fMRI with Central Vision Loss: Effects of Fixation Locus and Stimulus Type

Abstract

The observed results suggest that naturalistic images are more likely to trigger top-down processes that regulate activation in early visual cortex in patients with central vision loss.

Cerebral Modifications and Visual Pathway Reorganization in Maculopathy: A Systematic Review

“…-Oculomotor training, mainly aimed at the use of a PRL to obtain stability in eccentric fixation, has a positive effect on the performances obtained in the visual task (Plank et al, 2014). These effects are accompanied both by structural changes in the cerebellum (Rosengarth et al, 2013) and by interesting functional changes, where PRL stimulation generates a response of the LPZ, and greater fixation stability corresponds to a greater consequent activation (Plank et al, 2017). -In multiple occasions, PRL stimulation was investigated: in patients using PRL for visual elaboration, its stimulation has proven to trigger a more extensive visual cortical activation than in patients not using it (Plank et al, 2013); in particular, stimulation of the PRL was able in some studies to activate that very cortical area normally receiving input from the lesioned macula (Baker et al, 2008;Masuda et al, 2008;Schumacher et al, 2008;Plank et al, 2017) but not in all of them (Liu et al, 2010).…”

“…It should be noted that there is one study that did not detect the activation of LPZ by the PRL by using only passive visual stimuli, without visual task. -The nature of the stimulus seems also to influence brain response (Plank et al, 2017): object pictures were found to elicit stronger responses of the central representation area in the visual cortex than did the flickering checkerboard, probably due to feedback projections from higher visual areas. -Finally, against the hypothesis of remodeling, it was pointed out by Haak et al (2016) that a retinotopic organization of the visual cortex has proven to persist although long after the deafferentation generated by AMD, even if decreased in comparison to healthy controls.…”

“…Patient characteristics are reported in Table 1. The following techniques were used for investigating brain changes: Hernowo et al (2014), Haak et al (2016), and Prins et al (2016) share the same patients, Plank et al (2011Plank et al ( , 2013Plank et al ( , 2017 shared some of the patients median value of age. Y, young; O, old; NS, not specified; NA, not applicable; PRL, preferred retinal locus; VF, visual field; AMD, age-related macular dystrophy.…”

“…This enhancement was also accompanied by an increased response in the PRL projection zone of the visual cortex. Plank et al (2017) used fMRI on JMD patients and controls to examine whether a visual stimulation of PRL would have caused a greater activation of the visual cortex in comparison with stimulating an equivalent peripheral area in the opposite hemifield (oppPRL). Retinal loci were stimulated using a flickering checkerboard and real-object pictures during fMRI measurement.…”

“…An eligible candidate to fight this effect seems to come from digestion of their glycosaminoglycan chains, thanks to the enzyme chondroitinase ABC (ChABC): interestingly, administration of ChABC after spinal cord injury permits some axon regeneration and greatly increases plasticity, and when combined with appropriate rehabilitation, ChABC treatment can lead to a considerable restoration of function, even in patients with neurodegenerative diseases (Fawcett, 2015). Since rehabilitation attempts through exercises and oculomotor training (Rosengarth et al, 2013;Plank et al, 2014Plank et al, , 2017 can be a worthwhile option but can achieve results only if these structural and functional modifications in the visual system occur, we can imagine, as a possible future therapeutic perspective, a combination of specific oculomotor and visual training and pharmacological stimulation of neuroplasticity aimed at obtaining a percentage of improvement in both AMD and JMD patients (Kwok et al, 2008;Fawcett, 2009;Yang et al, 2015;de Winter et al, 2016;Restani and Caleo, 2016;Foscarin et al, 2017).…”