Objective: We aim to further characterise the sensory processing abnormalities previously observed in AOPTD using a novel transcranial Direct Current Stimulation (tDCS) protocol.

Background: AOPTD, the most common form of primary dystonia, is a movement disorder with autosomal dominant inheritance and a reduced penetrance. Abnormal temporal discrimination has been demonstrated in AOPTD patients [1]. It is thought that a prolonged TDT indicates disordered subcortical mechanisms for covert attentional orienting at the level of the superior colliculus. This is supported by evidence of reduced collicular activation on fMRI during an activating task among patients and relatives with an abnormal TDT [2]. tDCS is a non-invasive modality for focally and transiently modulating cortical activity. Previous research has demonstrated that tDCS of the Frontal Eye Field (FEF) can modulate attentional orienting and sensory processing via the superior colliculus [3].

Method: A protocol for tDCS of the left FEF was developed with reference to the existing literature [3]. A current stimulator (Starstim, Neuroelectrics) was used to deliver the tDCS. Anodal stimulation was administered to the left FEF, targeted using F3 of the international 10-20 system. A 4-electrode array for return current was placed circumferentially. Stimulation parameters were optimised using the results from a cohort of healthy control volunteers. A visual TDT task comprising paired flashing lights, previously described [1], was used to measure TDT. This task was performed at baseline, during, and after tDCS stimulation.

Results: Results from four control subjects allowed for optimisation of the stimulation protocol which will be used to compare TDT scores with and without stimulation in an AOPTD cohort. The pilot data collected aligns with our hypothesis.

Conclusion: The optimised protocol for FEF stimulation allows transient modulation of cortical activity and thus provides an opportunity to directly influence attentional orienting at a cortical level and measure the effects on Temporal Discrimination.

References: 1. Bradley D, Whelan R, Kimmich O, et al. Temporal discrimination thresholds in adult-onset primary torsion dystonia: an analysis by task type and by dystonia phenotype. J Neurol. 2011;259(1):77-82. 2. Mc Govern, E. M., Killian, O., Narasimham, S., Quinlivan, B., Butler, J. B., Beck, R., Hutchinson, M. (2017). Disrupted superior collicular activity may reveal cervical dystonia disease pathomechanisms. Scientific Reports, 7(1), 16753. 3. Kanai R, Muggleton N, Walsh V. Transcranial Direct Current Stimulation of the Frontal Eye Fields during Pro- and Antisaccade Tasks. Front Psychiatry. 2012;3:45.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/transcranial-neuromodulation-of-the-frontal-eye-fields-targeting-temporal-discrimination-thresholds-tdt-in-adult-onset-primary-torsion-dystonia-aoptd/