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Dania Abuleil, Daphne McCulloch, Benjamin Thompson; Indirect measures of visual cortex plasticity and GABA concentration are not correlated in adults with normal vision. Journal of Vision 2018;18(10):762. doi: 10.1167/18.10.762.
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Introduction Increases in visually-evoked potential (VEP) amplitude can be induced by rapid visual stimulation. This effect involves LTP mechanisms and provides an acute, objective measure of human visual cortex plasticity. Gamma-aminobutyric acid (GABA) may influence adult visual cortex plasticity. GABA concentration is inversely associated with alternation rate (AR) during binocular rivalry. Therefore, AR provides an indirect measure of GABA levels. Our aim was to test for an association between LTP and AR in young (18-40 years, n = 29) and older adults (60-80 years, n = 18). Two age groups were tested because GABA concentration changes across the lifespan. Methods Binocular rivalry was induced using orthogonal gratings viewed through anaglyphic glasses and ARs were averaged across 6 trials. LTP was assessed by comparing VEP amplitude for an onset/offset checkerboard stimulus (0.3 degree checksize, 4 degrees of visual angle) before and after 2 minutes of viewing the checkerboard presented at 9Hz. Pre and post VEPs were recorded for 3 minutes at a baseline frequency of 1Hz. Results ARs were significantly slower in older adults than young adults (t48=6.043, p< 0.001). LTP induction differed significantly between groups (F1=20.772, p< 0.001). VEP depotentiation (LTD) occurred in the young adult group (t28=3.444, p=0.002) vs. potentiation (LTP) for the older adult group (t17=-2.927, p=0.009). No correlation between AR and the change in VEP amplitude was observed for either group (p>0.05). Conclusion AR was not associated with VEP amplitude change following LTP induction. However, we did observe two unexpected effects. 1) Contrary to previous reports, visual cortex LTP could not be induced in younger adults, 2) greater LTP (higher visual cortex plasticity) occurred in the older group that had slower AR (higher visual cortex GABA concentration). Therefore, age substantially alters the response of the visual system to rivalrous stimuli and rapid visual stimulation.
Meeting abstract presented at VSS 2018
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