The neurodevelopmental frontostriatal disorders: evolutionary adaptiveness and anomalous lateralization

The frontostriatal system (dorsolateral prefrontal cortex, lateral orbitofrontal cortex, anterior cingulate, supplementary motor area, and associated basal-ganglia structures) is subject to a range of neurodevelopmental disorders: Tourette's syndrome (TS), obsessive compulsive disorder (OCD), attention deficit hyperactivity disorder (ADHD), schizophrenia (SCZ), autism, and probably depression. The system is responsible for our adaptive responses (initiation, execution, or withholding) to environmental situations, and the above disorders, involving effectively excessive release or withholding of various types of response, are all a consequence of changes in specific frontostriatal regions. The disorders all have a genetic component, and their persistence in the genome indicates that their clinical manifestations may also be associated, perhaps in low levels in close relatives, with certain adaptive advantages in given situations. Thus autism is associated with computational careers, depression with literary creativity, SCZ with lateral thinking and the Odyssean personality, ADHD with an Ice-Age readiness to respond, OCD with a focused range of interests, and TS with competitive sports and jazz improvisation. The disorders are all highly comorbid, and which one predominantly manifests may depend on how the frontostriatal system happens to be compromised as a result of inherited genetic predispositions and environmental contingency. We review the adaptive nature of the various subclinical manifestations and the evidence for concomitant phenomena (possibly epiphenomena): alterations in structural, functional, and behavioral lateralization in each syndrome. Indeed it is not clear that altered lateralization in frontostriatal disorders of a neurodevelopmental origin generally has any adaptive significance; it may often simply serve as a marker for altered regulatory function of the frontostriatal system, alterations which in low genetic dosage or penetrance continue to play an adaptive role in clinically unaffected close relatives of probands, but which, in high dosage or penetrance in the probands themselves, are generally deleterious.