Increased acoustic startle responses in IBS patients during abdominal and nonabdominal threat

Abstract

Background and aims: Visceral hypersensitivity and symptom severity in Irritable Bowel Syndrome (IBS) are both exacerbated by stress. The eye-blink startle response represents a noninvasive measure of central defensive responding. Evidence for central hyperexcitability was studied in IBS patients by examining potentiation of the startle reflex to a nociceptive threat.

Methods: Acoustic startle responses were examined in female IBS patients (n = 42) and healthy controls (n = 22) during cued periods in which an aversive abdominal or biceps stimulation was impossible (safe), possible (imminent threat) or anticipated (period just before the imminent threat), and during a threatening context (muscle stimulation pads attached but no cues for stimulation).

Results: Both groups showed potentiation of startle responses during the imminent threat condition compared with both the anticipation and safe conditions. Compared with controls, IBS subjects showed significantly larger startle responses during anticipation and imminent threat conditions after receiving an initial aversive stimulation. There were no group differences during the context threat manipulation. Moreover, in IBS patients but not controls, higher neuroticism was associated with larger startle responses during safe and anticipation conditions but not imminent threat, whereas anxiety symptoms were negatively associated with startle magnitude during imminent threat.

Conclusions: Female IBS patients show increased startle responses to threat of aversive stimulation at both abdominal and nonabdominal sites compared with controls. The data represent the first demonstration of altered threat potentiated startle in a functional pain condition and provide support for the use of these paradigms in further evaluation of affective mechanisms in these disorders.

Figure 1

Experimental design depicting the first and second baseline periods and the context period, followed by the cued threat procedure. R = rest periods; B = Block; light gray bars = safe periods; dark gray bars = abdominal threat periods; black bars = biceps threat periods; downward arrows = startle stimuli.

Figure 2

Context manipulation results. ASR magnitude during the first and second set of six baseline startle trials and the six context threat trials. Values are estimated means (with standard error bars) for each startle trial. sqrt µV = square root transformed microvolts.

Figure 3

ASRs for the cued threat procedure averaged over Blocks. Values are estimated means (with standard error bars) for each condition, Anticipation and threat conditions are averaged over threat type (abdominal and arm). Safe includes both the early and late trials of the safe period. Significance is indicated for group differences in magnitude of ASRs between safe and anticipation and safe and imminent threat conditions. sqrt µV = square root transformed microvolts.

Figure 4

ASRs for the cued threat procedure including Block. Values are estimated means (with standard error bars) for each condition over the three blocks. Anticipation and threat conditions are averaged over threat type (abdominal and arm). Safe includes both the early and late trials of the safe period. Significance is indicated for group differences in magnitude of ASRs between safe and anticipation and safe and imminent threat conditions. sqrt µV = square root transformed microvolts.

Figure 5

Estimated mean ASRs (and standard errors) for IBS patients within 1 SD of the mean and those >1 SD above and below the mean on neuroticism (EPQ-R) for the three cued threat conditions. sqrt µV = square root transformed microvolts.

Figure 6

Estimated mean ASRs (and standard errors) for IBS patients within 1 SD of the mean and those >1 SD above and below the mean on anxiety symptoms HAD-A) for the three cued threat conditions. sqrt µV = square root transformed microvolts.