[Basal ganglia and psychiatric disorders: an experimental validation]

Abnormal movements and behavioral disorders are characteristic manifestations observed in certain neuropsychiatric diseases such as Tourette's syndrome or Huntington Disease. Together with brain imaging findings, the clinical data could suggest a relationship with basal ganglia dysfunction. In the first part of this review, we recall the anatomic relationships existing, via segregated cortico-cortical circuits, between these structures and the cortical areas having motor and cognitive or motivational-emotional attributes. This structure suggests that in pathologies like Parkinson's or Huntington disease cognitive and motivational-emotional disorders as well motor disturbances could be related to lesions or dysfunctions involving individual or combined zones of the basal ganglia. The second part of the paper focuses on a description of the various methodologies used to explore these relationships: behavioral, anatomic and brain imaging methods are used in non-human primate models in order to reproduce motor and behavioral disturbances and to determine the neuronal circuits involved. Microinjection of bicucullin into the external globus pallidus has been found to induce localized and reversible neuronal activation. Abnormal movements can be obtained from the motor territory of the external globus pallidus whereas hyperactivity with attentional deficit or stereotypies have been obtained from the associative or limbic territory of the same structure. In the striatum, the same pharmacological activation can induce either abnormal movements from motor and associative functional territories or behavioural changes with hyperactivity or, on the contrary, hypoactivity from associative functional territory with stereotyped behavior and sexual manifestations when the microinjections were done in the limbic striatum. Anatomic studies as well as brain imaging using PET confirm the involvement of segregated anatomic pathways through the basal ganglia in behavioral as well as motor disorders.