Abstract
Smooth pursuit eye movements (SPEM) are needed to keep the retinal image of slowly moving objects within the fovea. Depending on the task, about 50%–80% of patients with schizophrenia have difficulties in maintaining SPEM. We designed a study that comprised different target velocities as well as testing for internal (extraretinal) guidance of SPEM in the absence of a visual target. We applied event-related fMRI by presenting four velocities (5, 10, 15, 20°/s) both with and without intervals of target blanking. 17 patients and 16 healthy participants were included. Eye movements were registered during scanning sessions. Statistical analysis included mixed ANOVAs and regression analyses of the target velocity on the Blood Oxygen Level Dependency (BOLD) signal. The main effect group and the interaction of velocity×group revealed reduced activation in V5 and putamen but increased activation of cerebellar regions in patients. Regression analysis showed that activation in supplementary eye field, putamen, and cerebellum was not correlated to target velocity in patients in contrast to controls. Furthermore, activation in V5 and in intraparietal sulcus (putative LIP) bilaterally was less strongly correlated to target velocity in patients than controls. Altered correlation of target velocity and neural activation in the cortical network supporting SPEM (V5, SEF, LIP, putamen) implies impaired transformation of the visual motion signal into an adequate motor command in patients. Cerebellar regions seem to be involved in compensatory mechanisms although cerebellar activity in patients was not related to target velocity.
Highlights
Smooth pursuit eye movements (SPEM) are needed to keep slowly moving visual objects within the fovea
This finding suggests that the utilization of the motion signal derived from V5 and its transfer to sensorimotor systems is altered in patients. In another fMRI-study, we found a less strong correlation between the measured pursuit eye velocity and the BOLD-signal (Blood Oxygen Level Dependency) in visual motion processing area V5 in patients compared to healthy participants [10]
The main effect group revealed that activation of V5 bilaterally and right putamen was higher in healthy subjects than in patients whereas the reverse contrast showed that in patients activation within cerebellar vermis was higher than in healthy participants (Figure 1, Table 2)
Summary
Smooth pursuit eye movements (SPEM) are needed to keep slowly moving visual objects within the fovea. The maintenance of smooth pursuit is driven by a combination of retinal and extraretinal mechanisms, with their loadings depending on the extent of experience with the pattern of target motion and the predictability of the stimulus [1]. Despite the fact that pursuit abnormalities in patients have been shown to be stable over time and mostly independent of symptom state and, with some exceptions, independent of medication [5], patient’s SPEM performance highly depends on the task demands. We have recently shown that patient’s SPEM are unimpaired with stimuli that do not require constant dynamic adjustments of pursuit velocity and acceleration as with sinusoidal tasks, or abrupt reversals in target direction as with triangular waveforms [6]. Another study showed that pursuit of even unpredictably moving sinusoidal targets can be performed
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