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Development and Developmental Disorders
Published in Andrei I. Holodny, Functional Neuroimaging, 2019
The human visual pathway contains both magnocellular and parvocellular components. The magnocellular component of the visual pathway system (M pathway) is geared toward identification of object movement and luminance contrast, whereas the parvocellular system is geared for detailed static and color imagery.
Developmental Dyslexia
Published in Ivanka V. Asenova, Brain Lateralization and Developmental Disorders, 2018
Reading requires fast and accurate processing of transient visual and auditory stimuli and the largest cells in the brain, known as magnocellular neurons, are specialized in this type of processing. Magnocellular neurons are highly myelinated and transmit and process rapidly changing sensory and motor signals along the nervous system. Notably, the magnocellular visual system is responsible for timing events in the visual world and plays a particularly important role in motion perception and the control of eye movements (saccades, tracking, fixation) (for details, see [206, 208]).
Disruptions in physical substrates of vision following traumatic brain injury
Published in Mark J. Ashley, David A. Hovda, Traumatic Brain Injury, 2017
Vision is a major functional system in the brain. Kandel’s book Principles of Neural Science describes the five principles governing the organization of the brain’s functional systems.12 The first is that each functional system involves several brain regions that carry out different types of information processing. An example in the visual system would be the retina, superior colliculus, LGN, pulvinar, and PVC. These are not merely relay stations in that modification of visual information occurs at each step. The second principle is that identifiable pathways link the components of the functional system. In the case of vision, the major pathways include the retinogeniculocortical pathway and the dorsal and ventral streams. The third principle is that each point of the brain projects in an early fashion onto the next via topographic maps. Retinotopic maps are the visual maps that fulfill this criteria. The fourth principle is that functional systems are hierarchically organized. In vision, the hierarchical arrangement for more selective and advanced processing begins in the retina and passes via the retinocortical tract to the dorsal and ventral streams. In addition, there is also parallel processing with the magnocellular and parvocellular systems processing for motion, color, and form, respectively. The last principle states that one side of the brain controls the opposite side of the body, which is important in visual brain representations in that one side of the brain represents the contralateral visual field.
Diagnostic performance of a modified visual perception test
Published in Hearing, Balance and Communication, 2023
Mayada Elsherif, Mona Mourad, Nesrine Hamouda, Rania Abdou, Taima Salem
In our study, dyslexic children showed significantly lower scores from non-dyslexic in the identification of the colour of the optotype presented to them in saccadic and distractor tasks. This may be urged to the interaction between the parvocellular and magnocellular systems. In dyslexic children, Ahmadi et al. [26] revealed a parvocellular system deficit. They did so by presenting colourful sensory images in the form of natural environment photographs and utilizing the psycho-physical technique (subjectively) to determine the red-green isoluminant point. Bonfiglio et al. [27] discovered that dyslexic children displayed delayed visual evoked potential to achromatic stimulus (magnocellular-dorsal stream) along with isoluminant red/green and blue/yellow stimulus (parvocellular-ventral and koniocellular streams). They were able in demonstration such weakness objectively.
Focus on eye care in schizophrenia
Published in Clinical and Experimental Optometry, 2019
Clinically, the predilection toward impaired magnocellular function associated with some patients with schizophrenia may present during frequency doubling perimetry. Frequency doubling technology is commonly used in eye clinics for visual field screening as well as threshold testing. This technology differs from white‐on‐white perimetry in that the target image has features of low spatial and high temporal frequency, creating a doubling effect that aims to selectively stimulate the magnocellular pathway. The magnocellular pathway specifically drives visual perception of low spatial frequency and high temporal frequency stimuli.2013 Frequency doubling technology is thought to highlight visual field loss earlier in glaucoma disease due to reduced redundancy of the magnocellular cell type.
Optical coherence tomography in the investigation of systemic neurologic disease
Published in Clinical and Experimental Optometry, 2019
Sangeetha Srinivasan, Nathan Efron
A decrease in macular volume has been noted in patients with multiple sclerosis,2009 more so in the nasal portions,2010 which may corroborate with compromised retinal nerve fibre layer thickness in the temporal quadrant as reported in a previous study.2017 Evangelou et al.2001 examined the size distribution of neurons in the magnocellular and parvocellular layers of the lateral geniculate body, and axonal densities of the anterior visual pathway. They observed that the distribution of neuron size in the lateral geniculate body was correlated with axonal densities in the visual pathway. In addition, they observed there were no significant differences in neuronal size distribution between patients and controls in magnocellular layers. In parvocellular layers, cell sizes were smaller in those with multiple sclerosis compared with those of healthy controls, suggesting that smaller axons may be susceptible to damage from multiple sclerosis.2001