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Increased Acoustic Startle Responses in IBS Patients During Abdominal and Nonabdominal Threat

From the Center for Neurobiology of Stress (B.D.N., J.S.L., L.K., L.C., E.A.M., E.O.); Departments of Medicine (L.C., E.A.M.); Physiology (E.A.M.); Psychiatry and Biobehavioral Sciences (B.D.N., J.S.L., L.K., M.G.C., E.A.M., E.O.), David Geffen School of Medicine, UCLA, Los Angeles, California; Research Service, VA Greater Los Angeles Healthcare System (B.D.N., H.I.), Los Angeles, California; School of Psychology (A.M.W.), Griffith University, Australia; Department of Psychiatry (H.N.), Nara Medical University, Nara, Japan; and Brain Research Institute (E.A.M., E.O.), UCLA, Los Angeles, California.

Address correspondence and reprint requests to Bruce D. Naliboff, PhD, Center for Neurobiology of Stress; CURE, Building115, Room 223, 11301 Wilshire Boulevard, Los Angeles, CA 90073. E-mail: naliboff{at}ucla.edu

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.

Key Words: irritable bowel syndrome • functional bowel disorders • acoustic startle response • fear-potentiated startle

Abbreviations: ASR = acoustic startle response; IBS = irritable bowel syndrome; GI = gastrointestinal; HADS = Hospital Anxiety and Depression Scales; EPQ-N = Neuroticism scale from the Eysenck Personality Questionnaire; EMG = electromyogram; EOG = electrooculogram; SS = startle stimulus; IGCM = individual growth curve modeling; ANOVA = analysis of variance; ANCOVA = analysis of covariance.

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