A physiological basis for visual discomfort: Application in lighting design

Visual discomfort occurs when the statistics of the retinal image depart from those of natural scenes, particularly in respect of an excess energy at spatial frequencies close to 3 cycles/degree. Computer models suggest that uncomfortable stimuli are processed with a larger and less sparse neural response. Uncomfortable stimuli usually evoke a relatively large oxygenation of the visual cortex of the brain, consistent with inefficient neural encoding. The discomfort may be homeostatic. The neural computation that sustains sight is therefore likely to be more complex when the visual scene is spatially periodic, when the colour contrast is high or when saccadic suppression is impaired by flicker that is too rapid to be seen. </jats:p

Nuevas técnicas de imagen en el estudio de la displasia cortical focal infantil: resonancia magnética de 3T con antena multicanal y PET-FDG

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid. Facultad de Medicina, Departamento de Anatomía, Hisotlogía y Neurociencia. Fecha de lectura:12 de Julio de 201

Long-term quality assurance of fMRI and MRS on a 3.0T clinical scanner

Functional MRI (fMRI) and Magnetic Resonance Spectroscopy (MRS) are being increasingly used in clinical protocols. Subsequenly it is crucial to develop a routine quality assurance protocol (QA)of both techniques. This work describes a long-term variability study, as apart of the QA of fMRI and MRS on our institution clinical 3.0 T MR scanner

Changes in the Papez Circuit in early stages of Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of demenMa. Neuronal and synapMc losses occur iniMally and predominantly in the medial temporal lobe structures including hippocampus, amygdala and thalamus, structures that belong to the Papez circuit. The integrity of the connecMons amongst them is essenMal for episodic memory, which is specifically impaired in AD. For this reason we have invesMgated the degeneraMon paRern of subcorMcal structures and its relaMon to early stages of AD, i.e. Mild CogniMve Impairment (MCI), both in the amnesic and mulMdomain types using structural magneMc resonance imaging (using a 3T GE scanner) and VBM‐DARTEL

Diffusion Tensor Imaging in Alzheimer's disease

Attentional control and Information processing speed are central concepts in cognitive psychology and neuropsychology. Functional neuroimaging and neuropsychological assessment have depicted theoretical models considering attention as a complex and non-unitary process. One of its component processes, Attentional set-shifting ability, is commonly assessed using the Trail Making Test (TMT). Performance in the TMT decreases with increasing age in adults, Mild Cognitive Impairment (MCI) and Alzheimer’s Disease (AD). Besides, speed of information processing (SIP) seems to modulate attentional performance. While neural correlates of attentional control have been widely studied, there are few evidences about the neural substrates of SIP in these groups of patients. Different authors have suggested that it could be a property of cerebral white matter, thus, deterioration of the white matter tracts that connect brain regions related to set-shifting may underlie the age-related, MCI and AD decrease in performance. The aim of this study was to study the anatomical dissociation of attentional and speed mechanisms. Diffusion tensor imaging (DTI) provides a unique insight into the cellular integrity of the brain, offering an in vivo view into the microarchitecture of cerebral white matter. At the same time, the study of ageing, characterized by white matter decline, provides the opportunity to study the anatomical substrates speeded or slowed information processing. We hypothesized that FA values would be inversely correlated with time to completion on Parts A and B of the TMT, but not the derived scores B/A and B-A

Refining memory assessment of elderly people with cognitive impairment:Insights from the short-term memory binding test

Alzheimer’s disease (AD) affects temporary memory for bound features more remarkably than for individual features. Such selective impairments manifest from presymptomatic through dementia stages via titration procedures. A recent study suggested that without titration and with high memory load the binding selectivity may disappear in people at risk of AD such as those with Mild Cognitive Impairment (MCI). We compared data from two studies on temporary binding which assessed people with MCI and controls using different memory loads (2 or 3 items). Selective binding impairments were found in MCI, but relative to controls, such selectivity was contingent upon memory load (i.e., present with 2 items). Further analysis with MCI people who tested positive to neuroimaging biomarkers (i.e., hippocampal atrophy) confirmed that this specific binding impairments are a feature of prodromal AD. The temporary binding task has been recently suggested by consensus papers as a potential screening tool for AD. The results presented here inform on task properties that can maximise the reliability of this new assessment tool for the detection of memory impairments in prodromal cases of AD

Discomfort from urban scenes: Metabolic consequences

Scenes from nature share in common certain statistical properties. Images with these properties can be processed efficiently by the human brain. Patterns with unnatural statistical properties are uncomfortable to look at, and are processed inefficiently, according to computational models of the visual cortex. Consistent with such putative computational inefficiency, uncomfortable images have been demonstrated to elicit a large haemodynamic response in the visual cortex, particularly so in individuals who are predisposed to discomfort. In a succession of five small-scale studies, we show that these considerations may be important in the design of the modern urban environment. In two studies we show that images from the urban environment are uncomfortable to the extent that their statistical properties depart from those of scenes from nature. In a third study we measure the haemodynamic response to images of buildings computed as having unnatural or natural statistical properties, and show that in posterior brain regions the images with unnatural statistical properties (often judged uncomfortable) elicit a haemodynamic response that is larger than for images with more natural properties. In two further studies we show that judgments of discomfort from real scenes (both shrubbery and buildings) are similar to those from images of the scenes. We conclude that the unnatural scenes in the modern urban environment are sometimes uncomfortable and place excessive demands on the neural computation involved in vision, with consequences for brain metabolism, and possibly also for health

Changes in resting-state functionally connected parieto-frontal networks after videogame practice

Neuroimaging studies provide evidence for organized intrinsic activity under task-free conditions. This activity serves functionally relevant brain systems supporting cognition. Here, we analyze changes in resting-state functional connectivity after videogame practice applying a test–retest design. Twenty young females were selected from a group of 100 participants tested on four standardized cognitive ability tests. The practice and control groups were carefully matched on their ability scores. The practice group played during two sessions per week across 4 weeks (16 h total) under strict supervision in the laboratory, showing systematic performance improvements in the game. A group independent component analysis (GICA) applying multisession temporal concatenation on test–retest resting-state fMRI, jointly with a dual-regression approach, was computed. Supporting the main hypothesis, the key finding reveals an increased correlated activity during rest in certain predefined resting state networks (albeit using uncorrected statistics) attributable to practice with the cognitively demanding tasks of the videogame. Observed changes were mainly concentrated on parietofrontal networks involved in heterogeneous cognitive functions

Structural changes after videogame practice related to a brain network associated with intelligence

Here gray and white matter changes after four weeks of videogame practice were analyzed using optimized voxel-based morphometry (VBM), cortical surface and cortical thickness indices, and white matter integrity computed from several projection, commissural, and association tracts relevant to cognition. Beginning with a sample of one hundred young females, twenty right handed participants were recruited for the study and assigned to a practice or a control group carefully matched by their general cognitive ability scores. After the first scan, the practice group played ‘Professor Layton and The Pandora's Box’ 4 h per week during four weeks. A second scan was obtained at the end of practice and intelligence was measured again. Image analyses revealed gray and white matter changes in the practice group. Gray matter changes theoretically relevant for intelligence were observed for the practice group mainly in frontal clusters (Brodmann areas 9 and 10) and also in smaller parietal and temporal regions. White matter findings were focused in the hippocampal cingulum and the inferior longitudinal fasciculus. These gray and white matter changes presumably induced by practice did not interact with intelligence tests' scores