Brain Differences in Autism and Aspergers

Brain Differences in Autism and Aspergers

Brain Differences in Autism and Aspergers

Autism and Asperger's are two of the disorders that make up the umbrella of the autistic spectrum disorders. These disorders are characterized by early deficits in social and communication skills. These disorders are included in the definition of Pervasive Developmental Disorders in the DSM IV-TR. Although they are categorized under the same heading, they are comprised of distinct features and symptoms that make each unique to the other.

The signs of autism typically begin before the age of three, although if the signs are missed, diagnosis typically occurs at a later age. The critical warning signs are the lack of verbal skills in the child or the avoidance of interacting with children of their age group. Eigsti and Shapiro (2003) defined the main areas affected by Autism: Social Reciprocity, Language and Communication, Repetitive Behaviors and Stereotyped Interests and Cognitive Impairments. Parents often fear that their child is deaf due to the lack of communication. Upon testing, the child's hearing is determined to be normal. The child's perception and processing of sensory information is also affected by autism. There are varying degrees of severity and each child must be assessed on an individual basis. Recent studies indicate a prevalence for autism of 5.2 per 10,000, with 80% of affected individuals exhibiting MR; prevalence rates increase to 16-19 per 10,000 when all disorders on the spectrum are included (Fombonne, 1999).

Aspergers disorder differs slightly from the diagnosis of autism. Although both share the classic symptoms of difficulty with communication, social interaction and repetitive stereotyped behavior, their presentation varies slightly. Individuals with Aspergers Syndrome tend to have normal, if not above average intelligence. They struggle with social conventions and have difficulty understanding appropriate behaviors and responses. Khouzam (2004) stated, "As a result, they often seem tactless or rude, and making friends can be hard for them...they may be unable to take hints, keep secrets or understand metaphor, irony and humor. The meaning of gestures, tone of voice, and facial expressions are a mystery to them, and their own body language and expressions may be inappropriate or hard to interpret". Individuals with Aspergers tend to be extremely set on routine and become very upset when that is disrupted. Asperger's disorder was added to the American Psychiatric Association's official diagnostic manual in 1994 and is now believed to affect about one in 300 children (and adults), nearly 90% of them male. Carter (1998) stated, "Four times more males than females suffer from autism and nine times more from Asperger's syndrome."

Are these disorders more prevalent in males? And if so, is there a biological basis behind this affliction? Carter (1998) discussed the fetal testosterone model that emphasizes the increased likelihood of males being afflicted with autism or aspergers syndrome. Because testosterone has a strong impact on fetal brain development, the right hemisphere on male infants has been found to be thicker than that of females. Females have a larger corpus collosum, which may explain their advanced verbal fluency over that of males (Carter, 1998). This may explain why autism affects males more than females and why the verbal capacities in these males with autism are much more affected than with females.

Autism and Aspergers Disorders have been found to have strong genetic roots. Jorde et al (1990) found that autism clusters in families and family studies demonstrate an increased risk of autism in first-degree relatives of affected individuals. Studies have also demonstrated increased rates of sub-clinical autistic symptomatology such as an increase of 15-20% in cognitive impairments in siblings of probands, and of 20% for the broader phenotype in siblings. The biological basis for the development of these disorders has strong roots in twin studies and family characteristics. Carter (1998) stated, "Autism is strongly heritable and one of the genes that is suspected to be involved lies in a section of chromosome that is also thought to harbour a gene strongly implicated in the development of language." There is ongoing research targeted at pinpointing these specific genes to determine the exact causes of these disorders.

Scientists are studying several areas of the brain in order to identify the exact structures responsible for the development of these disorders. A concept known as Theory of Mind has been shown to be lacking in individuals with autism and aspergers syndromes. "The instinctive ability to know what is in another person's mind is known as 'theory of mind'" (Carter, 1998). This is a lack in the individual with autism to understand that others have their own thoughts, plans, ideas and points of view. This also comprises their difficulty with understanding the emotions and attitudes of others. Individuals with autism have difficulty understanding when others don't know something, leading to increased frustration and irritability at the lack of communication. This may appear extremely egocentric, although there is no indication that individuals with autism possess these thoughts or feel superior to others in any way.

Theory of mind tests have been used in individuals with autism in order to identify areas of the brain in which difficulty in understanding appears to occur. These tests sought to examine the individuals' ability to reflect on the viewpoints of others and to comprehend the concept that others have differing thoughts in similar situations. Nieminen-von Wendt et al (2003) found there was an increased activation in the occipitotemperal areas and in the thalamus during Theory of Mind stories as compared to control stories in both controls and subjects with autism. The activation during the Theory of Mind stories was more extensive and more intensive in the left medial frontal area and in the anterior cingulated area in the controls than in the subjects with Autism. These findings correlated with previous results that high emotional loading of visual stimuli increased the activation of visual association areas including also the occipitotemporal area (Reiman et al, 1997).

Various stories were given to a group of normal participants and individuals diagnosed with aspergers syndrome. The purpose of these was to examine which areas of the brain were affected during the reading and processing of these stories. Carter (1998) stated that a