The effect of age and fixation instability on retinotopic mapping of primary visual cortex
Michael D. Crossland 1*,
Antony B Morland 2,
Mary P Feely 3,
Elisabeth A. H. von dem Hagen 4,
and
Gary S. Rubin 3
1 Institute of Ophthalmology, University College London, Vision Rehabilitation, London, EC1V 9EL, United Kingdom
2 York University, York, United Kingdom
3 Institute of Ophthalmology, University College London, London, United Kingdom
4 MRC Cognition & Brain Sciences Unit, Cambridge, United Kingdom
* To whom correspondence should be addressed. E-mail: m.crossland{at}ucl.ac.uk.
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Abstract |
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Purpose: Functional magnetic resonance imaging (fMRI) experiments determining the retinotopic structure of visual cortex have commonly been performed on young adults who are assumed to be able to maintain steady fixation throughout the trial duration. Here we quantify the effects of age and fixation stability on the quality of retinotopic maps of primary visual cortex.
Methods: Using a 3T fMRI scanner, we measured cortical activity in 6 older and 6 younger normally-sighted participants observing an expanding flickering checkerboard stimulus of diameter 30°. The area of flattened primary visual cortex (V1) showing any blood oxygen level dependent (BOLD) activity to the visual stimulus, and the area responding to the central 3.75° of the stimulus (relating to the central ring of our target) were recorded. Fixation stability was measured while participants observed the same stimuli outside the scanner using an infrared gazetracker.
Results: There were no changes in the area of V1 with age. However, the proportion of V1 active to our visual stimulus was lower for the older than the younger observers (overall activity: 89.8% of V1 area for older observers; 98.6% for younger observers, p<0.05). This effect was more pronounced for the central 3.75° of the target (older subjects: 26.4%; younger subjects: 40.7%; p<0.02). No significant relationship existed between fixation stability and age or the magnitude of activity in primary visual cortex.
Conclusions: Although cortical area remains unchanged, healthy older people show less BOLD activity in V1 than younger people. Normal variations in fixation stability do not have a significant effect on the accuracy of experiments to determine the retinotopic structure of visual cortex.
Key Words:
nuclear magnetic resonance, eye movements, plasticity
