Functional MRI Response To The Filling–In Process

Abstract

Abstract: : Purpose: We have investigated whether filling–in of an artificial central scotoma influences activity in the primary visual cortex, using the method of functional magnetic resonance imaging (fMRI). Methods: Blood oxygenation level–dependant fMRI was performed at 1.5 Tesla on nine healthy volunteers. Visual stimuli were presented to the subjects using a rear projection and mirror system whilst recording eye movements. The first stimuli comprised a rotating windmill pattern, presented with and without a central black spot 7.5° in diameter. The second stimuli consisted of an incoherent ‘broken’ windmill pattern, presented with and without the same central scotoma. A third stimulus consisted of a small rotating windmill, also covering 7.5° of the central visual field. Results: All subjects reported filling–in, or merging of the peripheral pattern into the centre of the rotating windmill stimulus, when it was presented with a central blank spot. No subjects reported filling–in when viewing the broken windmill stimulus with the same central blank spot. The subjects maintained fixation during the tests. Comparing the difference in brain activation maps between viewing the broken windmill pattern with and without central blank spot demonstrated a cortical region of activation consistent with the presentation of a central stimulus. The difference was significantly less marked when the rotating windmill, or filling–in stimulus, was compared with and without a central blank spot. Conclusions: Brain activation maps measured in nine volunteers using fMRI, have demonstrated that central filling–in is accompanied by increased neuronal activity in the primary visual cortex. This suggests that an active cortical process is taking place.

Keywords: perception • visual cortex • neuro–ophthalmology: cortical function/rehabilitation