1. The cortical topography of human anorectal musculature
Geoffrey K. Turnbull*, Shaheen Hamdy‡, Qasim Aziz‡, Krishna D. Singh§, David G. Thompson‡ 
Gastroenterology 
Volume 117, Issue 1, Pages (July 1999)
DOI: /S (99)
Copyright © 1999 American Gastroenterological Association Terms and Conditions

2. Fig. 1
Individual examples of the averaged EMG responses recorded from the anal sphincter, rectum, right tibialis, and left tibialis muscles after cortical stimulation. (A) EMG responses in all four muscle groups after stimulation of a site close to the vertex of the scalp. The morphology of each response is different, suggesting that each was generated from an independent source and that the latency of the anal sphincter response is longer than that of the rectal response, both being shorter than the tibial responses. Arrows indicate the onset of anal and rectal responses. (B) EMG responses after stimulation of a site over the right hemisphere. Both anal and rectal responses have been evoked, whereas, as expected, only the contralateral left tibial response is evoked. (C) EMG responses after stimulation of a site over the left hemisphere. Again, both anal and rectal responses are evoked, whereas only the contralateral right tibial response is evoked. (D) Responses to stimulation of a second midline scalp site. In contrast to the responses shown in A, the rectal response has been evoked in the absence of an anal response, indicating that the rectal response was unlikely to have been induced by contraction of the anal sphincter.
Gastroenterology  , 32-39DOI: ( /S (99) )
Copyright © 1999 American Gastroenterological Association Terms and Conditions

3. Fig. 2
(A–C) Topographic scalp maps of the cortical representation of the anal and rectal responses for 3 subjects. All plots are oriented as viewed from above, with the vertex of each plot marked with an X. Scale indicates the percentage of the amplitude of the maximum response evoked from either hemisphere for each muscle group in each subject. Subject in A has bilateral anal and rectal representation, whereas subjects in B and C show clear lateralization of both the anal and rectal responses to the left and right hemispheres, respectively.
Gastroenterology  , 32-39DOI: ( /S (99) )
Copyright © 1999 American Gastroenterological Association Terms and Conditions

4. Fig. 3
Individual data from 1 subject shown as a series of right lateral oblique surface-rendered brain MRI images onto which scalp map data have been colocalized. Arrow indicates central sulcus. The areas of cortex under the colocalized representation of the anal, rectal, right leg, and left leg responses are shown. The responses from all four muscle groups localize to the superomedial motor cortex (Brodmann area 4), but they have different morphologies and extents of representation. In particular, in this individual, the anal and rectal responses have bilateral representation, whereas the leg responses show clear lateralization to the contralateral hemisphere.
Gastroenterology  , 32-39DOI: ( /S (99) )
Copyright © 1999 American Gastroenterological Association Terms and Conditions