P41. New electrophysiological findings in the detection of malingering attention deficits in subjects with an episode of depression compared to healthy subjects

Abstract

Introduction The history of research in the detection of deception goes back to the 1880’s. A first overview about different electrophysiological methods was given by Scott (1948). Over the time various methodologies were established, notably applying neuropsychological test procedures. As until now there is no possibility of validating reaction-times objectively, the first aim of the present studies was to identify activation patterns of the NIRS (near-infrared spectroscopy) and specific parameters of LRP (lateralized readiness potentials) indicating a delay of motor response in terms of malingering attention deficits. Secondly we investigated whether there are differences in the named parameters between healthy and depressive subjects. Methods Using a repeated measures design, EEG, NIRS, the electromyogram of thumb muscles and the reaction-time of 46 healthy and 41 depressive subjects were recorded. Thereby an already established test for symptom validation, the Structured Interview of Malingered Symptomatology (SIMS), was applied. All subjects were asked to react on a visual stimulus by pushing a button with their thumb: In task I “as fast as they can be”, in task II “with an additional time delay of 0.5 s”. LRP were extracted stimulus- and response-locked and signal analyses were done comprising activation patterns of the NIRS, peak latencies, amplitudes and topographic distribution of the LRP followed by a statistical comparison (ANOVA) between both the conditions and within the subject groups. Results As anticipated, the reaction-time was significantly longer and its dispersion was greater in task II (p 0.001). However, after identification and exclusion of subjects who completed the experiment with poor effort, no differences appeared within the subject groups. For several locations of conduction a significant reduction of amplitudes of stimulus- and response-locked LRP between the conditions occurred: C3, CP1, P3, F3, FC1 (p from 0.05 to 0.001). Again, within the subject groups no major difference was found. Furthermore, in healthy subjects a significant contrast in the NIRS signal derived from the left parietal brain regions was detected (condition II vs. I, p 0.001), whereas in depressive subjects activation patterns in the NIRS in general were weaker. Nevertheless, even in this group differences within the conditions could be shown reproducibly (p 0.01). Conducting the electromyogram of the thumb musculature, a temporal significantly longer pre-innervation before the virtual push of the button was found in condition II. Conclusions Using LRP or NIRS in combination with electromyography of the target musculature allows the assessment of the validity of reaction-times respectively attention deficits. If the results can be replicated in subjects with substantial brain lesions and subjects examined in a compensation seeking context (e.g. medical assessment, in progress), an instrument for the detection of malingered attention deficits might result.