Abstract
Temporal discrimination is the ability to determine that two sequential sensory stimuli are separated in time. For any individual, the temporal discrimination threshold (TDT) is the minimum interval at which paired sequential stimuli are perceived as being asynchronous; this can be assessed, with high test–retest and inter-rater reliability, using a simple psychophysical test. Temporal discrimination is disordered in a number of basal ganglia diseases including adult-onset dystonia, of which the two most common phenotypes are cervical dystonia and blepharospasm. The causes of adult-onset focal dystonia are unknown; genetic, epigenetic, and environmental factors are relevant. Abnormal TDTs in adult-onset dystonia are associated with structural and neurophysiological changes considered to reflect defective inhibitory interneuronal processing within a network which includes the superior colliculus, basal ganglia, and primary somatosensory cortex. It is hypothesized that abnormal temporal discrimination is a mediational endophenotype and, when present in unaffected relatives of patients with adult-onset dystonia, indicates non-manifesting gene carriage. Using the mediational endophenotype concept, etiological factors in adult-onset dystonia may be examined including (i) the role of environmental exposures in disease penetrance and expression; (ii) sexual dimorphism in sex ratios at age of onset; (iii) the pathogenesis of non-motor symptoms of adult-onset dystonia; and (iv) subcortical mechanisms in disease pathogenesis.
Highlights
Specialty section: This article was submitted to Movement Disorders, a section of the journal Frontiers in Neurology
Temporal discrimination is disordered in a number of basal ganglia diseases including adult-onset dystonia, of which the two most common phenotypes are cervical dystonia and blepharospasm
It is hypothesized that abnormal temporal discrimination is a mediational endophenotype and, when present in unaffected relatives of patients with adult-onset dystonia, indicates non-manifesting gene carriage
Summary
Age-Related Effects An early study of 80 healthy volunteers aged from 18 to 82 years found that TDT increased only in subjects older than 65 years [6]. Healthy musicians exhibited less age-related decline in temporal discrimination than non-musicians, suggesting some protective effect associated with playing an instrument. This finding is supported by a study which showed that a moderate amount (4–14 years) of music training early in life was associated with faster neural timing in response to speech later in life, even long after training had stopped [13]. Sub-second temporal processing of sensory information has been studied by several methodological approaches including temporal order judgment (TOJ), frequency discrimination task, time estimation tasks, and interval discrimination tasks [14,15,16] These various tasks differ from TDT in the neural circuits activated during the experimental procedure. The TDT seems to be a perceptive threshold uninfluenced by memory formation [1, 21] and at the interval used, in the tens of milliseconds range, is beyond cognitive control [22]
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