Older Adults Exhibit Greater Visual Cortex Inhibition and Reduced Visual Cortex Plasticity Compared to Younger Adults

Abstract

Recent evidence indicates that inhibition within the visual cortex is greater in older than young adults. Increased inhibition has been associated with reduced visual cortex plasticity in animal models. We investigated whether age-related increases in human visual cortex inhibition occur in conjunction with reduced visual cortex plasticity. Visual cortex inhibition was measured psychophysically using binocular rivalry alternation rates (AR) for dichoptic gratings. Slower ARs are associated with a greater concentration of the inhibitory neurotransmitter GABA within the human visual cortex. Visual cortex plasticity was measured using an established paradigm for induction of long-term potentiation (LTP) -like increases in visually evoked potential (VEP) amplitude. Following rapid visual stimulation, greater increases in VEP amplitude indicate greater visual cortex plasticity. The study involved two groups; young (18–40 years, n = 29) and older adults (60–80 years, n = 18). VEPs were recorded for a 1 Hz onset/offset checkerboard stimulus before and after 9 Hz visual stimulation with the same stimulus. ARs were slower in older than young adults. In contrast to most previous studies, VEP amplitudes were significantly reduced following the rapid visual stimulation for young adults; older adult VEP amplitudes were unaffected. Our AR results replicate previous observations of increased visual cortex inhibition in the older adults. Rapid visual stimulation significantly altered VEP amplitude in young adults, albeit in the opposite direction than predicted. VEP amplitudes did not change in older adults suggesting an association between increased inhibition and reduced plasticity within the human visual cortex.

Differential Circuit Mechanisms of Young and Aged Visual Cortex in the Mammalian Brain

“…Previous studies have reported an overall decrease in GABA concentration during aging, which negatively influences the neural plasticity of visual cortex in old age [88]. A relatively slower amplitude response was observed in aged adults with increased levels of GABA-mediated visual cortex inhibition [87,88]. In response to rapid visual stimulation, young adults showed greater changes in visually evoked potential amplitude than aged individuals, suggesting that neural plasticity is higher at young age [88].…”

“…In response to rapid visual stimulation, young adults showed greater changes in visually evoked potential amplitude than aged individuals, suggesting that neural plasticity is higher at young age [88]. Aged adults do not exhibit any significant change in visually evoked potential amplitude in response to visual stimuli, as increased GABA-mediated inhibition is associated with lower amplitude response and is associated with reduced neural plasticity in V1 [88]. No significant change in visually evoked potential amplitudes in aged adults suggests a correlation between increased inhibition and reduced neural plasticity along aging.…”

“…Neural plasticity in the human visual cortex is greater during early developmental stages of childhood and gradually declines with age [87,88]. Previous studies have reported an overall decrease in GABA concentration during aging, which negatively influences the neural plasticity of visual cortex in old age [88]. A relatively slower amplitude response was observed in aged adults with increased levels of GABA-mediated visual cortex inhibition [87,88].…”

“…A relatively slower amplitude response was observed in aged adults with increased levels of GABA-mediated visual cortex inhibition [87,88]. In response to rapid visual stimulation, young adults showed greater changes in visually evoked potential amplitude than aged individuals, suggesting that neural plasticity is higher at young age [88]. Aged adults do not exhibit any significant change in visually evoked potential amplitude in response to visual stimuli, as increased GABA-mediated inhibition is associated with lower amplitude response and is associated with reduced neural plasticity in V1 [88].…”

The Defensive Activation theory: dreaming as a mechanism to prevent takeover of the visual cortex

“…For example, infants' brains are more plastic, and thus the competition for territory is even more critical. As an animal ages, the decrease in neuroplasticity makes cortical takeover increasingly difficult or impossible ( 21 ) , so the proportion of sleep time spent in REM should decrease with age. The data are consistent with this prediction: there is a clear and significant decrease in REM (as a percentage of total sleep time) across the lifespan ( 15 ) .…”