Measurement & Analysis of the Temporal Discrimination Threshold Applied to Cervical Dystonia
Summary
Methods for the measurement and analysis of the temporal discrimination threshold are presented, and its application to the study of the pathogenesis of cervical dystonia are discussed.
Abstract
The temporal discrimination threshold (TDT) is the shortest time interval at which an observer can discriminate two sequential stimuli as being asynchronous (typically 30-50 ms). It has been shown to be abnormal (prolonged) in neurological disorders, including cervical dystonia, a phenotype of adult onset idiopathic isolated focal dystonia. The TDT is a quantitative measure of the ability to perceive rapid changes in the environment and is considered indicative of the behavior of the visual neurons in the superior colliculus, a key node in covert attentional orienting. This article sets out methods for measuring the TDT (including two hardware options and two modes of stimuli presentation). We also explore two approaches of data analysis and TDT calculation. The application of the assessment of temporal discrimination to the understanding of the pathogenesis of cervical dystonia and adult onset idiopathic isolated focal dystonia is also discussed.
Introduction
Temporal discrimination describes a person's ability to discriminate, or perceive, rapid changes in their environment. The temporal discrimination threshold (TDT) is the shortest time interval at which an individual can perceive that two sequential sensory stimuli are asynchronous. Temporal discrimination has been shown to be abnormally prolonged in disorders affecting the basal ganglia, including dystonia1,2,3,4,5,6,7.
Dystonia is the third most common neurological movement disorder – after Parkinson's disease and Essential Tremor. It is characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive, movements or postures8. Dystonia can affect any part of the body. When it affects one body part it is known as focal dystonia8. Dystonia affecting the neck muscles is known as cervical dystonia, and is the most common phenotype of adult onset idiopathic isolated focal dystonia.9,10 The pathogenesis of cervical dystonia remains unknown; it is considered to be a genetic disorder with autosomal dominant inheritance and markedly reduced penetrance. Environmental factors are also considered important in relation to disease penetrance and expression.
The superior colliculus, a sensorimotor structure situated in the dorsal midbrain, is important for the rapid detection of environmental stimuli in the process of covert attentional orienting2,11,12. Visual stimuli access the superior colliculus rapidly through the retino-tectal magnocellular pathway. The TDT is a simple, objective measure believed to represent the processing of visual (and other sensory stimuli) in the superficial layers of the superior colliculus. The TDT has been studied in individuals with cervical dystonia, their unaffected relatives and healthy control participants. Compared to age- and sex-matched control participants, an abnormal TDT has high sensitivity (97%, 36 of 37 patients) and specificity (98-100%) in cervical dystonia1. An abnormal TDT has been found in 50% of unaffected first-degree female relatives of patients with cervical dystonia (14 of 25, aged 48 years or older), demonstrating age- and sex-related penetrance with autosomal dominant inheritance13,14. An abnormal TDT in unaffected relatives of cervical dystonia patients (compared to relatives with normal TDTs) is associated with increased putaminal volume (by voxel-based morphometry)15 and reduced putaminal activity (by fMRI)4. The superior colliculus is considered a significant node in the neuronal network, which is dysfunctional in cervical dystonia12. The assessment of temporal discrimination is regarded as providing important clues as to the pathomechanisms underlying cervical dystonia.
The goal of this article is to present two methods for measuring and analyzing temporal discrimination, as well as demonstrating the application of this method to studying the pathophysiology of cervical dystonia.
Protocol
Representative Results
Discussion
TDT Measurement and Analysis
Two forms of apparatus (table-top and headset), two methods of stimulus presentation (staircase and random), and two approaches to data analysis (traditional and distribution) have been presented to illustrate how to measure and quantify a person's temporal discrimination ability. The portable headset provides a convenient hardware option that ensures consistency in distance and angles between the participant and the LED light sources while al…
Divulgaciones
The authors have nothing to disclose.
Acknowledgements
This research was supported by grants from the Health Research Board, Dystonia Ireland, Science Foundation Ireland and the Irish Institute for Clinical Neuroscience.
Materials
| TDT head set | Can be supplied by Trinity Centre for Bioengineering, Trinity College Dublin. Alternatively full instructions are available for free download from http://www.dystoniaresearch.ie/temporal-discrimination-threshold/ | 1 | A custom-built, portable device for the presentation of visual stimuli. |
| TDT table top LED box | Can be supplied by Trinity Centre for Bioengineering, Trinity College Dublin. Alternatively full instructions are available for free download from http://www.dystoniaresearch.ie/temporal-discrimination-threshold/ | 2 | A custom-built, table-top device for the presentation of visual stimuli. |
| Microcontroller | Can be supplied by Trinity Centre for Bioengineering, Trinity College Dublin. Alternatively full instructions are available for free download from http://www.dystoniaresearch.ie/temporal-discrimination-threshold/ | 3 | A custom-built microcontroller for the delivery of visual stimuli in staircase or random order, with precise inter-stimulus intervals. |
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