Focus on the Limbic System
To understand a brain disorder it is first necessary to determine which brain areas are affected. Only then can one address whether these changes are consistent with the observed behavioral changes. This chapter considers structural and imaging studies on the autistic brain. For the most part, the neurological data reviewed here span the period of changes in prevalence, and caution is needed in extrapolating from historic ASD to the new phase of increasing prevalence.
The human brain is a large and exceptionally complicated organ, impossible to cover properly here. For structural details the interested reader is referred in the first instance to illustrative internet conceptualizations such as [Build a Brain,]1 to databases including the [Digital Anatomist Information System]2 and the Whole Brain Atlas,3 and to a general comprehensive textbook.4 However, in the context of autism and autistic spectrum disorders it will be important to distinguish the major regions of the brain (see Figure 5.1).
The cerebrum or cerebral cortex is the largest part of the human brain. The surface is highly convoluted with many deep fissures: dividing the mass of the brain on each side into four lobes – the frontal, parietal (the outer wall), occipital (the back), and temporal (within the temples). The cortex is the major information storage and processing region of the brain.
Behind and below the cortex is the cerebellum (little brain), known to participate in movement and motor coordination. The cerebellum attaches to the top of the brainstem, a region that controls automatic functions including respiration and heartrate.