Abnormal cerebral laterality in posttraumatic stress disorder.

Abstract

Different studies’V2 have shown evidence of an augmented startle probe reflex in persons with posttraumatic stress disorder (PTSD). In normal subjects a potentiation of the startle probe reflex amplitude has been observed under conditions of negative emotional or during shock anti~ipation.~ Under conditions without shock anticipation (lack of anticipatory anxiety), the startle response was greater and of shorter latency when the acoustic startle probe stimulus was delivered to the left ear (i.e., right cerebral hemisphere) as opposed to the right ear? whereas under conditions of shock anticipation the right-left difference was in the opposite direction (significant interaction “condition x ear”). These findings suggest that the normally observed right hemispheric dominance of the startle response gets lost under stress; instead, a left hemispheric dominance develops. Other results are in line with this interpretation of a stress-induced abnormal cerebral laterality: under stress the normally observed left hemispheric advantage in processing verbal stimuli gives way to a right hemispheric ad~antage.~.’ Concerning these data it can be hypothesized that subjects with PTSD may show an abnormal cerebral laterality. The hypothesis is supported by data on auditory functions in PTSD subjects8 showing a more pronounced asymmetry in performance scores for right versus left ear stimulation in PTSD subjects than in controls. Data on auditory probe-evoked potential attenuation as an index of hemispheric activity reported by Schiffer et aL9 also hint at an abnormal or altered cerebral laterality in PTSD: subjects with a history of childhood trauma were reported to show a significant left dominant asymmetry during neutral memory, which markedly shifted to the right during unpleasant memory, whereas control subjects without childhood trauma did not display a significant asymmetry during either task or a significant shift between tasks. The present investigation was designed as a pilot study to test the hypothesis of abnormal or altered cerebral laterality in PTSD. Two functions that are dominated