Objective: To deconstruct the temporal discrimination threshold (TDT) into its constituent parts.

Background: The TDT, the shortest detectable interval between two stimuli, has repeatedly been found to be elevated across subtypes of isolated dystonia. This has led to much speculation on how mechanisms underpinning abnormal thresholds may relate to the neurobiology of dystonia. Current paradigms are highly effective at capturing a difference between controls and patients but the threshold value is a composite metric which reflects multiple aspects of sensory processing and inherent decision-making components.

Methods: Twenty-two subjects with cervical dystonia (CD) and an equal number of controls were tested with two novel tasks. Temporal resolution was a randomised and automatic version of existing TDT paradigms with potentially confounding elements removed. Interval discrimination, examined the ability of subjects to compare the length of consecutive intervals in the millisecond range. Both response accuracy and reaction time were recorded.

Results: In the temporal resolution task patients were equally able to classify one- and two-stimulus. Furthermore the ability to compare the length of two consecutive intervals was comparable between groups. Subjects with CD were however slower and more variable in their response times in the temporal resolution task. Modelling data using the drift diffusion model revealed that the decision threshold may be increased in CD such that they required greater evidence before a decision was made.

Conclusions: Temporal processing in the millisecond range may be intact in CD marking a substantial departure form current theories which link timing mechanisms to its pathophysiology. The finding that decision-making strategy is more cautious in this patient group may provide the first tentative link between the neuropsychiatric profile associated with CD and documented sensory abnormalities. It is only recently that the sensory aspects of movement disorders have been championed. Current paradigms have limited ability to discretely probe the range of cognitive and sensory processes involved and the lack of disease specific abnormalities advocates the need for further research in this field. Novel methods and analysis, such as those detailed in this study, will provide the researcher with better tools to quantify precise deficits with ensuing insight into the pathophysiology of dystonia and other movement disorders.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/mind-the-gap-temporal-discrimination-and-cervical-dystonia/