Same same but different: plasticity of a 'conserved' reflex

Forsthofer, Michael Josef Stefan (2023): Same same but different: plasticity of a 'conserved' reflex. Dissertation, LMU München: Graduate School of Systemic Neurosciences (GSN)

Abstract

Transformation of sensory percepts into motor output form a core element of how any animal interacts with their environment. While some such sensorimotor transformations can be very elaborate and depend on the lifestyle of a species, others serve basic functions and are ubiquitous across vertebrates. Among the latter ones are gaze-stabilizing reflexes, which serve to maintain stable vision during head motion through compensatory eye movements. Despite this conservation throughout evolution, these reflexive behaviors must remain plastic depending on context or past experience to maintain functionality after e.g. impairments of motor or sensory systems through compensation, or to changes in the environment through adaptation. In this thesis, I employ tadpoles of the frog Xenopus laevis to investigate how neuronal circuits contribute to either adaptive or compensatory plasticity on otherwise conserved gaze-stabilizing reflexes. My first study centers on the role of bilateral visual pathways in the development of the optokinetic reflex (OKR). In early embryos, I unilaterally remove the precursor of the eye, the optic vesicle. Tadpoles that develop under such monocular conditions display pathfinding errors of retinal ganglion cells at the optic chiasm. Tadpoles with near normal contralateral projections functionally compensate for the loss of one eye and show consistent responses to both leftward and rightward moving stimuli. In animals with an induced aberrant ipsilateral projection, compensation is increasingly impaired with more pathfinding errors. Combined, this study shows that binocular eyes are required for appropriate visual circuit formation, and that resulting anatomical aberrations impose limitations on compensatory plasticity. In my second study I focus on the role of the cerebellum in plasticity. Combinations of prolonged, repetitive stimulation with lesions of the cerebellum revealed adaptive plasticity of the OKR, where initially very variable OKR responses converge towards a homeostatic motor output by selective increase and decrease of response magnitude. The cerebellum is specifically associated only with response increases, and only starts to exert this influence well after initial OKR onset. This study therefore shows that multiple brain areas differentially contribute to plasticity of eye movements, leading to heterogenous appearance of different modes of plasticity throughout development. Combined, these studies contribute to the understanding of development and purpose of plasticity in Xenopus OKR. Multiple brain areas are involved with plasticity, and their formation depends on canonical, bilateral visual input. Once functional, plasticity mechanisms serve to maintain homeostasis of the OKR response in response to both adaptation and compensation.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: Vision, Gaze-stabilization, Plasticity, Xenopus, Monocular, Training
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 570 Biowissenschaften, Biologie
• Fakultäten: Graduate School of Systemic Neurosciences (GSN)
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 23. Oktober 2023
• 1. Bericht­erstatter:in: Portugues, Ruben