Perception of Vocal Tremor After Deep Brain Stimulation in Varying Speech Contexts

Vocal tremor (VT) is a difficult to treat voice problem characterized by periodic modulations of fundamental frequency and vocal intensity. VT is easier to perceive during sustained phonation as compared to connected speech. Previous studies have demonstrated improvements in perception of VT during sustained phonation after undergoing deep brain stimulation (DBS) for treatment of essential tremor. However, few studies have investigated perception of VT in connected speech contexts. The purpose of this preliminary study was to examine differences in perception of VT severity before and after thalamic DBS across sustained phonation and connected speech contexts.

Single arm, pre-post design.

Nine adult participants diagnosed with VT undergoing thalamic DBS for treatment of essential tremor participated in this investigation. Perceptual voice evaluation of sustained vowel phonation and two connected speech samples, one loaded with primarily voiceless and the other with voiced speech sounds, were conducted preDBS and postDBS treatment by four expert listeners. Overall severity of the dysphonia and the "unsteadiness" of the voice were evaluated using visual analog scales. Paired t tests were employed for statistical comparisons.

There was good to excellent intra- and inter-rater reliability between expert listeners. We observed a significant interaction for speech context (sustained, voiced, voiceless) and time (preDBS, postDBS) for perceptual ratings of overall severity and unsteadiness. Tests revealed significant reductions in overall severity and unsteadiness postDBS treatment in the sustained vowel and voiced sentence contexts.

Reductions in VT severity after DBS are most evident in sustained vowel analysis but also can be detected in connected speech. Future research on VT and its treatments, including DBS, should carefully consider the choice of speech contexts, as these can influence the perceived effectiveness of therapy. Overall, our findings also add to the growing evidence that DBS may be a valuable treatment for VT.