Defecatory urge increases cognitive control and intertemporal patience in healthy volunteers

Past research has demonstrated that moderate urge to urinate improves inhibitory control, specifically among participants with higher behavioral inhibition sensitivity (BIS). The effect was absent when the urge exceeded intolerable level. The present research examines whether rectal distension-induced urge to defecate has similar effects.

The moderate and high defecatory urge were induced by rectal distension in healthy volunteers (n = 35), while they completed Stroop task and monetary delay discounting task. The difference of average reaction time between incongruent and congruent trials in the Stroop task (Stroop interference) and the preference for larger-later rewards in the delay discounting task were the primary outcomes.

Participants with high BIS (n = 17) showed greater ability to inhibit their automatic response tendencies, as indexed by their Stroop interference, under moderate urge relative to no urge (128 ± 41 ms vs 202 ± 37 ms, t₆₄  = 2.07; P = 0.021, Cohen's d: 0.44), but not relative to high urge (154 ± 45 ms, t₆₄  = 1.20; P = 0.12, Cohen's d: 0.30). High BIS participants also showed a higher preference for larger-later reward in the delay discounting task under high (odds ratio = 1.51 [1.02-2.25], P = 0.039) relative to no urge, but not relative to moderate urge (odds ratio = 1.02 [0.73-1.42], P = 0.91). In contrast, rectal distension did not influence performance on either of the tasks in participants with low BIS (n = 18).

These findings may be interpreted as a "spill-over" effect of inhibition of the urge to defecate to volitional cognitive control among healthy participants with high BIS.