Khazar Ahmadi

Khazar Ahmadi
Ruhr-Universität Bochum | RUB · Neuropsychology

PhD

About

25
Publications
1,954
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137
Citations
Education
August 2014 - October 2019

Publications

Publications (25)
Article
Full-text available
Autosomal recessive Achromatopsia (ACHM) is a rare inherited disorder associated with dysfunctional cone photoreceptors resulting in a congenital absence of cone input to visual cortex. This might lead to distinct changes in cortical architecture with a negative impact on the success of gene augmentation therapies. To investigate the status of the...
Article
A large body of evidence has shown decreased cerebral blood flow (CBF) in Alzheimer’s disease (AD). However, the link between CBF and the primary AD pathologies as well as synaptic integrity remains unclear. Baseline CBF was measured using arterial spin labeling (ASL) in a 3T MRI scanner in 137 cognitively unimpaired individuals with and without am...
Article
Full-text available
We describe a collection of T1-, diffusion- and functional T2*-weighted magnetic resonance imaging data from human individuals with albinism and achiasma. This repository can be used as a test-bed to develop and validate tractography methods like diffusion-signal modeling and fiber tracking as well as to investigate the properties of the human visu...
Article
Full-text available
Most individuals with congenital achromatopsia (ACHM) carry mutations that affect the retinal phototransduction pathway of cone photoreceptors, fundamental to both high acuity vision and colour perception. As the central fovea is occupied solely by cones, achromats have an absence of retinal input to the visual cortex and a small central area of bl...
Preprint
Full-text available
Autosomal recessive Achromatopsia (ACHM) is a rare inherited disorder associated with dysfunctional cone photoreceptors resulting in a congenital absence of cone input to visual cortex. This might lead to distinct changes in cortical architecture with a negative impact on the success of gene augmentation therapies. To investigate the status of the...
Preprint
Full-text available
Although several studies have shown decreased cerebral blood flow (CBF) in Alzheimer's disease (AD), the role of hypoperfusion in the disease pathogenesis remains unclear. Combining arterial spin labeling MRI, positron emission tomography, and biomarkers of cerebrospinal fluid, we investigated the associations between CBF and the key mechanisms in...
Article
Full-text available
In humans, each hemisphere comprises an overlay of two visuotopic maps of the contralateral visual field, one from each eye. Is the capacity of the visual cortex limited to these two maps or are plastic mechanisms available to host more maps? We determined the cortical organization of the visual field maps in a rare individual with chiasma hypoplas...
Article
Full-text available
The characterization of receptive field (RF) properties is fundamental to understanding the neural basis of sensory and cognitive behaviour. The combination of non-invasive imaging, such as fMRI, with biologically inspired neural modelling has enabled the estimation of population RFs directly in humans. However, current approaches require making nu...
Article
Full-text available
Objective: The human optic chiasm comprises partially crossing optic nerve fibers. Here we used diffusion MRI (dMRI) for the in-vivo identification of the abnormally high proportion of crossing fibers found in the optic chiasm of people with albinism. Methods: In 9 individuals with albinism and 8 controls high-resolution 3T dMRI data was acquire...
Article
In albinism, the pathological decussation of the temporal retinal afferents at the optic chiasm leads to superimposed representations of opposing hemifields in the visual cortex. Here, we assessed the equivalence of the two representations and the cortico-cortical connectivity of the early visual areas. Applying fMRI-based population receptive fiel...
Preprint
Full-text available
The characterization of receptive field (RF) properties is fundamental to understanding the neural basis of sensory and cognitive behaviour. The combination of non-invasive imaging, such as fMRI, with biologically inspired neural modeling has enabled the estimation of population RFs directly in humans. However, current approaches require making num...
Preprint
Full-text available
In humans, each hemisphere comprises an overlay of two visuotopic maps of the contralateral visual field, one from each eye. Is the capacity of the visual cortex limited to these two maps or are plastic mechanisms available to host more maps? Using an integrative approach of submillimeter fMRI, diffusion-weighted imaging and population receptive fi...
Preprint
Full-text available
Objective: The human optic chiasm comprises partially crossing optic nerves. Here we used diffusion MRI (dMRI) for the in-vivo identification of optic chiasm abnormalities in albinism, i.e. enhanced optic nerves crossing. Methods: In 9 individuals with albinism and 8 controls high-resolution 3T dMRI data were acquired and analysed with a set of met...
Preprint
Full-text available
In albinism, the pathological decussation of the temporal retinal afferents at the optic chiasm leads to superimposed representations of opposing hemifields in the visual cortex. Here, we assessed the equivalence of the two representations and the cortico-cortical connectivity of the early visual areas. Applying fMRI-based population receptive fiel...
Article
Due to an increased crossing of the optic nerve fibers at the optic chiasm in albinism, the visual cortex receives largely monocular input from the contralateral eye. Here we investigated whether this obstruction of binocular integration at the cortical input stage also impacts on interocular information exchange at the high processing level of vis...
Article
A fundamental scheme in the organization of the early visual cortex is the retinotopic representation of the contralateral visual hemifield on each hemisphere. We determined the cortical organization in a novel congenital visual pathway disorder, FHONDA-syndrome, where the axons from the temporal retina abnormally cross to the contralateral hemisph...
Article
Current developments in functional magnetic resonance imaging (fMRI) of the human visual system have generated a set of powerful approaches that are of great promise for modern ophthalmology. These make it possible to perform an objective spatially resolved test of visual function in patients with strong visual impairment and even to investigate th...
Conference Paper
Purpose: In congential visual pathway disorders, such as albinism and achiasma, the visual cortex receives input from both visual hemifields, due to a misrouting of the retino-cortical connections at the optic chiasm. In these cases the visual cortex is organised as a retinotopic overlay of both ipsilateral and contralateral visual hemifields with...
Article
Full-text available
Purpose: Dyslexia is one of the most common learning disabilities affecting millions of people worldwide. Although exact causes of dyslexia are not well-known, a deficit in the magnocellular pathway may play a role. We examined possible deficiency of magnocellular, as compared to parvocellular and koniocellular pathway function by measuring lumina...
Article
Postoperative cognitive dysfunction (POCD) is a well-recognized complication of cardiac and noncardiac surgery. However, contradictory results concerning postoperative mental function have been reported. The aim is to determine the effect of anesthetic techniques (general or spinal) on cognitive functions using more sensitive neuropsychological tes...

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Projects

Projects (2)
Project
The goal of this project is to create and publish the repository of high-quality diffusion MRI data. The provided data set is expected to benefit basic neuroscientific research (neuroanatomy in case of abnormal visual system) and methods development (dMRI data preprocessing and tractography).
Project
NextGenVis is a European team of early career research fellows collaborating within a Marie Curie Sklodowska Innovative Training Network. The fellows are drawn from health care sectors, universities and private companies and are all trained within the field of visual and computational neuroscience. The NextGenVis network brings together unique expertise and resources in brain imaging, psychology, neurology, ophthalmology, and computer science. The project is called NextGenVis for a reason: the goal is to take vision research further by Training the Next Generation of Visual Neuroscientists. Training includes both academic research and collaboration with the health care and high-tech industry. The network of fellows are trained in quantitative knowledge on the adaptive properties of the visual brain in health and disease – with a strong focus on the neurocomputational basis – and how to apply this new knowledge to boost innovation in health care and technology.