ABSTRACT
An important feature for understanding the role of the basal ganglia in movement is the presence of two routes through the basal ganglia circuitry with opposite effects on firing of thalamic, and hence cortical neurons. The direct pathway uses the γ-aminobutyrate (GABA)/substance P/dynorphin medium spiny striatal neurons which inhibits GABAergic outflow of the globus pallidus pars interna and SNpr to the thalamus. Motor disorders arising from dysfunction of the basal ganglia, whether caused by disease, or by lesions in animal studies, fall into two distinct categories, hyperkinesias and hypokinesias. The prototypical hypokinetic disorder is Parkinson's disease, characterized by rigidity, bradykinesia and tremor. Huntington's disease is a progressive neurodegenerative disorder in which symptoms begin between 40 and 50 years of age. Obsessive–compulsive disorder is a chronic psychiatric disorder in which a person is unable to prevent themselves endlessly repeating the same actions or thoughts.
