functionally develop in the second half of the first year of life and correlate with specific attachments and fear of strangers. These developmental patterns appear disturbed in autistic infants. The study of psychological-neuroanatomical correlates of autism can provide a new understanding of this perplexing disorder.