PURPOSE: Activity in regions of the visual cortex corresponding to central scotomas in subjects with macular degeneration (MD) is considered evidence for functional reorganization in the brain. Three unresolved issues related to cortical activity in subjects with MD were addressed: Is the cortical response to stimuli presented to the preferred retinal locus (PRL) different from other retinal loci at the same eccentricity? What effect does the role of age of onset and etiology of MD have on cortical responses? How do functional responses in an MD subject's visual cortex vary for task and stimulus conditions? METHODS: Eight MD subjects-four with age-related onset (AMD) and four with juvenile onset (JMD)-and two age-matched normal vision controls, participated in three testing conditions while undergoing functional magnetic resonance imaging (fMRI). First, subjects viewed a small stimulus presented at the PRL compared with a non-PRL control location to investigate the role of the PRL. Second, they viewed a full-field flickering checkerboard compared with a small stimulus in the original fovea to investigate brain activation with passive viewing. Third, they performed a one-back task with scene images to investigate brain activation with active viewing. RESULTS: A small stimulus at the PRL generated more extensive cortical activation than at a non-PRL location, but neither yielded activation in the foveal cortical projection. Both passive and active viewing of full-field stimuli left a silent zone at the posterior pole of the occipital cortex, implying a lack of complete cortical reorganization. The silent zone was smaller in the task requiring active viewing compared with the task requiring passive viewing, especially in JMD subjects. CONCLUSIONS: The PRL for MD subjects has more extensive cortical representation than a retinal region with matched eccentricity. There is evidence for incomplete functional reorganization of early visual cortex in both JMD and AMD. Functional reorganization is more prominent in JMD. Feedback signals, possibly associated with attention, play an important role in the reorganization.
PURPOSE: Activity in regions of the visual cortex corresponding to central scotomas in subjects with macular degeneration (MD) is considered evidence for functional reorganization in the brain. Three unresolved issues related to cortical activity in subjects with MD were addressed: Is the cortical response to stimuli presented to the preferred retinal locus (PRL) different from other retinal loci at the same eccentricity? What effect does the role of age of onset and etiology of MD have on cortical responses? How do functional responses in an MD subject's visual cortex vary for task and stimulus conditions? METHODS: Eight MD subjects-four with age-related onset (AMD) and four with juvenile onset (JMD)-and two age-matched normal vision controls, participated in three testing conditions while undergoing functional magnetic resonance imaging (fMRI). First, subjects viewed a small stimulus presented at the PRL compared with a non-PRL control location to investigate the role of the PRL. Second, they viewed a full-field flickering checkerboard compared with a small stimulus in the original fovea to investigate brain activation with passive viewing. Third, they performed a one-back task with scene images to investigate brain activation with active viewing. RESULTS: A small stimulus at the PRL generated more extensive cortical activation than at a non-PRL location, but neither yielded activation in the foveal cortical projection. Both passive and active viewing of full-field stimuli left a silent zone at the posterior pole of the occipital cortex, implying a lack of complete cortical reorganization. The silent zone was smaller in the task requiring active viewing compared with the task requiring passive viewing, especially in JMD subjects. CONCLUSIONS: The PRL for MD subjects has more extensive cortical representation than a retinal region with matched eccentricity. There is evidence for incomplete functional reorganization of early visual cortex in both JMD and AMD. Functional reorganization is more prominent in JMD. Feedback signals, possibly associated with attention, play an important role in the reorganization.
Authors: Eric H Schumacher; Julie A Jacko; Susan A Primo; Keith L Main; Kevin P Moloney; Erin N Kinzel; Jimmy Ginn Journal: Restor Neurol Neurosci Date: 2008 Impact factor: 2.406
Authors: David S Friedman; Benita J O'Colmain; Beatriz Muñoz; Sandra C Tomany; Cathy McCarty; Paulus T V M de Jong; Barbara Nemesure; Paul Mitchell; John Kempen Journal: Arch Ophthalmol Date: 2004-04
Authors: Oliver P Hinds; Niranjini Rajendran; Jonathan R Polimeni; Jean C Augustinack; Graham Wiggins; Lawrence L Wald; H Diana Rosas; Andreas Potthast; Eric L Schwartz; Bruce Fischl Journal: Neuroimage Date: 2007-11-06 Impact factor: 6.556
Authors: Mark A Williams; Chris I Baker; Hans P Op de Beeck; Won Mok Shim; Sabin Dang; Christina Triantafyllou; Nancy Kanwisher Journal: Nat Neurosci Date: 2008-11-02 Impact factor: 24.884
Authors: Tina Plank; Jozef Frolo; Fatima Farzana; Sabine Brandl-Rühle; Agnes B Renner; Mark W Greenlee Journal: Hum Brain Mapp Date: 2012-04-16 Impact factor: 5.038
Authors: Heather E Whitson; Ying-Hui Chou; Guy G Potter; Michele T Diaz; Nan-Kuei Chen; Eleonora M Lad; Micah A Johnson; Scott W Cousins; Jie Zhuang; David J Madden Journal: Brain Connect Date: 2014-12-02
Authors: Heidi A Baseler; André Gouws; Koen V Haak; Christopher Racey; Michael D Crossland; Adnan Tufail; Gary S Rubin; Frans W Cornelissen; Antony B Morland Journal: Nat Neurosci Date: 2011-03-27 Impact factor: 24.884