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Heidi Patterson, Ian Erkelens, Claudia Martin Calderon, William Bobier, Benjamin Thompson; Modulation of oculomotor control & adaptation with cerebellar TMS: effects on slow-tonic vergence adaptation.. Journal of Vision 2017;17(10):161. doi: https://doi.org/10.1167/17.10.161.
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© ARVO (1962-2015); The Authors (2016-present)
The adaptation of heterophoria to horizontal base-out prism reflects a slow change in the underlying tonic vergence neural innervation. Recent fMRI evidence suggests the posterior cerebellum may play a role in this unique adaptive process. We applied continuous theta-bust stimulation (cTBS) to the oculomotor vermis (OMV) of the posterior cerebellum to investigate a causal relationship between this neural structure and slow-tonic vergence (STV) adaptation. 14 subjects fused a 0.18 LogMAR chart at 40cm through a 15 prism diopter (PD) base-out prism for 4 minutes after receiving active or sham cTBS stimulation (3-50Hz pulses at 200ms intervals for 40 seconds) to the OMV over the posterior cerebellum. Change in heterophoria, measured with Modified Thornington Technique every 15 seconds, defined the amplitude and rate of STV adaptation. cTBS was applied at 80% of the individual's active motor threshold via a 2x75mm butterfly coil. Stimulation sites were localized using the BrainSight® neuro-navigation system and anatomical landmarks. The amplitude of STV adaptation was not different between active (6.31 ± 0.40 PD) and sham (6.97 ± 0.41 PD) conditions, p = 0.18. There was also no difference between the maximum rate of tonic vergence adaptation in the active (0.41 ± 0.07 PD/s) or sham (0.33 ± 0.05 PD/s) conditions, p = 0.18. Baseline levels of tonic vergence innervation, measured before and after stimulation at each visit, were not different between conditions (p > 0.15). cTBS applied to the OMV of the posterior cerebellum did not affect tonic vergence innervation or STV adaptation to base-out prism in healthy controls. This is in contrast to other types of oculomotor adaptation, where cTBS has been shown to affect both reflexive pro-saccade generation and adaptation to double step stimuli. These results suggest the OMV of the posterior cerebellum plays a limited role in the management and adaptation of tonic vergence neural innervation.
Meeting abstract presented at VSS 2017
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