Slowed luminance reaction times in cervical dystonia: disordered superior colliculus processing

Background: Abnormal temporal discrimination in cervical dystonia is hypothesised to be due to disrupted processing in the superior colliculus. The fast, luminance-based, retino-tectal pathway, projects to the superior colliculus; chromatic stimuli responses, via the retino-geniculo-calcarine pathway, are up to 30ms longer. Methods: In 20 cervical dystonia and 20 age-matched control participants, we compared reaction times to two flashing visual stimuli: (i) a chromatic annulus and (ii) a luminant, non-coloured annulus. Participants pressed a joystick control when they perceived the annulus flashing. Results: Reaction times in control participants were 20ms significantly faster in the luminant condition than the chromatic (p= 0.017). Patients with cervical dystonia had no reaction time advantage in response to the luminant stimulus. Conclusion: Cervical dystonia patients (compared to control participants) demonstrated no reduction in their reaction time to luminant stimuli, processed through the retino-tectal pathway. This finding is consistent with superior colliculus dysfunction in cervical dystonia

Neural Correlates of Abnormal Temporal Discrimination in Unaffected Relatives of Cervical Dystonia Patients

Background: An abnormal temporal discrimination threshold in cervical dystonia (CD) is considered to be a mediational endophenotype; in unaffected relatives it is hypothesized to indicate non-manifesting gene carriage. The pathogenesis underlying this condition remains unknown. Investigation of the neural networks involved in disordered temporal discrimination may highlight its pathomechanisms.Objective: To examine resting state brain function in unaffected relatives of CD patients with normal and abnormal temporal discrimination. We hypothesized that the endophenotype, an abnormal temporal discrimination, would manifest as altered connectivity in relatives in regions associated with CD, thereby illuminating the neural substrates of the link between temporal discrimination and CD.Methods: Rs-fMRI data was analyzed from two sex- and age-matched cohorts: 16 unaffected relatives of CD patients with normal temporal discrimination and 16 with abnormal temporal discrimination. Regional and whole brain functional connectivity measures were extracted via Independent Component Analysis (ICA), Regional Homogeneity (ReHo), and Amplitude of Low Frequency (ALFF) analyses.Results: Our ICA analysis revealed increased connectivity within both the executive control and cerebellar networks and decreased connectivity within the sensorimotor network in relatives with abnormal temporal discrimination when compared to relatives with normal temporal discrimination. The ReHo and ALFF analyses complimented these results and demonstrated connectivity differences in areas corresponding to motor planning, movement coordination, visual information processing, and eye movements in unaffected relatives with abnormal temporal discrimination.Conclusion: Disordered connectivity in unaffected relatives with abnormal temporal discrimination illuminates neural substrates underlying endophenotype expression and supports the hypothesis that genetically determined aberrant connectivity, when later coupled with unknown environmental triggers, may lead to disease penetrance

A comprehensive investigation of negative visitor behaviour in the zoo setting and captive animals' behavioural response

Negative visitor behaviour in zoos such as banging, shouting and feeding animals are unwanted, but under-studied, visitor actions. It is not known how prevalent negative behaviour is, which species or enclosure type receives the most negative behaviour or how these behaviours affect zoo-housed animals. In this study, a comprehensive assessment of negative visitor behaviour, using an innovative methodology, was conducted at 25 different enclosures at Fota Wildlife Park, Ireland. Additionally, animal activity level and out of sight behaviour was observed. Descriptive statistics and general linear models were used to investigate which variables affected behaviour. Banging was the most common negative behaviour, while Humboldt penguins, lion-tailed macaques and Sumatran tigers were the most harassed species. Negative actions increased as visitor number increased and at traditional-style viewing areas. Active animal behaviour and out of sight animals were effected as negative visitor behaviours increased, but there appeared to be a tolerance threshold before a behavioural response was observed. By understanding negative behaviours, zoos can strive to reduce them and promote positive animal welfare

Temporal Discrimination: Mechanisms and Relevance to Adult-Onset Dystonia

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

Young Women do it Better: Sexual Dimorphism in Temporal Discrimination

The temporal discrimination threshold (TDT) is the shortest time interval at which two sensory stimuli presented sequentially are detected as asynchronous by the observer. TDTs are known to increase with age. Having previously observed shorter thresholds in young women than in men, in this work we sought to systematically examine the effect of sex and age on temporal discrimination. The aims of this study were to examine, in a large group of men and women aged 20–65 years, the distribution of TDTs with an analysis of the individual participant’s responses, assessing the 'point of subjective equality' and the 'just noticeable difference' (JND). These respectively assess sensitivity and accuracy of an individual’s response. In 175 participants (88 women) aged 20–65 years, temporal discrimination was faster in women than in men under the age of 40 years by a mean of approximately 13 ms. However, age-related decline in temporal discrimination was three times faster in women so that, in the age group of 40–65 years, the female superiority was reversed. The point of subjective equality showed a similar advantage in younger women and more marked age-related decline in women than men, as the TDT. JND values declined equally in both sexes, showing no sexual dimorphism. This observed sexual dimorphism in temporal discrimination is important for both (a) future clinical research assessing disordered mid-brain covert attention in basal-ganglia disorders, and (b) understanding the biology of this sexual dimorphism which may be genetic or hormonal.Health Research BoardDystonia IrelandIrish Institute for Clinical NeuroscienceFoundation for Dystonia Research (Belgium