Control of primate prehension in space and time
by Reinhard Stefan Greulich
Date of Examination:2021-03-19
Date of issue:2021-05-11
Advisor:Prof. Dr. Hansjörg Scherberger
Referee:Prof. Dr. Hansjörg Scherberger
Referee:Dr. Igor Kagan
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Abstract
English
Prehension in primates allows diverse interactions with the environment. It can be separated into two processes: the transport of the arm to the object, termed reach, and the getting hold and manipulation of the object, termed grasp. There is ongoing debate if and how both processes are controlled separately or together by two brain networks, called the dorso-medial and dorso-ventral streams. In this thesis, two experiments examine this question in detail. The first utilizes macaque resting state functional magnetic resonance imaging and examines the functional connectivity of areas of both streams. The second examines the encoding of reach and grasp in humans with functional magnetic resonance imaging and multi voxel pattern analysis utilising cvMANOVA. To enable the second experiment, a 3D printed, MRI-compatible, modular manipulandum was designed. The flexibility of this manipulandum allows for further experimental examination of hand and arm actions in both humans and macaques. Additionally, prehension requires not only control in space but also in time. For a motor action to be meaningful, it has to be initiated at the right time. The second experiment examines the question of how the brain manages this timely initiation in humans by comparing a predictable with an unpredictable go-cue. The results provide further evidence for the two-stream hypothesis. Functional connectivity in lightly anesthetized macaques demonstrates a clear separation between both networks. In humans, we observe individual areas encoding either reach or grasp without overlap. The postcentral gyrus shows grasp encoding and the supraparietal lobule shows reach encoding. Only a few voxels in the postcentral sulcus show an interaction effect. The initiation shows significant encoding in the supplementary motor area, confirming previous research into time interval representation in the brain. Additionally, we see widespread clusters in the premotor and ipsilateral primary motor cortex. A new hypothesis regarding motor initiation is formulated. In conclusion, this thesis provides further support for the two-stream hypothesis, insights into the initiation of prehension movements in humans, and presents a novel manipulandum to investigate prehension actions.
Keywords: fMRI; MVPA; prehension; motor control; neuroscience; 3D print; sensorimotor processing; open source; cvMANOVA; motor initiation