No prepulse inhibition deficits in patients with unipolar depression

Prepulse inhibition (PPI) has been widely used as a neurophysiological measure of the early preattentive stages of information processing and is used as an operational measure of sensorimotor gating [Braff and Geyer, 1990]. PPI is the normal unlearned suppression of the startle reflex when the intense startling stimulus is preceded by a weak acoustic prepulse. PPI of the startle reflex represents a general ability to inhibit responses to external (auditory, visual, and tactile) and internal (thoughts and impulses) stimuli. Several studies showed that PPI is reduced in a variety of neuropsychiatric disorders, such as schizophrenia, obsessive-compulsive disorder, acute psychotic mania, and panic disorder. It has been suggested that the disorders in which PPI is deficient are characterized by ‘‘a loss of the normal ability to suppress or gate irrelevant sensory, motor or cognitive information. This loss of ‘gating’ may be experienced as intrusive thoughts, sensory information, or adventitious movements or behaviors’’ [Swerdlow et al., 1992, p 177]. Here, acoustic startle reactivity, PPI (30, 60, 120, 240, and 2000 ms interstimulus intervals), and habituation were assessed in 19 non-psychotic patients with unipolar depression and 19 ageand gender-matched healthy controls. Five patients were unmedicated; patients received an antidepressant therapy with serotonin-reuptake-inhibitors, serotonin-noradrenalin-reuptake-inhibitors, or tricyclic antidepressants. One patient was medicated with Hypericum extract. All patients were recruited at the Psychiatric Services of Aargau Canton. The diagnosis was based on an individual semi-structured psychiatric interview using the German version of the International Diagnostic Checklists [Hiller et al., 1996]. The study protocol and consent forms were reviewed and approved by the Ethics Committee of the Psychiatric Services of Aargau Canton. Details of the acoustic startle measurement and recruitment of control subjects are described elsewhere [Ludewig et al., 2002; Ludewig et al., in press]. Data were analysed using one-way (percent habitutation) or twoway (percent PPI and startle magnitude) repeated measures analyses of variance (ANOVA). Unipolar depressive patients showed no differences in PPI (Fig. 1), habituation, or startle magnitude compared to the control group. There was also no dif ference in these startle measures when unmedicated vs. medicated depressive patients were compared. The habituation results are in accordance with Taiminen et al. [2000] who found normal habituation in non-psychotic depression but reduced habituation in psychotic depression. Further investigations are needed to explain these first PPI results in unipolar depression, especially a study in unmedicated patients or comparison with a similarly medicated clinical control group. Nevertheless, animal studies indicate that antidepressants do not alter PPI [Martinez and Geyer, 1997]. These results suggest that the early preattentive stages of information processing indexed by PPI and habituation of startle are not involved in the pathophysiology of nonpsychotic unipolar depression. In contrast, in the clinical field of this disorder, bipolar patients with acute psychotic mania and patients with panic disorder show deficits in PPI of the acoustic startle reflex [Perry et al., 2002; Ludewig et al., 2002].