Cerebral representation of the anorectum using functional magnetic resonance imaging.
BACKGROUND
Anorectal continence depends not only on the organs of continence but also on cerebral control. There are relatively few data regarding cerebral processing of anorectal continence.


METHODS
Thirteen healthy subjects underwent rectal distension to cause urge increasing to discomfort during functional magnetic resonance imaging (fMRI). In addition, a painful heat stimulus was applied to the skin of the anterior abdominal wall in the dermatome corresponding to the rectum. Voluntary contraction of the anal sphincter was also performed. Subjective rating of stimulus intensity was recorded. Evaluation of the data used a general linear model with Brain Voyager(trade mark).


RESULTS
Subjective sensation of discomfort increased during repeated rectal distension and caused activation in the anterior cingulate gyrus, insula, thalamus and secondary somatosensory cortex seen on fMRI. Perception of rectal urge and discomfort activated the same cerebral regions with differing intensity. Application of a painful thermal stimulus in the corresponding dermatome showed a modification of the response. Voluntary contraction of the anal sphincter led to activation of the motor cortex and increased activity in the supplementary motor cortex and the insula.


CONCLUSIONS
Cerebral representation of the anorectum as mapped by fMRI is intricate and reflects the complexity of the continence mechanism.
Bittorf
B
B
Department of Surgery, University of Erlangen-Nuremberg, Erlangen, Germany. birebi@aol.com
Ringler
R
R
Forster
C
C
Hohenberger
W
W
Matzel
K E
KE
D000328:Adult; D001003:Anal Canal / Q000502:physiology; D000704:Analysis of Variance; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D003672:Defecation / Q000502:physiology*; D005260:Female; D006179:Gyrus Cinguli / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology; D012007:Rectum / Q000502:physiology; D013788:Thalamus / Q000502:physiology