Abstract
Macular degeneration (MD) causes central vision loss, removing input to corresponding representations in the primary visual cortex. There is disagreement concerning whether the cortical regions deprived of input can remain responsive, and the source of reported cortical responses is still debated. To simulate MD in controls, normally sighted participants viewed a bright central disk to adapt the retina, creating a transient ‘retinal lesion’ during a functional MRI experiment. Participants viewed blocks of faces, scrambled faces and uniform grey stimuli, either passively or whilst performing a one-back task. To assess the impact of the simulated lesion, participants repeated the paradigm using a more conventional mean luminance simulated scotoma without adaptation. Our results suggest our attempt to create a more realistic simulation of a lesion did not impact on responses in the representation of the simulated lesion. While most participants showed no evidence of stimulus-driven activation within the lesion representation, a few individuals (22%) exhibited responses similar to a participant with juvenile MD who completed the same paradigm (without adaptation). Reliability analysis showed that responses in the representation of the lesion were generally consistent irrespective of whether positive or negative. We provide some evidence that peripheral visual stimulation can also produce responses in central representations in controls while performing a task. This suggests that the ‘signature of reorganization of visual processing’, is not found solely in patients with retinal lesions, consistent with the idea that activity may be driven by unmasked top–down feedback.
Highlights
Macular degeneration (MD) is a progressive eye disease which causes the loss of vision in the central part of the visual field
JMD exhibited an increase in lesion projection zone’ (LPZ) responses when viewing faces (Fig. 2A)
The positive BOLD responses are not limited to the region of interest (ROI) in which we analyse the data below, but we note that the LPZ represents a visual field area considerably smaller than JMD’s visual field defect
Summary
Macular degeneration (MD) is a progressive eye disease which causes the loss of vision in the central part of the visual field. Following degeneration of the retina, the corresponding representations in primary visual cortex (V1) are deprived of input This has led to a number of studies exploring whether the region deprived of cortical input, known as the ‘lesion projection zone’ (LPZ), might reorganise and take on a new role, processing inputs from intact retina (Baker et al 2005, 2008; Baseler et al 2011; Dilks et al 2009; Hoffmann et al 2003; Sunness et al 2004). Reorganization can refer to structural changes occurring in the brain following acquired or congenital eye disease, but more frequently, it refers to functional changes, whereby patterns of neural activation differ from those observed in healthy individuals. Reorganization refers to patterns of activity within the LPZ that cannot be explained by (a) known properties of the visual system and (b) the absence of visual input (Engel et al 2015; Morland 2015)
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