Theta burst stimulation over left cerebellum does not modulate auditory feedback control of vocal production

Abstract

Background: Accumulating evidence has shown significant contributions of the right cerebellum to auditory-motor integration for vocal production. Whether the left cerebellum is likewise involved in vocal motor control, however, remains unclear.

Methods: By applying neuronavigated continuous and intermittent theta burst stimulation (cTBS/iTBS) over the left cerebellar lobule VII (Crus I), the present event-related potential (ERP) study investigated whether the left cerebellum exerts causal effects in modulating auditory feedback control of vocal pitch production. After receiving cTBS, iTBS, or sham stimulation over the left cerebellum, a group of fifteen young adults produced sustained vowels while hearing their voice unexpectedly shifted in pitch upwards or downwards by 200 cents. The effects of cerebellar stimulation were assessed by measuring the vocal and ERP (N1/P2) responses to pitch perturbations across the conditions.

Results: When compared to sham stimulation, cTBS or iTBS over the left cerebellar lobule VII (Crus I) led to no systematic changes in vocal compensations for pitch perturbations in auditory feedback. Also, the cortical N1/P2 responses did not vary significantly across the three stimulation sessions.

Conclusion: These findings present the first neurobehavioral evidence suggesting that the left cerebellum is not causally associated with auditory feedback control of vocal production. Together with previously reported causal effects of the right cerebellum in modulating vocal pitch regulation, the present study lends support to the hypothesis that there is a functional lateralization of the cerebellum in vocal motor control though auditory feedback.

Keywords: auditory feedback; event-related potential; left cerebellum; speech motor control; theta burst stimulation.

FIGURE 1

The site of theta burst stimulation (TBS) stimulation located in the left cerebellar lobule VII (Crus I), which was identified on individual MRIs in coronal, axial, and sagittal views of the brain with the help of a neuronavigation system.

FIGURE 2

Overview of the frequency-altered feedback (FAF) paradigm. From top to bottom: voice f_o contour in cents, auditory feedback containing pitch perturbations in cents, and transistor-transistor logic (TTL) control pulses that signaled the onset of upward and downward pitch perturbations.

FIGURE 3

Grand-averaged voice f_o contours across all participants in responses to pitch perturbations of ±200 cents following continuous theta burst stimulation (cTBS) (blue), intermittent theta burst stimulation (iTBS) (red), and sham (black) stimulation over the left cerebellar lobule VII (Crus I). Time 0 represent the onset of pitch perturbations. CB, cerebellum.

FIGURE 4

Violin plots of the peak magnitudes (A) and times (B) of vocal responses to ±200 cents produced by all participants across the conditions. The shape of the violin shows the kernel density estimate of the data. The white dots and box plots represent the medians and ranges from first to third quartiles of the data sets. The blue, red, and black dots represent the individual vocal responses to pitch perturbations following cTBS, iTBS, and sham stimulation over the left cerebellar lobule VII (Crus I). CB, cerebellum.

FIGURE 5

Grand-averaged event-related potential (ERP) waveforms across all participants in responses to pitch perturbations of ±200 cents in the frontal, fronto-central, and central regions following cTBS, iTBS, and sham stimulation over the left cerebellar lobule VII (Crus I). Time 0 represent the onset of pitch perturbations. CB, cerebellum.

FIGURE 6

Violin plots of the amplitudes and latencies of the N1 (A,B) and P2 (C,D) responses to pitch perturbations of ±200 cents produced by all participants across the conditions. The white dots and box plots represent the medians and ranges from first to third quartiles of the data sets. The blue, red, and black dots represent the individual vocal responses to pitch perturbations following cTBS, iTBS, and sham stimulation over the left cerebellar lobule VII (Crus I). The asterisk indicates a significant difference in the P2 latency between +200 and −200 cents perturbations. CB, cerebellum.