Evidence of the voice-related cortical potential: An electroencephalographic study

The Bereitschaftspotential (BP) is a slow negative-going cortical potential associated with preparation for volitional movement. Studies since the 1960s have provided evidence for a BP preceding speech-related volitional motor acts. However, the BP associated specifically with voice initiation (i.e. a volitional motor act involving bilateral true vocal fold adduction) has not to date been systematically investigated. The current investigation utilizes a novel experimental design to address methodological confounds typically found in studies of movement-related cortical potentials, to demonstrate the existence and localization of generators for the voice-related cortical potential (VRCP). Using high-density EEG, we recorded scalp potentials in preparation for voice onset and for exhalation in a stimulus-induced voluntary movement task. Results showed a slow, increasingly negative cortical potential in the time window of up to 2500 ms prior to the mean onset of phonation. This VRCP peaked at a greater amplitude and shorter latency than the BP associated with exhalation alone. VRCP sources were localized to the anterior rostral regions of the medial frontal gyrus (Supplementary Motor Area (SMA)) and in bilateral laryngeal motor areas before and immediately following the mean initiation of phonation. Additional sources were localized to the bilateral cerebellum and occipital lobe in the time window following the mean onset of phonation. We speculate that these results provide additional support for fine somatotopic organization of the SMA. Further examination of the spatiotemporal change of the VRCP yielded source models which indicated involvement of the laryngeal motor cortices and cerebellum, likely responsible for the initiation and continuation of phonation.