RESEARCH ARTICLE S. E. Siegelaar Æ M. Olff Æ L. J. Bour D. Veelo Æ A. H. Zwinderman Æ G. van Bruggen G. J. de Vries Æ S. Raabe Æ C. Cupido J. H. T. M. Koelman Æ M. A. J. Tijssen The auditory startle response in post-traumatic stress disorder Received: 26 May 2005 / Accepted: 24 January 2006 / Published online: 9 March 2006 Ó Springer-Verlag 2006 Abstract Post-traumatic stress disorder (PTSD) patients are considered to have excessive EMG responses in the orbicularis oculi (OO) muscle and excessive autonomic responses to startling stimuli. The aim of the present study was to gain more insight into the pattern of the generalized auditory startle reflex (ASR). Reflex EMG responses to auditory startling stimuli in seven muscles rather than the EMG response of the OO alone as well as the psychogalvanic reflex (PGR) were studied in PTSD patients and healthy controls. Ten subjects with chronic PTSD (>3 months) and a history of excessive startling and 11 healthy controls were included. Latency, amplitude and duration of the EMG responses and the amplitude of the PGR to 10 auditory stimuli of 110 dB SPL were investigated in seven left-sided muscles. The size of the startle reflex, defined by the number of muscles activated by the acoustic stimulus and by the amplitude of the EMG response of the OO muscle as well, did not differ significantly between patients and controls. Median latencies of activity in the sternoclei- domastoid (SC) (patients 80 ms; controls 54 ms) and the deltoid (DE) muscles (patients 113 ms; controls 69 ms) were prolonged significantly in PTSD compared to controls (P<0.05). In the OO muscle, a late response (median latency in patients 308 ms; in controls 522 ms), probably the orienting reflex, was more frequently present in patients (56%) than in controls (12%). In patients, the mean PGR was enlarged compared to controls (P<0.05). The size of the ASR response is not enlarged in PTSD patients. EMG latencies in the PTSD patients are prolonged in SC and DE muscles. The presence of a late response in the OO muscle discrimi- nates between groups of PTSD patients with a history of startling and healthy controls. In addition, the auto- nomic response, i.e. the enlarged amplitude of the PGR can discriminate between these groups. Keywords Post-traumatic stress disorder Æ Startle Æ PGR Introduction Exaggerated motor startle responses are considered to be one of the symptoms in post-traumatic stress disorder (PTSD). Other symptoms include hypervigilance, sleep disturbances, irritability and difficulty to concentrate. The general increase in physiological arousal is hypothesized to be due to an increased noradrenergic function in PTSD (Southwick et al. 1997, 1999; Spivak et al. 1999). Activity of the orbicularis oculi (OO) muscle is used as an indicator for the motor response of the auditory startle reflex (ASR) (Shalev et al. 1997; Orr et al. 1997; Orr and Roth 2000). Enlarged EMG amplitudes in the OO muscle have been described in some groups of PTSD patients, but contradictory results have been published (Metzger et al. 1999; Orr et al. 1997, 2002; Shalev et al. 1992, 2000; Grillon et al. 1996). Increased autonomic responses, such as mean heart rate and psychogalvanic reflex (PGR), due to startling stim- uli have also been reported in PTSD. The effect of an auditory stimulus in PTSD is influenced by the interval between the traumatic experience and the study of the motor startle response. In chronic PTSD patients (interval larger than three months), the physiological response stabilizes (Shalev et al. 2000). The startle reflex consists of a bilateral generalized flexion reflex. Most muscle activity is located in the face S. E. Siegelaar Æ L. J. Bour Æ D. Veelo Æ G. van Bruggen J. H. T. M. Koelman Æ M. A. J. Tijssen (&) Departments of Neurology H2-222 and Clinical Neurophysiology, Academic Medical Centre, P.O. Box 22660, 1100 DD, Amsterdam, The Netherlands E-mail: M.A.Tijssen@amc.uva.nl Tel.: +31-20-5663842 Fax: +31-20-6971438 M. Olff Æ G. J. de Vries Æ S. Raabe Æ C. Cupido Department of Psychiatry, Academic Medical Centre, Amsterdam, The Netherlands A. H. Zwinderman Department of Clinical Epidemiology and Biostatistics, Academic Medical Centre, Amsterdam, The Netherlands Exp Brain Res (2006) 174: 1–6 DOI 10.1007/s00221-006-0413-y