Article

Cerebellar contributions to the processing of saccadic errors

Department of Neuroscience, Erasmus MC, Rotterdam 3000 CA, The Netherlands.
The Cerebellum (Impact Factor: 2.86). 06/2009; 8(3):403-15. DOI: 10.1007/s12311-009-0116-6
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ABSTRACT Saccades are fast eye movements that direct the point of regard to a target in the visual field. Repeated post-saccadic visual errors can induce modifications of the amplitude of these saccades, a process known as saccadic adaptation. Two experiments using the same paradigm were performed to study the involvement of the cerebrum and the cerebellum in the processing of saccadic errors using functional magnetic resonance imaging and in-scanner eye movement recordings. In the first active condition, saccadic adaptation was prevented using a condition in which the saccadic target was shifted to a variable position during the saccade towards it. This condition induced random saccadic errors as opposed to the second active condition in which the saccadic target was not shifted. In the baseline condition, subjects looked at a stationary dot. Both active conditions compared with baseline evoked activation in the expected saccade-related regions using a stringent statistical threshold [the frontal and parietal eye fields, primary visual area, MT/V5, and the precuneus (V6) in the cerebrum; vermis VI-VII; and lobule VI in the cerebellum, known as the oculomotor vermis). In the direct comparison between the two active conditions, significantly more cerebellar activation (vermis VIII, lobules VIII-X, left lobule VIIb) was observed with random saccadic errors (using a more relaxed statistical threshold). These results suggest a possible role for areas outside the oculomotor vermis of the cerebellum in the processing of saccadic errors. Future studies of these areas with, e.g., electrophysiological recordings, may reveal the nature of the error signals that drive the amplitude modification of saccadic eye movements.

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    • "Several studies support that the parietal lobe modulates its activity for saccadic [25], [26], [27] and disparity (the input to vergence) [28], [29] stimulation. The cerebellum has also been implicated in error processing for motor learning for both saccadic [30], [31], [32] and vergence [33], [34], [35] movements. "
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    • "Recent studies have also implicated the cerebellar hemispheres in ocular motor learning. For example, fMRI studies show that the hemispheric lobules VIII–X are active in processing of saccadic errors (van Broekhoven et al., 2009), and TMS over the hemispheric lobule Crus I has a dual effect on saccadic plasticity; potentiating adaptive lengthening and depressing adaptive shortening of saccade amplitudes (Panouilleres et al., 2011). There is also evidence for involvement of the cerebellar hemispheres in adaptation for more voluntary, internally generated saccades such as memory-guided saccades, as opposed to the OMV involvement in more reflexive, visually guided saccades (Nitschke et al., 2004; Alahyane et al., 2008; Kojima et al., 2010b). "
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    • "They found activation in the oculomotor cerebellar vermis (lobules VI and VII) with an ipsilateral preponderance on the side to which the saccadic displacement was adapted. To separate the motor adaptation from the processes related to the visual error, Van Broekhoven et al. [166] employed a paradigm with a random intrasaccadic target step. Random intrasaccadic target steps do induce a postsaccadic visual error, but they do not lead to a gradual change in saccadic amplitudes. "
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