1. impairment in social interaction and communication
2. repetitive or obsessive behaviors
3. preoccupation with particular subjects or interests
4. good (sometimes superior) grammar and vocabulary
5. normal cognitive development
6. normal or above average intelligence.

Although the behavioral symptoms of Asperger's syndrome are well established, very little is known about the disorder's neurobiological roots. Some studies have shown that people diagnosed with autism have abnormalities in the frontal and parietal lobes of their brains. Dr. Declan G. M. Murphy and a team of researchers at St. George's Hospital Medical School in London searched for similar cortical abnormalities in people diagnosed with Asperger's syndrome. They also correlated these differences with the severity of the Asperger's symptoms.

The researchers used a technique called proton magnetic resonance spectroscopy (or "¹H-MRS", because "¹H" is the chemical symbol for a proton). This method measures the brain's concentration of metabolites ("break down products") involved in energy production. Measuring metabolite concentration gives researchers an overall picture of the state of the neurons in a particular brain area. According to Dr. Murphy, metabolite concentrations measured by ¹H-MRS give "an integrated look at how many neurons you have, if they are insulated okay, and if they are functioning metabolically." So abnormalities in metabolite concentrations can indicate many different kinds of neuronal abnormalities. Some autistic patients have abnormal metabolite concentrations in certain brain areas. Until Dr. Murphy's study, no one had used ¹H-MRS to look for abnormalities in Asperger's patients.

Dr. Murphy and his colleagues studied 14 people with Asperger's syndrome and 18 control subjects. In all subjects, metabolite concentrations were measured in the frontal and parietal lobes. Also, all subjects took two different tests:

• Yale-Brown Obsessive Compulsive Scale: measures the obsessive or repetitive behaviors often seen in Asperger's patients
• Autism Diagnostic Interview: measures the severity of many different autistic traits.

The researchers found that Asperger's subjects had a significantly higher prefrontal lobe concentrations of all metabolites measured. Also, the concentration of one of the metabolites (N-acetylaspartate) was positively correlated with obsessive behavior. The concentration of another metabolite (choline) was positively correlated with social impairment. In other words, the higher the concentration of these chemicals in the subject's prefrontal lobe, the more likely the person was to have a high score on the Yale-Brown or Autism Diagnostic tests. People with highly abnormal prefrontal metabolite concentrations were likely to have highly severe Asperger's symptoms. No differences were found in metabolite concentrations in the parietal lobe.

The authors conclude that Asperger's subjects have neuronal abnormalities in the prefrontal lobe and that these abnormalities are related to the clinical severity of their symptoms. It is not known how these prefrontal neurons are abnormal or how the abnormalities relate to the severity of such symptoms as obsessive behaviors and social difficulties. Future experiments must be performed to answer these remaining questions.