Hypophonia in Parkinson's disease: Neural correlates of voice treatment revealed by PET

Objective: To investigate the neural correlates of hypophonia in individuals with idiopathic PD (IPD) before and after voice treatment with the Lee Silverman Voice Treatment method (VT) using ¹⁵O-H₂O PET. Methods: Regional cerebral blood flow (rCBF) changes associated with overt speech-motor tasks relative to the resting state were measured in the IPD subjects before and after VT, and in a group of healthy control volunteers. Results: Behavioral measures of voice loudness significantly improved following treatment. Before VT, patients had strong speech-related activations in motor and premotor cortex (M1-mouth, supplementary motor cortex [SMA], and inferior lateral premotor cortex [ILPm]), which were significantly reduced post-VT. Similar to the post-treatment session, premotor activations were absent (SMA) or below statistical threshold (M1-mouth) in the healthy control group. In addition, following VT treatment, significant right-sided activations were present in anterior insular cortex, caudate head, putamen, and dorsolateral prefrontal cortex (DLPFC). Finally, the VT-induced neural changes were not present with transient experimenter-cued increases of loudness in VT-untreated patients. Conclusions: Effective improvement of IPD hypophonia following voice treatment with VT was accompanied by a reduction of cortical motor-premotor activations, resembling the functional pattern observed in healthy volunteers and suggesting normalization, and additional recruitment of right anterior insula, caudate head, putamen, and DLPFC. This treatment-dependent functional reorganization suggests a shift from an abnormally effortful (premotor cortex) to a more automatic (basal ganglia, anterior insula) implementation of speech-motor actions.