The enlarged caudate nucleus detected in the brain of the 7-year-old autistic subject is consistent with MRI reports documenting an increased volume of basal ganglia, including the caudate, in autism [54, 55, 66, 99]. A disproportionate increase of the caudate nucleus volume [66] suggests that in brains of some autistic individuals, extended neurogenesis within the subependymal cell layer may contribute to abnormal growth of the caudate nucleus. A similar process has been observed in the brains of people with Huntington disease, showing enhanced neurogenesis in the subependymal layer and suggesting renewal of the neuronal population in a degenerating caudate nucleus [26]. The caudate nucleus is a part of the fronto-striatal network involved in several functional domains that are impaired in autism, including lower order repetitive motor behavior; intense circumscribed patterns of interests and higher order rituals and compulsions [41], and defects in cognitive functions [19, 109], planning and problem-solving skills [78, 98], short- and long-term memory [40] and learning [88].
