Clinical NeuroscienceShort communicationMechanically evoked cortical potentials: A physiological approach to assessment of anorectal sensory pathways

- Anal and/or rectal hypo- and hypersensitivity are common in many defaecatory disorders.
- Presentation of a novel method to evoke light touch anorectal cortical potentials.
- Selective stimulation of anal canal and rectum, utilizing a 3D printed shield.

BackgroundNormal defaecation involves activation of anorectal mechanoreceptors responsive to pressure and stretch. The aim of this study was to develop selective anal and rectal mucosal light-touch stimulation suitable for measurement of cortical evoked potentials (EPs) in order to explore the sensory arm of these pathways.New methodA novel device was manufactured to deliver selective rectal and/or anal light-touch stimulation using a shielded inter-dental brush mounted on a rotating stepper motor (1 Hz, 1 ms, 15° rotation). Resultant somatosensory EPs recorded with a 32-channel cortical multi-electrode array were compared to those elicited by electrical anorectal stimulation (2 mm anal plug electrode [1 Hz, 1 ms, 10 V]).ResultsEighteen anaesthetized female Wistar rats (body mass 180-250 g) were studied. Electrical and mechanical stimulation provoked similar maximal response amplitudes (electrical anorectal 39.0 μV[SEM 5.5], mechanical anal 42.2 μV[8.1], mechanical rectal 45.8 μV[9.0]). Response latency was longer following mechanical stimulation (electrical anorectal 8.8 ms[0.5], mechanical anal 16.4 ms[1.1], mechanical rectal 18.3 ms[2.5]). The extent of activated sensory cortex was smaller for mechanical stimulation. Sensory inferior rectal nerve activity was greater during anal compared to rectal mechanical in a subgroup of 4 rats. Evoked potentials were reproducible over 40 min in a subgroup of 9 rats.Comparison with existing methodsCortical EPs are typically recorded in response to non-physiological electrical stimuli. The use of a mechanical stimulus may provide a more localized physiological method of assessment.ConclusionsTo the authors' knowledge these are the first selective brush-elicited anal and rectal EPs recorded in animals and provide a physiological approach to testing of anorectal afferent pathways.