Human forebrain activation by visceral stimuli

Visceral function is essential for survival. Discreet regions of the human brain controlling visceral function have been postulated from animal studies (Cechetto and Saper 1987 J. Comp. Neurol. 262:27-45) and suspected from lethal cardiac arrythmias (Cechetto 1994 Integr. Physiol. Behv. Sci. 29:362-373). However, these visceral sites remain uncharted in the normal human brain. We used 4-Tesla functional magnetic resonance imaging (fMRI) to identify changes in activity in discrete regions of the human brain previously identified in animal studies to be involved in visceral control. Five male subjects underwent heart rate (HR) and/or blood pressure (BP) altering tests: maximal inspiration (MX), Valsalva's maneuver (VM), and isometric handgrip (HG). Increased neuronal activity was observed during MX, VM, and HG, localized in the insular cortex, in the posterior regions of the thalamus, and in the medial prefrontal cortex. To differentiate special visceral (taste) regions from general visceral (HR, BP) regions in these areas, response to gustatory stimulation was also examined; subjects were administered saline (SAL) and sucrose (SUC) solutions as gustatory stimuli. Gustatory stimulation increased activity in the ventral insular cortex at a more inferior level than the cardiopulmonary stimuli. The observed neural activation is the first demonstration of human brain activity in response to visceral stimulation as measured by fMRI.