Ventral medial prefrontal cortex and cardiovagal control in conscious humans.
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The autonomic nervous system plays a critical role in regulating the cardiovascular responses to mental and physical stress. Recent neuroimaging studies have demonstrated that sympathetic outflow to the heart is modulated by the activity of the anterior cingulate cortex (ACC). However, the cortical modulation of cardiovagal activity is still unclear in humans. The present study used functional MRI to investigate the cortical network involved in cardiovagal control. Seventeen healthy individuals performed graded handgrip exercise while heart rate (HR) and cortical activity were recorded. Muscle sympathetic nerve activity (MSNA), mean arterial pressure (MAP) and HR were measured while participants repeated the same protocol in a parallel experiment session. The handgrip exercise elevated HR and MAP without concurrent elevations in MSNA supporting earlier conclusions that the cardiovascular responses are mainly modulated by vagal withdrawal. The imaging data showed activation in the insular cortex, thalamus, parietal cortices and cerebellum during the exercise period. Consistently across all the participants, the HR response correlated with the deactivation in the ventral medial prefrontal cortex (vMPFC), which has substantial anatomical connection with the subcortical autonomic structures. The deactivation of the vMPFC was independent of the motor control and was observed commonly in both left and right hand exercise. Stronger vMPFC deactivation was observed when participants completed a higher intensity exercise that elicited a larger HR response. Our findings support the hypothesis that the vMPFC is involved in modulating the vagal efferent outflow to the heart and the suppression of its activity elevates cardiovascular arousal in conscious humans.