Brain Response to Serotonergic Medications in ASD

Inclusion Criteria: * Intelligence Quotient (IQ) above 70 * Has capacity and is capable of giving written informed consent * Able to read, comprehend and record information written in English * Bodyweight of \<120 kg and BMI within the range 18.5 - 33 kg/m2 (inclusive). * Not taking medication directly affecting gamma-aminobutyric acid (GABA) neurotransmission for at least the past 4 weeks * Not taking medication directly affecting the serotonergic system for at least the past 4 weeks * ASD only: Diagnosis of Autism Spectrum Disorder (ICD 10-R criteria, confirmed using the Autism Diagnostic Interview (ADI) and/or ADOS) including atypical autism * ASD only: Being recommended drug therapy for symptoms of depression and/or anxiety * Controls only: No diagnosis of Autism Spectrum Disorder (ICD 10-R criteria, confirmed using the ADI and/or ADOS) * Controls only: No diagnosis of major depressive disorder according to the Diagnostic and Statistical Manual of Mental Disorders (DSM) IV or ICD 10. Exclusion Criteria: * Current risk of self-harm * Acute risk of suicidality (e.g., current suicidal ideations) * Age \< 18 years or \> 60 years old. * Taking medication directly affecting the serotonergic system (e.g. SSRIs, Tricyclic antidepressants) * Taking medication directly affecting GABA neurotransmission (e.g. antiepileptic drugs, and benzodiazepines) * Taking antipsychotic medication or medication for attention deficit hyperactivity disorder (ADHD) for the past 4 weeks * History of dependence to alcohol or substances of abuse (excluding nicotine) * Major mental illness (e.g. psychosis), or a learning disability (mental retardation) * Needle phobia * Medical/genetic disorder associated with ASD * Diagnosed and treated for hyperkinesis or Tourette's syndrome * Allergy to food colouring