Parkinson’s disease (PD) is a progressive neurological disorder characterized by tremor, rigidity, and slowness of movements. PD is associated with progressive neuronal loss of the substantia nigra and other brain structures.¹ It is currently believed that movement symptoms involved in PD caused by interference of motor program execution result form dysfunctional basal ganglia-motor cortex circuits as well as abnormalities in peripheral afferent inputs or central processing.^{2, 3} The successful execution of a voluntary movement critically depends on peripheral sensory feedback. Sensorimotor integration is the process by which sensory input is integrated by the central nervous system and used to assist in motor program execution.³ Patients with PD are more reliant than healthy controls on external sensory information for motor initiation and execution,suggesting that impaired proprioception may play a role in PD symptoms. ⁴

Abbruzzese et al. recently proposed that some types of movement disorder are characterized by a lack of inhibition at multiple levels of the central nervous system and by defective sensorimotor organization.^{5,6 In addition, it has been demonstrated that PD patients, especially in its early stages, exhibits severely depressed frontal responsiveness to sensory stimuli as tested with sensory evoked potentials (SEPs).7,8} Forss and Jousmaki proposed that the secondary somatosensory (SII) cortices also play an important role in sensorimotor integration.⁹ An increasing body of evidence indicates that, in PD patients, the supplementary motor area (SMA) commonly exhibits hypoactivation, while other cortical motor regions, such as the cerebellum, premotor area (PMA), and parietal cortex exhibit hyperactivation while performing motor tasks, compared with normal controls.^10,11

A fundamental question in motor research is how motor planning operations and sensory feedback are implemented in the human brain.¹² Previous studies have indicated that several separate sensory systems are involved in motor planning, including the haptic, visual, and auditory systems. To successfully prepare for and accomplish an action, information from these systems must somehow be integrated. For PD patients, a deficiency may exist in the sensory-motor integration process, and the prefrontal lobe may constitute the neural substrate of this dysfunction.^3,8,13 The lack of a definite correlation with clinical features means that it remains unclear whether abnormalities of sensorimotor integration play a major role in the development of akinesia.

We used multitask functional magnetic resonance imaging (fMRI) to investigate which brain regions are involved in the integration of tactile-motor information, and to determine whether activity in these regions differs when PD patients are compared to normal controls.