DFG Project: Vestibular-visual-proprioceptive cerebral networks of self-motion perception: Critical investigations on the theory of two pathways
Project Title:
Vestibular-visual-proprioceptive brain networks in self-motion perception: critical tests of the dual pathway theory
Principal Investigators:
Prof. Dr. Mark W. Greenlee and Prof. Dr. Anton L. Beer
Project Members:
Maximilian Back
Project Duration:
01.11.2024 - 31.10.2027
Project Description:
Self-motion perception describes the sensation of head or body movements in space. It is one of the most important perceptual systems in humans and animals alike. Without it, effective navigation through space would not be feasible. Self-motion perception is based on the multisensory integration of vestibular, visual, and proprioceptive signals. Previous research has shown that self-motion perception relies on a relatively large network of cortical and subcortical brain regions that interact with each other. Recently, several models primarily based on animal studies suggested that these distributed brain regions are likely organized along two brainstem-cortical pathways: The posterior-lateral pathway projecting from the vestibular nuclei (VN) via the ventral posterior lateral (VPL) nucleus of the thalamus to brain areas in the lateral cortex and the anterior-medial pathway projecting from the VN via anterior thalamic divisions to the medial cortex. In recent years, several research groups (including the group of the PIs) have successfully characterized the nodes and interactions of the posterior-lateral network in both animals and humans. By contrast, the anterior-medial network is still only poorly understood. In fact, even some relevant brain regions (e.g., the vestibular pericallosal sulcus) of this network have not been identified until recently. Therefore, this brain imaging project aims to investigate the anterior-medial system of self-motion perception and to compare it with the posterior-lateral system. Based on previous research, we tentatively hypothesize that the anteriormedial system is strongly involved in spatial navigation, heading, and locomotion. We further expect that activation within this network is strongly affected by proprioceptive signals (e.g., of the neck muscles). We expect that this system is particularly vulnerable to mechanisms of aging that are associated with (sub-clinical) vestibular-visual impairments. By contrast, we assume that it is less involved in motion sickness than the posterior-lateral system. The project builds on our prior work that has led to several important discoveries concerning the neural basis of self-motion perception in humans. Moreover, it will extend our current knowledge by investigating the dissociation of two cortical vestibular-visual pathways.
Relevant References:
DFG Project: Magnetic Resonance Imaging of Neural Plasticity in the Visual Cortex of Patients with Central Vision Loss: Effects of Long-term Adaptation and Training
Project Title:
Magnetic Resonance Imaging of Neural Plasticity in the Visual Cortex of Patients with Central Vision Loss: Effects of Long-term Adaptation and Training
Principal Investigators:
PD Dr. Tina Plank (Co-investigator: Prof. Dr. Mark W. Greenlee)
Project Members:
Ms. Edith Benkowitsch und Ms. Elena von Perponcher
Project Duration:
01.07.2021 - 31.07.2026
Project Description:
Retinal diseases such as macular degeneration usually lead to central vision loss, making the affected patients dependent on their peripheral residual vision. Often a kind of pseudo fovea (preferred retinal locus, PRL) develops in the peripheral visual field, which is then used in everyday life for the fixation of objects or faces, as well as for reading. These long-term adaptation processes are accompanied by certain neuroplastic changes in the visual cortex of the affected patients. Furthermore, appropriate training protocols, such as visual perceptual learning tasks, can help to further improve peripheral visual performance and even trigger neuronal plasticity. Our goal in this planned project is to investigate how these two neuroplastic processes of long-term adaptation and training act together and to uncover possible interrelations between the two. For this purpose, visual perceptual learning in the peripheral visual field will be applied, and it will be examined to what extent the learning success at the PRL of patients with central vision loss will be different from the learning success at a comparable peripheral site in the opposite visual hemifield (OppPRL) and from the learning success of normally sighted control persons, who are trained in the same visual task. The training measures will be accompanied by (functional) magnetic resonance imaging (fMRI) to reveal the neural correlates of learning in the visual cortex. Additionally, the biochemical changes caused by learning will be determined by magnetic resonance spectroscopy (MRS). To investigate possible changes in the cortical macro- and microstructure in grey and white matter of the visual cortex, structural and diffusion-weighted MRI will be performed. These measures will provide us with a more comprehensive picture of long and short term neuroplastic adaptation processes in patients with central vision loss and thus help to design even more efficient training protocols.
Relevant References:
DFG Project: The neuronal basis of perceptual filling-in
Filling-in is the perceptual tendency of an observer to perceive a continuous visual pattern despite the presence of an intermittent blank region. Filling-in occurs at the blindspot but also in scotomatous regions in patients with diseases of the visual pathways.
Project Title:
The neural computation for perceptual filling-in
Principal Investigators:
Prof. Dr. Mark W. Greenlee in cooperation with Prof. Dr. Chien-Chung Chen (NTU Taipei)
Project Members:
Dr. Yih-Shiuan Lin
Project Duration:
01.07.2022 - 30.06.2025
Project Description:
Filling-in is the perceptual tendency of an observer to perceive a continuous visual pattern despite the presence of an intermittent blank region. Filling-in occurs at the blindspot but also in scotomatous regions in patients with diseases of the visual pathways. Since filling-in occurs in a blank region there is no physical stimulus to elicit a response in any visual mechanisms at that retinotopic location. Observers are usually requested on a given trial to report when they experience filling-in. Neural responses to stimuli with and without filling-in can be compared to determine whether these responses differ on these two trial types. Machine learning can be applied to determine if a classifier can distinguish between these two types of events. With univariate analysis, we found no difference between BOLD activation in the filling-in and no filling-in trials. However, using a leave-one-out training procedure and a support vector machine, it was possible to classify the percepts by the activation pattern differences in early visual cortex (Lin, Greenlee & Chen, 2020). To resolve these issues, we have developed a new paradigm to assess the presence or absence of perceptual filling-in. Observers will be presented periodic patterns with intermittent blank regions, which serve as artificial scotoma. By presenting a target in the blank region after filling-in occurs we can measure the neural response to the target and determine whether this response is affected by the presence of filling-in. The target will be a stimulus that can elicit a large enough neural response to allow for a reliable measurement of neural activity. We will vary the contrast of the target to determine the contrast response function in the presence of the inducer. This allows us to determine the contrast response function to the target. Variations in the physical properties of the inducers and targets will be conducted to separate response components related to the inducer and target stimuli.In a series of three studies, we will parametrically measure the response functions to the target with functional magnetic resonance imaging (fMRI), event related potentials (ERP) and psychophysics experiments. The latter will be conducted to establish the operating range of the basic phenomena. The fMRI experiments will precisely identify the brain areas for filling-in. Such precision is required as the candidate area for filling-in, V2, is small. The ERP experiments will determine the temporal dynamics of the target response with respect to the onset of filling-in. The filling-in phenomenon will be related to other illusions involving border contrast.The results of these studies will be simulated using a computational model of early visual processing. In these models, lateral inhibition and excitation influence the neural mechanisms that respond selectively to target stimuli. In this way, we will be able to develop a new theory of perceptual filling-in using computational modelling.
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