Eye, hand and space representations and causal interference in bihemispheric pulvinar-parietal circuitry

by Danial Arabali
Doctoral thesis
Date of Examination:2018-06-14
Date of issue:2019-05-29
Advisor:Dr. Igor Kagan
Referee:Prof. Dr. Melanie Wilke
Referee:Prof. Hansjörg Scherberger
Referee:Prof. Dr. Alexander Gail
Referee:Dr. Arezoo Pooresmaeili
Referee:Prof. Dr. Annekathrin Schacht
Persistent Address: http://dx.doi.org/10.53846/goediss-7473

 

 

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Abstract

English

Recent research proposes that a proper action is the outcome of continuous competition between multiple frontoparietal neuronal representations of possible response options and this competition is biased by the input from other cortical or subcortical regions within and across two hemispheres. Pulvinar, the largest thalamic nucleus that has vast and complex connections with many cortical areas, is one likely candidate for having influence on action selection and specification. It is reciprocally connected with frontoparietal areas related to visually-guided eye and arm movements and its lesions cause deficits partially similar to what was observed after parietal lesions, such as spatial neglect and optic ataxia. In spite of that the information about how exactly pulvinar encodes visually-guided eye and arm motor goals and actions is very scarce. During the last few years we tried to understand the role of pulvinar in goal-directed visuomotor behavior. We compared the neuronal representations of spatial movements with eye, left or right arm in parietal cortex and dorsal part of pulvinar while monkeys performed different visuomotor tasks. In addition, we investigated the causal role of pulvinar in modulating these neuronal representations in parietal cortex by pharmacologically inactivating pulvinar in one hemisphere and simultaneously recording from parietal reach- or saccade-related areas from both hemispheres. Taken together our findings show that neuronal signals in dorsal pulvinar encode spatial as well as effector information during visual processing, motor planning and execution with considerable similarities to parietal cortex. In addition, pulvinar is causally involved in parietal action selection mechanism since its unilateral inactivation not only causes space- and limb-specific behavioral deficits but also strongly modulates the neuronal responses, as well as intraand inter-areal communication underlying visually-guided reaches and saccades in both hemispheres. Although much remains to be elucidated, both in regard to detailed properties of neuronal encoding in the dorsal pulvinar as compared to parietal cortex, and in terms of epoch- and tuning-specific effects of pulvinar inactivation, this work demonstrates that the dorsal pulvinar and parietal cortex are tightly linked functionally. Furthermore, it seems that pulvinar might be more strongly involved in mediating visually-guided reach signals than saccades, underscoring its putative role in coordinated visually-guided actions which are one of the hallmarks of behavioral repertoire in primates.
Keywords: visually-guided eye and arm movements; goal-directed behavior; parietal cortex; dorsal pulvinar; neuronal representations; pulvinar-parietal interactions; intra- and inter-hemispheric communication; pharmacological inactivation
 
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