P131. Vibrotactile stimulation as a novel method to detect malingered attention or sensory deficits

Introduction To our knowledge there exist no objective methods for the clinical validation of reactions after tactile stimulation although the prevalence of symptom aggravation is high in compensation seeking context (18–40%, Axelrod et al., 2000; Binder, 1993; Mittenberg et al., 2002). In order to develop an electrophysiological method for symptom validation after vibrotactile stimulation we investigated the tactile stimulation of mechanical receptors of single sensory qualities with varied stimulation principles (mechanical pulse, vibration, coating, indentation, passive movement) and established a clinical routine. Methods In the present work LRP (lateralized readiness potentials) and NIRS (near-infrared spectroscopy) were recorded after vibrotactile stimulation of the thumb (60 Hz) in 40 healthy controls and 40 subjects with an episode of depression. Tactile SEP (somatosensory evoked potentials) were conducted to make sure that the stimuli were perceived by the subjects. In condition I the subjects were instructed to react to a vibrational stimulus with least possible delay by pushing a button, in condition II an additional time delay or a lack of reaction was asked to be executed. Stimulus- and response-locked LRP and activation patterns of the NIRS signal (Oxy-Hb and Deoxy-Hb) were compared statistically between both the conditions and the subject groups. Results In condition II the reaction-time was significantly longer and its dispersion was greater ( p p p p Conclusion If our results can be replicated in subjects with substantial brain lesions, a novel objective validation method for both sensory deficits and malingered attention deficits might result. As vibrotactile stimulators have only limited availability yet, EEG and surface myography are used as common techniques. If available, this novel method can be easily implemented to routine procedures.