despite the fact that they would prefer not to do so when it is socially inappropriate. Tics are described as semi-voluntary or unvoluntary, because they are not strictly involuntary: they may be experienced as a voluntary response to an unwanted, premonitory urge. Tics are experienced as irresistible and must eventually be expressed. People with Tourette syndrome are sometimes able to suppress their tics for limited periods, but doing so often results in an explosion of tics afterward. The control exerted (from seconds to hours at a time) may merely postpone and exacerbate the ultimate expression of the tic. In alien hand syndrome, the affected individual's limb will produce unintentional movements without the will of the person. The affected limb effectively demonstrates 'a will of its own.' The sense of agency does not emerge in conjunction with the overt appearance of the purposeful act even though the sense of ownership in relationship to the body part is maintained. This phenomenon corresponds with an impairment in the premotor mechanism manifested temporally by the appearance of the readiness potential recordable on the scalp several hundred milliseconds before the overt appearance of a spontaneous willed movement. Using functional magnetic resonance imaging with specialized multivariate analyses to study the temporal dimension in the activation of the cortical network associated with voluntary movement in human subjects, an anterior-to-posterior sequential activation process beginning in the supplementary motor area on the medial surface of the frontal lobe and progressing to the primary motor cortex and then to parietal cortex has been observed. The sense of agency thus appears to normally emerge in conjunction with this orderly sequential network activation incorporating premotor association cortices together with primary motor cortex. In particular, the supplementary motor complex on the medial surface of the frontal lobe appears to activate prior to primary motor cortex presumably in associated with a preparatory pre-movement process. In a recent study using functional magnetic resonance imaging, alien movements were characterized by a relatively isolated activation of the primary motor cortex contralateral to the alien hand, while voluntary movements of the same body part included the natural activation of motor association cortex associated with the premotor process. The clinical definition requires "feeling that one limb is foreign or has a will of its own, together with observable involuntary motor activity" (emphasis in original). This syndrome is often a result of damage to the corpus callosum, either when it