In an attempt to integrate the clinical and experimental evidence for both cortical and subcortical neurophysiological dysfunction, it has been proposed that the disturbances of sensory modulation and motility reflect the pathophysiological mechanism and that the other abnormal behaviors can be understood as consequences of distorted sensory input. This suggests a neurophysiological dysfunction involving a cascading series of interacting neuronal loops in the brain stem and diencephalon which subserve modulation of sensory input. Some of the same systems modulate motor output in response to sensory input. The rostral projections from these structures include those to the hippocampus, limbic cortex, neostriatum, and parietal cortex. Parietal structures influence the direction of attention to stimuli of emotional significance, integrating sensory input from association cortex and thalamic centers with limbic and reticular input.
Output is to regions involved with motor responses to emotionally significant stimuli.
Autistic children suffer from distortions of directed attention and fail to sustain motor responses such as eye contact to socially relevant stimuli. Their emotional, cognitive, and language deficits suggest failure of emotional surveillance, a function attributed to dorsal parietofrontal structures. Brain stem and diencephalic centers project rostrally to telencephalic structures and these, in turn, modify brain stem and diencephalic function. In this model, hypotheses of rostrally and caudally directed sequences of pathoneurophysiological dysfunction in autism merge, so that autism can be explained in terms of a system dysfunction involving brain stem and related diencephalic behavioral systems and the impact of such dysfunction on selected higher neural structures that elaborate and modulate the activities of the lower centers. The model implies that autism is a neurophysiological disease, in which the hypothesized mechanism is at the interface between sensory and information processing and involves a dysfunction of directed attention, and anatomical studies suggest that limbic system pathology could be a central component of the proposed system dysfunction underlying the deviant attentional and emotional behavior.