Some research has reported an overall brain enlargement in autism, while others suggest abnormalities in several areas of the brain, including the frontal lobe, the mirror neuron system, the limbic system, the temporal lobe, and the corpus callosum.In functional neuroimaging studies, when performing theory of mind and facial emotion response tasks, the median person on the autism spectrum exhibits less activation in the primary and secondary somatosensory cortices of the brain than the median member of a properly sampled control population. This finding coincides with reports demonstrating abnormal patterns of cortical thickness and grey matter volume in those regions of autistic peoples brains. Brain connectivity
Brains of autistic individuals have been observed to have abnormal connectivity and the degree of these abnormalities directly correlates with the severity of autism. Following are some observed abnormal connectivity patterns in autistic individuals:
Decreased connectivity between different specialized regions of the brain (e.g. lower neuron density in corpus callosum) and relative over-connectivity within specialized regions of the brain by adulthood. Connectivity between different regions of the brain (long-range connectivity) is important for integration and global processing of information and comparing incoming sensory information with the existing model of the world within the brain. Connections within each specialized regions (short-range connections) are important for processing individual details and modifying the existing model of the world within the brain to more closely reflect incoming sensory information.
No response to name (or gazing with direct eye contact) by 6 months. No babbling by 12 months. No gesturing (pointing, waving, etc.) by 12 months. No single words by 16 months. No two-word (spontaneous, not just echolalic) phrases by 24 months. Loss of any language or social skills, at any age.The Japanese practice is to screen all children for ASD at 18 and 24 months, using autism-specific formal screening tests. In contrast, in the UK, children whose families or doctors recognize possible signs of autism are screened. It is not known which approach is more effective. The UK National Screening Committee does not recommend universal ASD screening in young children. Their main concerns includes higher chances of misdiagnosis at younger ages and lack of evidence of effectiveness of early interventions There is no consensus between professional and expert bodies in the US on screening for autism in children younger than 3 years.Screening tools include the Modified Checklist for Autism in Toddlers (M-CHAT), the Early Screening of Autistic Traits Questionnaire, and the First Year Inventory; initial data on M-CHAT and its predecessor, the Checklist for Autism in Toddlers (CHAT), on children aged 18–30 months suggests that it is best used in a clinical setting and that it has low sensitivity (many false-negatives) but good specificity (few false-positives). It may be more accurate to precede these tests with a broadband screener that does not distinguish ASD from other developmental disorders.