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JJ Sloper, AR Davis, MM Neveu, M Brammer, SC R Williams, FW Fitzke, MJ Morgan, GE Holder, CR Hogg; Different Functional MRI Responses of the Visual Cortex to Magnocellular and Parvocellular Biased Visual Stimuli . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4747.
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Purpose: To compare the BOLD (Blood Oxygen Level Dependant) responses to magnocellular (M) and parvocellular (P) biased stimuli in normal subjects using functional magnetic resonance imaging (fMRI). Methods: Seven normal subjects underwent fMRI scanning. The M-biased stimulus was a 60' black and white chequerboard reversing at 10 Hz (50% duty cycle). The P-biased stimulus was a 10' black and white chequerboard, reversing at 2 Hz (50% duty cycle). The fMRI paradigm was an on/off design with a 21 second on and 21 second off period. The viewing distance was 2 metres with a visual field of 13 degrees. Stimuli were presented at 5, 10, 20, 40 and 80% contrast and were viewed monocularly using a mirror mounted on the head coil of the magnet. Scans were performed in a 1.5 Tesla scanner and analysed using in-house software (1). Analysis of variance was performed using the F-test. Results: The M-biased stimulus produced significant activation of V1at all contrast levels, with the exception of 10% contrast in the right hemisphere. These responses saturated at 20% contrast. The M-biased stimulus also produced significant activation in the visual motion area (V5) at all contrast levels in both hemispheres, with a maximum response at 80% contrast in the right hemisphere The P-biased stimulus produced significant activation in V1 only at 80% contrast (F 2,208 = 4; p<0.01). Conclusion: M and P-biased stimuli evoked different patterns of BOLD response in visual cortical areas of normal subjects. These stimuli should allow exploration of clinical conditions such as amblyopia, which may have differing M and P system involvement. Reference: 1. Bullmore E, Brammer M, Williams SC, et al. Statistical methods of estimation and inference for functional MR image analysis. Magnetic Resonance in Medicine 1996;35:261-77.
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