Regional brain activation due to pharmacologically induced adrenergic interoceptive stimulation in humans

Objective: Identifying the brain regions associated with visceral sensory activation and awareness (interoception) was a neglected area of neural science until quite recently despite being essential to a comprehensive understanding of psychosomatic processes, baroreception, and higher brain functions such as fear and anxiety, other emotions, and pain. Methods: In this study regional changes in the cerebral metabolic rate for glucose were determined with positron emission tomography in response to cardiovascular-respiratory activation induced in healthy humans by beta-adrenergic stimulation produced with intravenous isoproterenol, which acts predominantly in the periphery because of minimal transport across the blood-brain barrier. Results: Interoceptive activation raised heart rate to approximately 120 beats per minute, produced somatic and to a lesser extent psychological symptoms, and significantly increased cerebral glucose metabolism in the left primary somatosensory cortex and medial portion of the cingulate gyrus; right insular cortex showed a trend toward an increase that was significant in homogeneous subgroups of right-handed or female subjects. Conclusions: These results demonstrate the involvement of specific brain regions as well as hemispheric laterality of function in visceral perception, and they suggest that during emotional reactions involving changes in visceral organ function, activation of some of the brain regions observed could be due specifically to interoceptive processes.