Predictive smooth eye pursuit in a population of young men: II. Effects of schizotypy, anxiety and depression

Cognition and Action Group, Neurology Department, Medical School, Aeginition Hospital, National and Kapodistrian University of Athens, Athens, Greece.
Experimental Brain Research (Impact Factor: 2.04). 12/2011; 215(3-4):219-26. DOI: 10.1007/s00221-011-2888-4
Source: PubMed


Smooth pursuit eye movement dysfunction is considered to be a valid schizophrenia endophenotype. Recent studies have tried to refine the phenotype in order to identify the specific neurophysiological deficits associated with schizophrenia. We used a variation of the smooth eye pursuit paradigm, during which the moving target is occluded for a short period of time and subjects are asked to continue tracking. This is designed to isolate the predictive processes that drive the extraretinal signal, a process previously reported to be defective in schizophrenia patients as well as their healthy relatives. In the current study, we investigated the relationship between predictive pursuit performance indices and age, education, non-verbal IQ, schizotypy and state anxiety, depression in 795 young Greek military conscripts. State anxiety was related to better predictive pursuit performance (increase in residual pursuit gain), while disorganized schizotypy was related to deficient predictive pursuit performance (decreased residual gain). This effect was independent of the effect of disorganized schizotypy on other oculomotor functions supporting the hypothesis that predictive pursuit might be specifically affected in schizophrenia spectrum disorders and could be considered as a distinct oculomotor endophenotype.

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Available from: Dimitrios Avramopoulos, Jan 14, 2014
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    • "Our specific hypothesis, based on previous studies, was that predictive pursuit would be correlated with visually guided pursuit but also with other oculomotor and cognitive tasks, engaging prefrontal functions such as the antisaccade, working memory and sustained attention tasks. In the companion paper (Kattoulas et al. 2011), we will investigate possible relationship of performance in this task with psychometric tests included in the ASPIS study. "
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    ABSTRACT: Smooth eye pursuit is believed to involve the integration of an extraretinal signal formed by an internal representation of the moving target and a retinal signal using the visual feedback to evaluate performance. A variation of the smooth eye pursuit paradigm (in which the moving target is occluded for a short period of time and subjects are asked to continue tracking) designed to isolate the predictive processes that drive the extraretinal signal was performed by 1,187 young men. The latency to the onset of change in pursuit speed, the time of decelerating eye-movement speed and the steady state residual gain were measured for each subject and correlated with measures of other oculomotor (closed-loop smooth eye pursuit, saccade, antisaccade, active fixation) and cognitive tasks (measuring sustained attention and working memory). Deceleration time increased with increasing age, while education, general IQ and cognitive variables had no effect on predictive pursuit performance. Predictive pursuit indices were correlated to those of closed-loop pursuit and antisaccade performance, but these correlations were very weak except for a positive correlation of residual gain to saccade frequency in the fixation task with distracters. This correlation suggested that the maintenance of active fixation is negatively correlated with the ability to maintain predictive pursuit speed. In conclusion, this study presents predictive pursuit performance in a large sample of apparently healthy individuals. Surprisingly, predictive pursuit was weakly if at all related to closed-loop pursuit or other oculomotor and cognitive tasks, supporting the usefulness of this phenotype in the study of frontal lobe integrity in normal and patient populations.
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    ABSTRACT: This paper introduces a model of oculomotor control during the smooth pursuit of occluded visual targets. This model is based upon active inference, in which subjects try to minimise their (proprioceptive) prediction error based upon posterior beliefs about the hidden causes of their (exteroceptive) sensory input. Our model appeals to a single principle - the minimisation of variational free energy - to provide Bayes optimal solutions to the smooth pursuit problem. However, it tries to accommodate the cardinal features of smooth pursuit of partially occluded targets that have been observed empirically in normal subjects and schizophrenia. Specifically, we account for the ability of normal subjects to anticipate periodic target trajectories and emit pre-emptive smooth pursuit eye movements - prior to the emergence of a target from behind an occluder. Furthermore, we show that a single deficit in the postsynaptic gain of prediction error units (encoding the precision of posterior beliefs) can account for several features of smooth pursuit in schizophrenia: namely, a reduction in motor gain and anticipatory eye movements during visual occlusion, a paradoxical improvement in tracking unpredicted deviations from target trajectories and a failure to recognise and exploit regularities in the periodic motion of visual targets. This model will form the basis of subsequent (dynamic causal) models of empirical eye tracking measurements, which we hope to validate, using psychopharmacology and studies of schizophrenia.
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