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New coding mechanism fortransferring information from perception to memory

researchers at Dartmouth College has identified a new neural coding mechanism that enables the transfer of information between perceptual regions and memory areas of the brain

Dartmouth-college , Adam-steel , Eural-coding-mechanism , Erception , Emory , Rain-organization , Etinotopic-mapping , Ush-pull-coding-mechanism ,

"Vascular artefacts in fMRI of early visual cortex: The effects of reso" by Wei Shi Eleanor Koo

Large draining veins residing on the cortical surface are recognised as a major problem in fMRI measurements, leading to the displacement, distortion, and reduction in spatial localisation of signals. This is detrimental to the application of fMRI in advanced human brain imaging, such as in retinotopic mapping, where the BOLD signal becomes obscured by the artefacts from nearby draining veins (venous artefacts). There is consensus that at an increased magnetic field strength, the sensitivity to the contributions from these draining veins reduces, which promises the ability to capture measurements at greater sensitivity and specificity. With the advent of fMRI hardware and technologies, there is a great interest in understanding cortical layer-specific neuronal response that had been previously obscured due to the domination of signal change caused by venous artefacts. This forms the basis of support for fMRI at ultra-high magnetic field strength, with the conventional wisdom that the reduced sensitivity to macrovasculature (including draining veins) that comes with higher magnetic field strength can increase the sensitivity to underlying responses that closely reflect neuronal activation. However, this is debatable. Instead, there are instances where human neuronal response profiles displayed a pattern that seemed indicative of synaptic activities even without using ultra-high magnetic field strength. Recent trends in moving to ultra-high magnetic field strengths, especially for depth-dependent fMRI, beget the questions – is ultra-high magnetic field strength really necessary, and can it resolve the artefacts from draining veins? To elucidate these questions, this thesis aims to test the venous artefact and its impact on underlying signals across spatial resolutions and magnetic field strengths, focusing on the quality of the retinotopic organisation of the early visual cortex. The first experimental study was conducted to test the venous artefact and its impact on fMRI signals across the grey matter using high-resolution (isotropic resolution of 1 mm) fMRI images collected at 3 T. Using two surface reconstruction packages, the findings established that venous artefact occurs at the cortical surface and spreads within the grey matter. In this study, the ability of high-resolution fMRI at 3 T to conduct depth-dependent analyses was demonstrated. The second experimental study delves into the role of spatial resolution in the depth-dependent analysis of venous artefacts and their impact. The 1 mm 3 T fMRI images were spatially smoothed to simulate two additional sets of lower-effective resolution images. Here, the results found consistency in the venous artefact but a reduction in

Vascular-artefacts , Enous-effects , Raining-veins , Etinotopic-mapping ,

"Anomalous responses: Disturbing the order in V4 and human visual cort" by Harriet G. Boyd Taylor

The anatomical location and retinotopic organisation of human V4 has been debated almost from the outset of fMRI. Initially, a large amount of the debate centred around whether V4 organisation in humans mimicked the organisation seen in macaque monkeys and other non-human primates. In these animals, V4 is split into dorsal and ventral components, representing the lower and upper visual quarterfields respectively. In humans however, it appeared from early on that V4 was instead organised into a continuous hemifield retinotopic map on the ventral surface, adjacent to ventral V3. The biggest argument in favour of this was the simple fact that locating a dorsal component to V4 in humans has never been done. In many hemispheres, an obvious hemifield map of V4 is identifiable, but often this is not the case. Instead, V4 sometimes appears to map only half to three quarters of the contralateral hemifield, with the last quarter – including the lower vertical meridian – not being present. With the majority of the visual neuroscience community accepting that V4 is indeed located solely on the ventral surface, the question became why can we not identify a complete map in up to half of hemispheres? The line of inquiry has focussed on the possibility that artefact from nearby draining veins disrupt the signal along the lower boundary, obscuring this region of the map. There is some support that this is the case in at least some hemispheres. The current work aims to resolve incomplete V4 maps in humans. In Chapter 2, we examine the possibility that obscured regions can be revealed by correcting time courses of voxels contaminated with venous artefact. Chapter 3 considers the effect of the phase encoding direction of the MRI scanner itself as a potential cause for incomplete V4 maps, and Chapter 4 examines V4 maps and venous artefact across cortical depth. We show that in some instances V4 maps are recoverable using correction procedures, that the phase encoding direction can alter the appearance of retinotopic maps of V4 and early visual cortex, and how retinotopic maps and venous artefact change across cortical depth.

Human-v4 , Etinotopic-mapping , Mri , Eins , Epth-dependent-fmri , திரு ,