Declined contrast sensitivity of neurons along the visual pathway in aging cats.

Zhengchun Wang,Guangxing Li,Yifeng Zhou,Nini Yuan,Zhimo Yao,Zhen Liang

doi:10.3389/fnagi.2014.00163

Abstract

Changes in the visual cortex appear to mediate much of the visual degradation during normal aging. However, how aging affects different stages along the visual pathway is unclear. In the current study, the contrast response function, one of the most important properties of neurons from early visual areas to high brain areas, was systematically compared along the visual pathway, including the lateral geniculate nucleus (LGN), early visual cortices (A17 and A18), and posteromedial lateral suprasylvian cortex (PMLS, analog to the medial temporal area (MT) in monkeys) of young and old cats. We found that the effects of aging on the LGN were negligible, whereas those in the striate cortex were substantial, with even more severe degradation in the PMLS. Reduced contrast sensitivity of neurons in the three cortical areas was accompanied by enhanced maximal visual response, increased spontaneous activity, and decreased signal-to-noise ratio, while LGN neurons exhibited largely normal response properties. Our results suggested that there was a progressively greater effect of aging on neurons at successively higher stages in the visual pathway.

Highlights

Senescence is associated with a decline in many aspects of visual functions (Baracat and Marquie, 1992; Schefrin et al, 1999; Bennett et al, 2007)
Results demonstrated that CH and other response properties of lateral geniculate nucleus (LGN) neurons in old cats were relatively unchanged compared with young ones (Table 1 and Figure 1)
EFFECT OF AGING ON posteromedial lateral suprasylvian cortex (PMLS) NEURONS The results indicated significantly increased C50 values, elevated maximal visual responses and spontaneous activity, and decreased signal-to-noise ratio (SNR) of PMLS neurons in old cats when compared to young ones

Summary

Introduction

Senescence is associated with a decline in many aspects of visual functions (Baracat and Marquie, 1992; Schefrin et al, 1999; Bennett et al, 2007). The age-related degeneration of perception of higher-order stimuli (e.g., contrast-defined secondorder patterns) is significantly more pronounced, and can be detected much earlier than lower-order tasks (e.g., luminancedefined first-order stimuli) (Habak and Faubert, 2000; Tang and Zhou, 2009). These impairments cannot be solely due to optical changes or changes in the retina alone (Elliott et al, 1990; Owsley, 2011), and probably reflect age-related alterations occurring in the central nervous system, i.e., postretinal visual information processing (Higgins et al, 1988; Spear, 1993; Schmolesky et al, 2000). Examination of a series of brain areas along the visual pathway in the same experimental conditions would provide a more accurate picture of age-related changes

Methods

Results

Conclusion