Autism Part 2

So, what causes autism? The person who answers that question wins the Nobel Prize in Medicine! Unfortunately, my best guess is that there will not be an answer, but multiple answers since there is no autism, but multiple autism spectrum disorders each of which may have its own unique etiology (cause) and biological features.

The research on the causes of autism appears to bear out this hypothesis. In an article, entitled “Neuropathological Findings in Autism”, (Brain 2004 127(12):2572-2583; doi:10.1093/brain/awh287), that extensively reviewed the research on autism spectrum disorders Saskia J. M. C. Palmen, Herman van Engeland, Patrick R. Hof and Christoph Schmitz conclude that “the majority of the neuropathological data (on autism) remain equivocal” with studies variously relating autism spectrum disorders to: (a) a decrease in the number of Purkinje cells throughout the cerebellar hemispheres without significant gliosis, (b) features of cortical dysgenesis, (c) increased cell packing density of smaller neurons in the limbic system, (d) age-related abnormalities in the cerebellar nuclei and the inferior olive, (e) abnormalities in nicotinic and muscarinic cholinergic neurotransmitters/neurons and (f) abnormalities in the GABAergic system.

While neuroimaging and neuropathology studies have yielded equivocal (and occasionally polar opposite) findings, several functional features of autism spectrum disorders remain constant and implicate involvement of several brain functions.

• Studies have consistently demonstrated abnormal fear (ie., “fight or flight”) responses among individuals with autism spectrum disorders with references to social anxiety, poor eye contact (avoidance), sleep disturbances, obsessive-compulsive features, anger, poor impulse control, depression and paranoia… and these abnormalities in behavior coincide with research showing abnormalities in the size and function of the amygdale which is a relatively small almond-shaped region embedded within the limbic system, the same limbic system that govern “fight or flight” distress responses. This brain (amygdala) – behavior (fight or flight) connection appears to account for a cluster of symptoms/problems associated with autism spectrum disorders. Unfortunately, the cause of amygaloid abnormalities is not clear. While it is possible that the amygdaloid abnormalities reflect a breakdown in the blueprint (genetic/DNA), it remains quite possible that this abnormality is related to a breakdown in other brain regions connected to the amygdala (ie., other regions whose input to the amygdala spurs development). The possible role of a breakdown of the myelinated axons that connect brain regions (ie., limbic-frontal lobe connections) has been suggested.
  
• Research has consistently demonstrated the presence of abnormal sensory gating (ie. inhibition, selection, direction, etc.) among individuals with autism spectrum disorders with references to no pain responses, exaggerated pain responses, needs for deep pressure/touch, avoidance of touch, ear guarding under high stimulation settings, limited visual searches, … and these abnormalities in behavior coincide with research showing abnormalities in the size and function of the thalamus. The thalamus is located deep within the subcortical region and has been described as being the Grand Central Station of the brain with a primary function of routing sensory information (ala passengers) to their appropriate locations. Poor routing may account for sensory over-load along with failure to attend to some relevant stimuli… along with the bizarre symptoms of sensory contamination (see Born on a Blue Day in which the author reports seeing numbers in color). This brain (thalamus) – behavior (sensory routing) connection appears to account for a cluster of symptoms/problems associated with autism spectrum disorders. Unfortunately (does this sound familiar… see the amygdala above) the cause of thalamic abnormalities is not clear. While it is possible that the thalamic abnormalities reflect a breakdown in the blueprint (genetic/DNA), it remains quite possible that this abnormality is related to a breakdown in other brain regions connected to the thalamus (ie., other regions whose input to the thalamus spurs development). The possible role of a breakdown of the myelinated axons that connect brain regions (ie., cortico-thalamic and upper brainstem-thalamic connections) has been suggested.
  
• Research has consistently demonstrated the presence of abnormal social responses among individuals with autism spectrum disorders with references to poor eye contact, limited initiation of reciprocal play, limited attachment/empathy, failure to follow the gaze of others and failures to maintain social relationships… and these abnormalities in behavior coincide with research showing abnormal “mirror neuron” activity. “Mirror neurons” have been named due to the fact that the neurons appear to be activated when an animal performs an action and when the animal observes the same action performed by another animal. These “mirror” neurons have been implicated in observational or social learning, social interest and language development. “Mirror neurons” have been identified within the prefrontal cortex….and the “frontal lobes” tend to function as our executive or coach with functions of organization, planning, use of feedback to adapt/change, observer functions and internalization of social rules. This brain (frontal) – behavior (poor executive function) connection appears to account for a cluster of symptoms/problems associated with autism spectrum disorders… including disorganization (ie., lining up is not organization), poor planning (ie., inability to utilize the future for present decision-making), failure to use feedback (ie., perseverative responses), poor observer functions (ie., difficulties seeing the world through the eyes of others) and deficient internalization of social rules (particularly unwritten rules). Unfortunately (does this sound familiar… are you getting the picture?) the cause of frontal abnormalities is not clear. While it is possible that the frontal abnormalities reflect a breakdown in the blueprint (genetic/DNA), it remains quite possible that this abnormality is related to a breakdown in the myelinated axons that connect the frontal lobe to other brain regions.

So, what causes autism? We do not know but several lines of evidence appear to implicate a disruption in the development of the myelinated axons that connect various brain regions and that there may be a multitude of etiologies or causes that result in this final common pathway and then again, maybe there are simply a variety of etiologies and that our decision to group these disorders into a single category reflects our tunnel vision or narrow view. But the bigger question is…. WHAT DO WE DO? Hmmmm… maybe another time we can start that.

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Dr. Richard Dowell is a Neuropsychologist located in Pennsylvania. Dr. Dowell evaluates upwards of 400 children and adolescents each year. In addition, Dr. Dowell is recognized as one of the top Forensic Neuropsychological witnesses in the North East.

Dr. Dowell can be contacted at DrDowell@NeuropsychologicalServices.net

For more information on Neuropsychology visit NeuropsychologicalServices.net