the GPi and GPe via excitatory, glutaminergic pathways. Excitation of the direct pathway leads to disinhibition of the GABAergic neurons of the GPi/SNr, ultimately resulting in activation of thalamic neurons and excitation of cortical neurons. In contrast, activation of the indirect pathway stimulates the inhibitory striatal GABA/enkephalin projection, resulting in suppression of GABAergic neuronal activity. This, in turn, causes disinhibition of the STN excitatory outputs, thus triggering the GPi/SNr inhibitory projections to the thalamus and decreased activation of cortical neurons. While deregulation of either of these pathways can disturb motor output, hyperkinesia is thought to result from overactivity of the direct pathway and decreased activity from the indirect pathway. Hyperkinesia occurs when dopamine receptors, and norepinephrine receptors to a lesser extent, within the cortex and the brainstem are more sensitive to dopamine or when the dopaminergic receptors/neurons are hyperactive. Hyperkinesia can be caused by a large number of different diseases including metabolic disorders, endocrine disorders, heritable disorders, vascular disorders, or traumatic disorders. Other causes include toxins within the brain, autoimmune disease, and infections, which include meningitis. Since the basal ganglia often have many connections with the frontal lobe of the brain, hyperkinesia can be associated with neurobehavioral or neuropsychiatric disorders such as mood changes, psychosis, anxiety, disinhibition, cognitive impairments, and inappropriate behavior. In children, primary dystonia is usually inherited genetically. Secondary dystonia, however, is most commonly caused by dyskinetic cerebral palsy, due to hypoxic or ischemic injury to the basal ganglia, brainstem, cerebellum, and thalamus during the prenatal or infantile stages of development. Chorea and ballism can be caused by damage to the subthalamic nucleus. Chorea can be secondary to hyperthyroidism. Athetosis can be secondary to sensory loss in the distal limbs; this is called pseudoathetosis in adults but is not yet proven in children. Diagnosis Definition There are various terms which refer to specific movement mechanisms that contribute to the differential diagnoses of hyperkinetic disorders. As defined by Hogan and Sternad, "posture" is a nonzero time period during which bodily movement is minimal. When a movement is called "discrete," it means that a new posture is assumed without any other postures interrupting the process. "Rhythmic" movements are those that occur in cycles of similar movements. "Repetitive," "recurrent," and "reciprocal" movements feature a certain bodily or joint position that occur more than once in a period, but not necessarily in a cyclic manner. Overflow refers to unwanted movements that occur