Multiple sclerosis reduces synchrony of the magnocellular pathway

Multiple Sclerosis (MS) is an autoimmune demyelinating disease that damages the insulation of nerve cell fibers in the brain and spinal cord. In the visual system, this demyelination results in a robust delay of visually evoked potentials (VEPs), even in the absence of overt clinical symptoms such as blurred vision. VEPs, therefore, offer an avenue for early diagnosis, monitoring disease progression, and, potentially, insight into the differential impairment of specific pathways. A primary hypothesis has been that visual stimuli driving the magno-, parvo-, and konio-cellular pathways should lead to differential effects because these pathways differ considerably in terms of myelination. Experimental tests of this hypothesis, however, have led to conflicting results. Some groups reported larger latency effects for chromatic stimuli, while others found equivalent effects across stimulus types. We reasoned that this lack of pathway specificity could, at least in part, be attributed to the relatively coarse measure of pathway impairment afforded by the latency of a VEP. We hypothesized that network synchrony could offer a more sensitive test of pathway impairments. To test this hypothesis, we analyzed the synchrony of occipital electroencephalography (EEG) signals during the presentation of visual stimuli designed to bias activity to one of the three pathways. Specifically, we quantified synchrony in the occipital EEG using two graph-theoretic measures of functional connectivity: the characteristic path length (L; a measure of long-range connectivity) and the clustering coefficient (CC; a measure of short-range connectivity). Our main finding was that L and CC were both smaller in the MS group than in controls. Notably, this change in functional connectivity was limited to the magnocellular pathway. The effect sizes (Hedge’s g) were 0.89 (L) and 1.26 (CC) measured with magno stimuli. Together, L and CC define the small-world nature of a network, and our finding can be summarized as a reduction in the small-worldness of the magnocellular network. We speculate that the reduced efficiency of information transfer associated with a reduction in small-worldness could underlie visual deficits in MS. Relating these measures to differential diagnoses and disease progression is an important avenue for future work.

Visual Magnocellular Deficits In Dyslexia : Are These Deficits Due To Co-morbidity With ADHD?

Some cases of dyslexia may be accounted for by a visual problem involving the magnocellular pathways. Research on dyslexia and problems in the magnocellular pathway has been controversial. Some studies indicate that individuals with dyslexia have problems in this pathway whereas other studies have not. It may be that only the individuals with both dyslexia and ADHD have problems in this pathway while individuals with dyslexia only are spared. In support of this, research has shown that individuals with schizophrenia have attention deficits (similar to those seen in individuals with ADHD) and problems in the magnocellular pathway. In the present study, controls, participants with dyslexia only, participants with both dyslexia and ADHD, and participants with ADHD only completed central and peripheral backward masking experiments. It was predicted that the two groups of participants with ADHD would have problems in the magnocellular pathway. Some evidence was found in support of this.

Visual Magnocellular Deficits In Dyslexia : Are These Deficits Due To Co-morbidity With ADHD?

Some cases of dyslexia may be accounted for by a visual problem involving the magnocellular pathways. Research on dyslexia and problems in the magnocellular pathway has been controversial. Some studies indicate that individuals with dyslexia have problems in this pathway whereas other studies have not. It may be that only the individuals with both dyslexia and ADHD have problems in this pathway while individuals with dyslexia only are spared. In support of this, research has shown that individuals with schizophrenia have attention deficits (similar to those seen in individuals with ADHD) and problems in the magnocellular pathway. In the present study, controls, participants with dyslexia only, participants with both dyslexia and ADHD, and participants with ADHD only completed central and peripheral backward masking experiments. It was predicted that the two groups of participants with ADHD would have problems in the magnocellular pathway. Some evidence was found in support of this.

The Serpentine Illusion: A Visual Motion Illusion Induced by Phase-Shifted Line Gratings

In a pattern of horizontal lines containing ± 45° zigzagging phase-shifted strips, vivid illusory motion is perceived when the pattern is translated up or down at a moderate speed. Two forms of illusory motion are seen: [i] a motion “racing” along the diagonal interface between the strips and [ii] lateral (sideways) motion of the strip sections. We found the relative salience of these two illusory motions to be strongly influenced by the vertical spacing and length of the line gratings, and the period length of the zigzag strips. Both illusory motions are abolished when the abutting strips are interleaved, separated by a gap or when a real line is superimposed at the interface. Illusory motion is also severely weakened when equiluminant colored grating lines are used. Illusory motion perception is fully restored at < 20% luminance contrast. Using adaptation, we find that line-ends alone are insufficient for illusory motion perception, and that both physical carrier motion and line orientation are required. We finally test a classical spatiotemporal energy model of V1 cells that exhibit direction tuning changes that are consistent with the direction of illusory motion. Taking this data together, we constructed a new visual illusion and surmise its origin to interactions of spatial and temporal energy of the lines and line-ends preferentially driving the magnocellular pathway.

Binocular treatment in adult amblyopia is based on parvocellular or magnocellular pathway

Introduction: Amblyopia is speculated to be an untreatable disease in the patient, who is beyond the critical period of vision; however, currently, it is treatable in adults. Purpose: This study aimed to elucidate whether the treatment is useful in both anisometropic amblyopia and strabismic amblyopia. In addition, the differences were detected between anisometropic amblyopia and strabismic amblyopia after the same perceptual treatment and whether the suppression in anisometropic amblyopia or strabismic amblyopia could be decreased before and after the treatment. Methods: A binocular perceptual learning was applied for the treatment, the suppression was measured, and the patients were followed up for 2 months after training. Anisometropic amblyopia and strabismic amblyopia groups were subjected to the assessment of stereo, visual acuity, contrast sensitivity, and suppression before and after the training. Results: After 6 weeks of “Diploma Gabor Orientation Coherence” training, in the anisometropic amblyopia group, the outcomes of visual acuity (t = 3.114, p = 0.026) and contrast sensitivity (t = 7.786, p = 0.001) were increased significantly. While in the strabismic amblyopia group, the outcomes of stereo (t = 2.987, p = 0.040) and contrast sensitivity (t = 3.638, p = 0.022) were increased significantly. Conclusion: After Diploma Gabor Orientation Coherence training in the same frequency and in the same duration, the anisometropic amblyopia group got an improvement in visual acuity, but the strabismic amblyopia group got an improvement in stereo. As there are evidences to show that anisometropic amblyopia and strabismic amblyopia were injured in different pathways, we think the diverse results might come from the different pathway injury in anisometropic amblyopia and strabismic amblyopia.