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Empirical object recognition research indicates that objects are represented and perceived as hierarchical part-whole arrangements that vary according to bottom-up and top-down biases. An ongoing debate within object recognition research concerns whether local or global image properties are more fundamental for the perception of objects. Similarly, there is also disagreement about whether the visual system is guided by holistic or analytical processes. Neuroimaging findings have revealed functional distinctions between low and higher-level visual processes across lateral occipital-temporal cortex (LOC), primary visual cortices (V1/V2) and ventral occipital-temporal cortex. Recent studies suggest activations in these object recognition areas and others, such as the fusiform face area (FFA) and extra-striate body area (EBA), are collinear with activations associated with the perception scenes and buildings. Together, this information warrants the focus of the proposed study: to investigate the neural correlates of object recognition and perceived size. During the experiment subjects tracked a fixation stimulus while simultaneously being presented with images of shape contours and faces. Contours and face stimuli subtended small, medium and large visual angles in order to evaluate variance in neural activation across perceived size. In the present study visual areas were hypothesized to modulate as a function of visual angle, meaning that the part-whole relationships of objects vary with their perceived size. / Master of Science

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This thesis describes the development, implementation and application of various quantitative functional magnetic resonance imaging (fMRI) approaches at ultra-high magnetic field including the assessment with regards to applicability and reproducibility. Functional MRI (fMRI) commonly uses the blood oxygenation level dependent (BOLD) contrast to detect functionally induced changes in the oxy-deoxyhaemoglobin composition of blood which reflect cerebral neural activity. As these blood oxygenation changes do not only occur at the activation site but also downstream in the draining veins, the spatial specificity of the BOLD signal is limited. Therefore, the focus has moved towards more quantitative fMRI approaches such as arterial spin labelling (ASL), vascular space occupancy (VASO) or calibrated fMRI which measure quantifiable physiologically and physically relevant parameters such as cerebral blood flow (CBF), cerebral blood volume (CBV) or cerebral metabolic rate of oxygen (CMRO2), respectively. In this thesis a novel MRI technique was introduced which allowed the simultaneous acquisition of multiple physiological parameters in order to beneficially utilise their spatial and temporal characteristics. The advantages of ultra-high magnetic field were utilised to achieve higher signal-to-noise and contrast-to-noise ratios compared to lower field strengths. This technique was successfully used to study the spatial and temporal characteristics of CBV, CBF and BOLD in the visual cortex. This technique is the first one that allows simultaneous acquisition of CBV, CBF and BOLD weighted fMRI signals in the human brain at 7 Tesla. Additionally, this thesis presented a calibrated fMRI technique which allowed the quantitative estimation of changes in cerebral oxygen metabolism at ultra-high field. CMRO2 reflects the amount of thermodynamic work due to neural activity and is therefore a significant physical measure in neuroscience. The calibrated fMRI approach presented in this thesis was optimised for the use at ultra-high field by adjusting the MRI parameters as well as implementing a specifically designed radio-frequency (RF) pulse. A biophysical model was used to calibrate the fMRI data based on the simultaneous acquisition of BOLD and CBF weighted MRI signals during a gas-breathing challenge. The reproducibility was assessed across multiple brain regions and compared to that of various physiologically relevant parameters. The results indicate that the degree of intra-subject variation for calibrated fMRI is lower than for the classic BOLD contrast or ASL. Consequently, calibrated fMRI is a viable alternative to classic fMRI contrasts with regards to spatial specificity as well as functional reproducibility. This calibrated fMRI approach was also compared to a novel direct calibration technique which relies on complete venous oxygenation saturation during the calibration scan via a gas-breathing challenge. This thesis introduced several reliable quantitative fMRI approaches at 7 Tesla and the results presented are a step forward to the wider application of quantitative fMRI.

The aim of this diploma thesis is real-time fMRI neurofeedback. In this case, the activity of amygdala is monitored and controled by an emotional regulatory visual task. A procedure to process measured data online and to incorporate it into the stimulus protocol has been proposed. A pilot study was carried out. Offline analysis of measured data was performed, including evaluation of the results of the analysis. The data is processed in MATLAB using the functions of the SPM library.

Spatio-temporal data have become increasingly prevalent and important for both science and enterprises. Such data are typically embedded in a grid with a resolution larger than the true dimensionality of the underlying system. One major task is to identify the distinct semi-autonomous functional components of the spatio-temporal system and to infer their interconnections. In this thesis, we propose two methods that identify the functional components of a spatio-temporal system. Next, an edge inference process identifies the possibly lagged and weighted connections between the system’s components. The weight of an edge accounts for the magnitude of the interaction between two components; the lag associated with each edge accounts for the temporal ordering of these interactions. The first method, geo-Cluster, infers the spatial components as “areas”; spatially contiguous, non-overlapping, sets of grid cells satisfying a homogeneity constraint in terms of their average pair-wise cross-correlation. However, in real physical systems the underlying physical components might overlap. To this end we also propose δ-MAPS, a method that first identifies the epicenters of activity of the functional components of the system and then creates domains – spatially contiguous, possibly overlapping, sets of grid cells that satisfy the same homogeneity constraint. The proposed framework is applied in climate science and neuroscience. We show how these methods can be used to evaluate cutting edge climate models and identify lagged relationships between different climate regions. In the context of neuroscience, the method successfully identifies well-known “resting state networks” as well as a few areas forming the backbone of the functional cortical network. Finally, we contrast the proposed methods to dimensionality reduction techniques (e.g., clustering PCA/ICA) and show their limitations.

Dyspnoea (breathlessness) is a debilitating, often poorly controlled, symptom of cardiopulmonary, neurovascular and psychological disorders. This thesis develops the necessary methodology to dissociate aspects of the acute dyspnoea experience using functional magnetic resonance imaging (FMRI) in healthy volunteers. The neuronal mechanisms underlying dyspnoea anticipation, its perceived intensity and unpleasantness and the modulation of these mechanisms by the opioid remifentanil were explored. We investigated the subjective perception of respiratory loading, a commonly used dyspnoea stimulus, and its potential systematic confounds on FMRI due to cerebral blood flow changes. Investigation of the perception of respiratory loading at different levels of hypercapnia (increased end-tidal CO₂) showed that hypercapnia should be kept to a minimum to avoid increased baseline respiratory unpleasantness whilst maintaining the stable arterial CO₂ (isocapnia) beneficial for FMRI analysis. Investigation of the effects of respiratory loading (± 9 cmH₂O) on cerebral blood flow showed that systematic confounds of respiratory loading on perfusion-based neuroimaging data were small (~5%) and did not significantly alter neural activation in response to visual stimulation. Isocapnic respiratory loading during a classical fear-conditioning paradigm during FMRI was used to investigate dyspnoea anticipation, and dissociate the intensity and unpleasantness of acute dyspnoea by modulating unpleasantness with remifentanil. Differential neural networks were found to be involved in perceived intensity (thalamus, insula, somatosensory cortex) and unpleasantness (hippocampus, medial prefrontal cortex). Remifentanil reduced respiratory unpleasantness without affecting the perceived intensity and differentially reduced brain activity during both dyspnoea anticipation and perception. This thesis showed the potential of isocapnic respiratory loading for the study of dyspnoea with FMRI. This stimulus revealed, for the first time, brain activation for dyspnoea anticipation, perceived intensity and unpleasantness. The opioid-sensitive nature of the anticipation and unpleasantness of dyspnoea provides brain targets for future research and might facilitate more effective dyspnoea palliation.

The capacity of animals to navigate through familiar or novel environments depends crucially on the integration of a disparate set of self motion cues. The study begins with one of the most simple, planar visual motion, and investigates the cortical organisation of motion sensitive areas. It finds evidence of columnar organisation in hMT+ and a large scale map in V1. Chapter 3 extends this by using stimuli designed to emulate visual and auditory forward motion. It finds that participants are able to determine their direction with a precision close to that predicted by Bayesian integration. Predictions were made regarding neural processing through a modified divisive normalisation model, which was also used to fit the behavioural adaptation results. The integration of different modalities requires visual and auditory streams to combine at some stage within the sensory processing hierarchy. Previous research suggests the ventral intraparietal region (VIP) may be the seat of such integration. Chapter 4 tests whether VIP does combine these cues and whether the correlation between VIP and the unimodal regions changes depending on the coherence of unimodal stimuli. The presence of such modulation is predicted by some models, such as the divisive normalisation model. The processing of such egocentric self motion cues leads to the updating of allocentric representations, these are believed to be encoded by head direction cells and place cells. The experiment in chapter 5 uses a virtual reality stimulus during fMRI scanning to give participants the sense of moving and navigating. Their location in the virtual environment was decoded above chance from voxels in the hippocampus. No head direction signal was classified above chance from any of the three cortical regions investigated. We tentatively conclude that head direction is considerably more difficult to classify from the BOLD signal, possibly due to the homogeneous organisation of head direction cells.

Emerging evidence suggests that hippocampal memory processing is modulated by midbrain regions under conditions of reward, resulting in enhanced encoding of episodic information—long-term memory for events. Current theories further suggest that hippocampal subregions may have distinct roles in episodic memory formation, and may be differentially influenced by dopaminergic midbrain inputs. Using high-resolution functional magnetic resonance imaging (fMRI), the present study investigated hippocampal subregional function as well as activation in surrounding medial temporal lobe (MTL) cortex, midbrain, and nucleus accumbens during associative encoding and cued recall under varying conditions of reward. A high-value or low-value monetary cue preceded a pair of objects indicating potential reward for successful retrieval of the association. At test, participants performed cued recall followed by match (correct association) or mismatch (incorrect association) probe decisions and received feedback on their performance. Behaviorally, cued recall performance was superior for pairs preceded by high reward cues at encoding relative to pairs preceded by low reward cues. FMRI analysis revealed regions within hippocampus, parahippocampal cortex, nucleus accumbens, and midbrain showing subsequent memory effects (greater encoding activation for remembered, compared to forgotten associations) and reward effects (greater activation for high-value, compared to low-value associations) during stimulus encoding. Within several of these regions, individual differences in reward-related encoding activation were correlated with the degree of the behavioral reward effect (better memory for high-value compared to low-value object pairs). At retrieval, regions in midbrain and subiculum predicted successful associative recall, and regions within hippocampus, parahippocampal cortex, nucleus accumbens, and midbrain showed reward effects in the absence of explicit reward cues. Within several MTL regions, activation was greater for match than mismatch probes. These findings are consistent with theories suggesting that reward-based motivation influences memory formation through interactions between dopaminergic midbrain and hippocampus. / text

Previous research has investigated intentional retrieval of contextual information and contextual influences on object identification and word recognition, yet few studies have systematically investigated context effects in episodic memory for objects. To address this issue, unique objects on a white background or embedded in a visually rich context were presented to participants. At test, the object was presented either in the original or a different context. Chapter 2 demonstrated that a context shift decrement (CSD)--decreased recognition performance when context is changed between encoding and retrieval--was observed. In four studies with young adults, the CSD was not attenuated by encoding or retrieval manipulations. Chapter 3 revealed that the CSD was resistant to aging and neuropsychological status. Importantly, older adults classified as high MTL performed better on the recognition task than those classified as low MTL, and as well as young adults, supporting the successful aging hypothesis. Chapter 4 focused on elucidating the neural correlates of the CSD using functional Magnetic Resonance Imaging. Right PHG activation during encoding was associated with subsequent recognition of objects in the context change condition. This same region was activated during recognition, suggesting it may automatically reinstate visual contextual information. Overall, the CSD is attributed to the automatic and obligatory binding of object and context information in episodic memory that results in an integrated representation, mediated by the hippocampal complex.