Objective: Analysis of thalamic lesion-induced deficits on oculomotor and reaching behaviour: a psychophysical and fMRI study

Background: Lesion studies and cortical connectivity suggest that higher-order thalamic nuclei such as the mediodorsal thalamus (MD) and the Pulvinar are critical for the selection and monitoring of visually guided movements (1–5). However, which information is contributed by different thalamic nuclei and their impact on cortical circuits is poorly understood.

Methods: We studied 13 patients with focal thalamic lesions (7 left, 3 right and 3 bilateral) with saccade and reach-grasp tasks involving different levels of spatial choices. Lesions in our sample predominantly affected the lateral (VPL, VPM, VL), medial (MD, CL) and posterior (Pulvinar) portions of the thalamus. In a subset of patients (N = 8) we conducted memory saccade tasks to instructed or chosen spatial locations with concurrent event-related fMRI. Patient data in each task condition was compared to 9-20 healthy subjects.

Results: On the group level, saccade amplitudes to the contralesional visual field were significantly smaller than in controls, while saccade latencies and spatial choices did not differ significantly. In the single patient analysis, patients with a right, but not with left or bilateral pulvinar lesions exhibited an ipsilesional bias in the free saccade choice condition. Patients with medial thalamus damage did not exhibit a spatial choice bias but hypometric saccades towards the contralesional hemifield. Reach and grasp deficits were observed in four of the patients without a clear lesion pattern. The main functional effect of the thalamic lesions on remote brain regions consisted of a bilateral increase of BOLD activity in frontal cortices accompanied by a bilateral reduction of activity in the intraparietal sulcus during spatial cue presentation in either hemifield.

Conclusions: Taken together, these results suggest differing functional roles of thalamic nuclei on visually guided eye and hand movements: MD being involved in saccade planning/execution while Pulvinar being more important for the selection of saccade goals. Our fMRI results suggest that removing thalamic input leads to over-activity in frontal cortices, which can be interpreted either as disinhibition or compensation due to increased task effort. The bilateral decrease of BOLD activity in the intraparietal sulcus might partly account for the hypometric saccades and the spatial choice deficits.

References: 1. Wilke, M., Turchi, J., Smith, K., Mishkin, M. & Leopold, D. A. Pulvinar Inactivation Disrupts Selection of Movement Plans. J. Neuroscience. 30, 8650–8659 (2010). 2. Dominguez-Vargas, A.-U., Schneider, L., Wilke, M.* & Kagan, I.* Electrical Microstimulation of the Pulvinar Biases Saccade Choices and Reaction Times in a Time-Dependent Manner. J. Neuroscience. 37, 2234–2257 (2017). 3. Wilke, M. et al. Reach and grasp deficits following damage to the dorsal pulvinar. Cortex. 99, 135–149 (2018). 4. Benarroch, E. E. Pulvinar Associative role in cortical function and clinical correlations. Neurology 84, 738–747 (2015). 5. Crapse, T. B. & Sommer, M. A. Corollary discharge circuits in the primate brain. Curr. Opin. Neurobiol. 18, 552–557 (2008).

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-impact-of-thalamic-lesions-on-visuomotor-behavior-a-behavioral-and-fmri-study/