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Abstract
Previous studies in animals and humans suggest the periaqueductal grey region (PAG)
is a final integration station between the brain and laryngeal musculature during
phonation. To date, a limited number of functional magnetic neuroimaging (fMRI) studies
have examined the functional connectivity of the PAG during volitional human phonation.
An event-related, stimulus-induced, volitional movement paradigm was used to examine
neural activity during sustained vocalization in neurologically healthy adults and
was compared to controlled exhalation through the nose. The contrast of vocalization
greater than controlled expiration revealed activation of bilateral auditory cortex,
dorsal and ventral laryngeal motor areas (dLMA and vLMA) (p<0.05, corrected), and
suggested activation of the cerbellum, insula, dorsomedial prefrontal cortex (dmPFC),
amygdala, and PAG. The functionally defined PAG cluster was used as a seed region
for psychophysiological interaction analysis (PPI) to identify regions with greater
functional connectivity with PAG during volitional vocalization, while the above functionally
defined amygdala cluster was used in an ROI PPI analysis. Whole-brain results revealed
increased functional connectivity of the PAG with left vLMA during voicing, relative
to controlled expiration, while trend-level evidence was observed for increased PAG/amygdala
coupling during voicing (p=0.07, uncorrected). Diffusion tensor imaging (DTI) analysis
confirmed structural connectivity between PAG and vLMA. The present study sheds further
light on neural mechanisms of volitional vocalization that include multiple inputs
from both limbic and motor structures to PAG. Future studies should include investigation
of how these neural mechanisms are affected in individuals with voice disorders during
volitional vocalization.