P 22 Effects of multisensory feedback on tremor severity in essential tremor

Abstract

Introduction : Essential tremor (ET) amplitude is modulated by visual feedback during target-driven movements: In a grip force task, tremor amplitude increases during large-scale visual feedback compared to low-scale visual feedback. It has not been examined whether visual feedback exclusively modulates action tremor severity or if an increase of other afferent input like auditory information has a modulatory effect on tremor amplitude as well. Also, it is unknown whether the sensory signal itself directly affects the tremor generating network or if the effect is rather indirect: enhanced sensory feedback during targeted driven movements might cause arousal/psychological stress. We hypothesized that (1) amplitude of ET is modulated by variation of auditory feedback in the absence of visual feedback in a force tremor paradigm; (2) increase of tremor amplitude coincides with pupillary dilation as a measure of arousal / psychological stress, independently of the quality of sensory feedback Patients & Methods : 14 ET patients conducted a computer-based experiment in which they were asked to match a target force in a force sensor using their thumb and index finger. The quality of them matching the target force was fed back to the participant visually, auditory or a combination of both. For the visual feedback, 2 bars were displayed on a screen, with the distance between these bars decreasing with approximation of the target force. In auditory feedback, a target tone of 440Hz was asked to match by a second tone which changed pitch when approximating the target force. The amplitude of feedback was manipulated via a scaling factor resulting in a large scale and a small scale feedback condition. To characterize the performance (RMSE to target force) and the tremor severity (Power 4-12 Hz) a 3x2 ANOVA was conducted. To control for arousal / psychological stress-induced via the task, pupillometry was recorded. Results : First results showed a comparable deviation from the target force (RMSE) during the experiment in all three sensory feedback modalities. Additionally, tremor severity did not differ between sensory feedback modalities. The ANOVA revealed an effect of the scaling factor on the tremor severity (Power 4-12Hz) for the visual and also for the auditory feedback condition. Pupillometry consistently showed a significantly increased pupil diameter during the large-scale visual- and auditory feedback conditions compared to the small-scale feedback conditions. Conclusion : Our preliminary findings suggest that action tremor in ET is firstly modulated not only by visual but also auditory feedback in a comparable manner and seems to be modality independent. Secondly, arousal / cognitive stress, as measured here by the pupil size, could mediate the increase of tremor amplitude. Further work is required better understand the role of these two possible mechanisms underlying target-related tremor.