| Summary: | Observing body related abnormalities such as broken limbs (like fingers) can lead to a vicarious somatosensory experience. Such responses depend on a complex interaction between different brain regions in order to give rise to a somatosensory experience based on visual stimulation alone. In this thesis, I use multiple imaging techniques to demonstrate this is an example of embodied simulation, an ingrained ability of the brain that allows an observer to simulate others’ experiences based on somatosensory and lateral occipital involvement.
In the first stages of my PhD project I developed a novel procedure where realistic computer-generated 3D models of subjects’ actual hands were created, and then tested their suitability for the neuroimaging experiments in this thesis. After finding the models suitable, I created images of salient hands with finger abnormalities, resembling broken fingers, in order to elicit a strong vicarious response. To investigate whether this response elicits somatosensory activity, I used 7T fMRI in combination with a highly specific tactile localiser to describe the involvement of different sub-regions of the S1 hand-area in the observation of distorted finger postures. Among the sub-regions distortion-related activation was the strongest in posterior regions of the S1 (BA 2). This was followed by two EEG experiments which investigated the involvement of the lateral occipital cortex in the processing of the observed finger abnormalities. This was assessed using the N1 ERP component, and larger amplitudes to the observation of distorted finger postures were found when compared to control conditions. Lastly, I used MEG to merge the findings made in the previous experiments. For the observation of distorted fingers compared to controls, the results of the MEG experiment revealed a complex temporal evolution: First, involving the visual areas; and then followed by sustained activity of ventral temporal areas in parity with involvement of somatosensory integration areas at later latencies.
This thesis describes with very good spatial and temporal resolution, the neural structures that support the observation of abnormal finger postures. It expands previous literature by showing primary somatosensory responses to body related visual stimuli alone. It demonstrates that the visual body processing areas may initiate the mechanism for embodied simulation. And, it outlines the progression of activation from the visual areas to the somatosensory ones, creating the embodied simulation network.
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