Network Imaging in Parkinsonian and Other Movement Disorders: Network Dysfunction and Clinical Correlates.

Parkinson's disease (PD) is classically defined as a disease of progressive dopaminergic dysfunction, thus explaining many of the levodopa-responsive motor features. However, even early in the disease, non-motor symptoms can appear, affecting sleep, cognition, and behavior. This implies the involvement of more widespread circuitry beyond the basal ganglia. In addition, the varied clinical presentation and the clinical overlap between PD and other diseases of dopamine degeneration (referred to as atypical parkinsonian syndromes), particularly early in the disease, have complicated diagnosis, treatment, and clinical trials. The increased use of functional imaging techniques, which can identify and quantify widespread functional networks, has provided insights into understanding these disorders beyond dopaminergic degeneration. In this chapter, we summarize such work as it relates to pathophysiology, diagnosis, progression, and treatment of parkinsonian disorders. We also briefly highlight findings in another neurodegenerative disorder, Huntington's disease.