Optometry and Vision Sciences - Theses
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ItemTemporal disintegration: a phenomenological and neurophysiological investigation( 2017)The primary aim of this PhD research programme was to explore the neurophysiological correlates of temporal disintegration. This phenomenon is typified by disturbing anomalies in the normal flow and experience of time, and is a significant co-morbidity in a variety psychiatric illnesses. The research focused on the application of sub-second and supra-second psychophysical methods as well as neuroimaging to explore neural correlates of temporal disintegration. Experiments were conducted with two cohorts: patients with bipolar disorder, and healthy participants who were administered the dissociative agent ketamine. The bipolar disorder study utilised a longitudinal, repeated measures design. The ketamine experiments were randomised, double blind studies with placebo controls. Three main types of measurements were used in the studies. Firstly, questionnaires were administered which measured mood states, dissociative states and temporal disintegration. Secondly, behavioural responses to visual stimuli were measured in two temporal domains: sub-second perceptual ordering, and supra-second perceived duration judgement. Thirdly, during performance of the sub-second task, neuroimaging was conducted: fMRI for participants given ketamine and EEG for patients with bipolar disorder. The sub-second method was adapted from the temporal order judgement task of Morrone et al. [2005]. Participants reported the order of two briefly flashed stimuli presented close to the time that they made an eye movement. In this task, the stimuli may appear to be inverted in temporal order, especially when eye movements coincide with the flashed stimuli. The supra-second method was adapted from the colour-time task of Coull et al. [2004]. It involved judging the relative duration of two successive stimuli that cycled through a range of colours over time. In the bipolar disorder patients, a strong association was found between measures of mood, dissociative symptoms and the phenomenon of temporal dissociation. For the supra-second task, we found lower mood scores (measured by the Bipolar Depression Rating Scale) were associated with a greater number of errors in the time condition than the colour condition. For the sub-second psychophysical tests, the proportion of inverted temporal judgements increased in association with manic symptoms (11% increase for each point increase in Young Mania Rating Scale, p<0.05). Manual reaction times in 2AFC responses to temporal judgements were lengthened by ketamine and in inverted judgements. The fMRI results showed increased BOLD signal for inverted trials bilaterally in the insular/claustral regions and in the anterior cingulate cortex (p<0.001). In inverted trials, temporal disintegration as measured by the Temporal Integration Inventory was correlated with the activity of the left temporoparietal junction (Kendall’s τ = 0.48, p < 0.01). Together, these findings indicate that there is a significant linkage between mood and dissociative states and the phenomenon of temporal disintegration. They also reveal that both sub-second and supra- second timing performance are altered by ketamine induced dissociation and with mood changes in bipolar disorder. The findings provide support for an integrated functional network involved in sub-second temporal processing which includes the claustrum and temporoparietal junctions. These insights are important in that they can inform our understanding of the determinants of temporal disintegration and may also provide insights into the underlying pathology of bipolar disorder.