Use of positron emission tomography and cortical evoked potentials in the evaluation of visceral sensation from the gastrointestinal tract

Abstract

USE OF POSITRON EMISSION TOMOGRAPHY AND CORTICAL EVOKED POTENTIALS IN THE EVALUATION OF VISCERAL SENSATION FROM THE GASTROINTESTINAL TRACT. RD Rotbstein, M Stecker, A Ouyang. Departments of Medicine, University of Pennsylvania, Philadelphia, PA and The Milton S. Hershey Medical Center, Pennsylvania State University, Hershey, PA. The central representation of visceral sensations have not been well defined in humans. ‘l’he use of positron emission tomography (PET) and cortical evoked potentials (EP) allows for anatomical localization of perceived sensation from the gastrointestinal tract. Aim: To determine the regions of the brain involved in sensing rectal sensation by measurement of cerebral blood flow (CBF) by PET and localization by EP. Methods: Standard lo-20 electrodes were placed in 5 normal subjects. A balloon catheter was inserted 15 cm into the rectum and connected to a rapid balloon inflation device which was triggered by a Viking 11 EP machine. Balloon volumes of 0.5, 10, and 20 cc were used and subject sensation was graded 0 to 10. PET scans were performed with 1 5 O-H20 using the equilibrium method during rectal balloon distension and were compared to the subject’s MRI image. Changes in cerebral blood flow (CBF) and amplitude of the waveforms by EPs were measured. Results: No subjective sensation, EPs or change in CBF was seen at 0 cc. A significant change in CBF occurred at a balloon volume of 10 cc in the orbital gyrus (p=O.O24), thalamus (p=O.O49), and pre-and post central gyrus (p=O.OSO). Trends toward significant increases in CBF were noted in the insula, putamen, cerebellem, medial frontal gyrus and cuneus. For EP, two peaks were noted (Nl, N2). There was a linear relationship between the amplitude of Nl and balloon volume (p=.O4) and between the amplitude of N2 and balloon volume (p= 0.001). There was no further increase in CBF and the amplitude of Nl and N2 at 20 cc. The subjective score was highly variable between subjects and there was not a linear relationship between sensation and balloon volume. EP or CBF. Conclusion: There is a plateau in CBF and EP, but not subjective sensation, to balloon distension over 10 cc. These findings suggest the probability of more than one pathway involved in the perception of visceral sensation. PET and EP are useful tools in mapping the cerebral representation for visceral sensation.