Guangxing Li

McGill University, Montréal, Quebec, Canada

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Publications (9)37.4 Total impact

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    ABSTRACT: Aged humans exhibit severe deficits in visual motion perception and contrast sensitivity under various levels of spatial and temporal modulation. Previous studies indicated that many of these deficits are probably mediated by the neural degradation of the central visual system. To clarify the neuronal response mechanisms underlying the visual degradation during aging, we examined the spatial and temporal frequency tuning properties of neurons from anesthetised and paralysed aged monkeys at the middle temporal area (area MT), which is downstream of the primary visual cortex in the visual processing pathway and thought to be critical for motion perception. We found that the preferred spatial and temporal frequencies, spatial resolution and high temporal frequency cutoff of area MT neurons were reduced in aged monkeys, and were accompanied by the broadened tuning width of spatial frequency, elevated spontaneous activity, and decreased signal-to-noise ratio. These results showed that, for neurons in area MT, aging significantly changed both the spatial and temporal frequency response tuning properties. Such evidence provides new insight into the changes occurring at the electrophysiological level that may be related to the aging-related visual deficits, especially in processing spatial and temporal information.
    European Journal of Neuroscience 06/2014; · 3.75 Impact Factor
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    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.
    Frontiers in Aging Neuroscience 01/2014; 6:163. · 5.20 Impact Factor
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    ABSTRACT: Chronic exposure to opiates leads to maladaptive changes in various functions of the mammalian brain, including properties of neuronal response in the visual pathway. In the present study, we used multibarreled microelectrodes to study the effects of electrophoretic application of γ-aminobutyric acid (GABA) or the GABAA receptor antagonist bicuculline on the properties of individual V1 neurons in cats which were chronically treated with morphine (MTCs) or saline (STCs). The results showed that the application of either GABA or bicuculline significantly altered spontaneous activity as well as orientation selectivity and signal-to-noise ratios of visually evoked responses in both MTCs and STCs. While administration of bicuculline exerted a much stronger effect on neuronal responses of V1 neurons of the STCs, administration of GABA resulted in improved visual function mainly in MTCs. Most importantly, GABA-treated cells in area V1 of the MTCs displayed similar responses to those in STCs. These results are consistent with the idea that: 1) there is a decrease in GABA-mediated inhibition in area V1 of cats exposed chronically to morphine, and 2) this decrease contributes strongly to the apparent degradation of neuronal function observed in animals exposed chronically to morphine.
    Neuroscience 03/2013; · 3.12 Impact Factor
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    ABSTRACT: The visual system is hierarchically organized between and within areas. Previous studies have found that aging affects different visual areas in a progressive manner, e.g. more degradation occurs in the primary visual cortex (V1) than in the dorsal lateral geniculate nucleus (dLGN), and more in the secondary visual (V2) and middle temporal (MT) visual areas than in V1. In view of these findings, we hypothesize that higher levels within the visual information hierarchy are affected more severely by aging. Hierarchies exist not only between visual areas but also within areas (e.g. V1, has a simple to complex cell hierarchy). We expected that a similar pattern of ageing effects should be found within a given visual area. To study this question, primary visual cortex is a good candidate because there is good evidence for the simple to complex cell hierarchy. In this paper, we applied single unit recording techniques to study the visual response properties of V1 simple and complex cells in young and old monkeys in vivo. We found that the orientation and direction selectivity of complex cells were significantly degraded in old monkeys, while those of simple cells were relatively spared from the effects of aging. These findings are consistent with the hypothesis that higher hierarchical levels in the visual system, both between and within areas, may be affected more severely by aging.
    Brain research 06/2012; 1470:17-23. · 2.46 Impact Factor
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    Bo Chen, Jing Xia, Guangxing Li, Yifeng Zhou
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    ABSTRACT: Physiological and behavioral studies have demonstrated that a number of visual functions such as visual acuity, contrast sensitivity, and motion perception can be impaired by acute alcohol exposure. The orientation- and direction-selective responses of cells in primary visual cortex are thought to participate in the perception of form and motion. To investigate how orientation selectivity and direction selectivity of neurons are influenced by acute alcohol exposure in vivo, we used the extracellular single-unit recording technique to examine the response properties of neurons in primary visual cortex (A17) of adult cats. We found that alcohol reduces spontaneous activity, visual evoked unit responses, the signal-to-noise ratio, and orientation selectivity of A17 cells. In addition, small but detectable changes in both the preferred orientation/direction and the bandwidth of the orientation tuning curve of strongly orientation-biased A17 cells were observed after acute alcohol administration. Our findings may provide physiological evidence for some alcohol-related deficits in visual function observed in behavioral studies.
    Toxicology and Applied Pharmacology 03/2010; · 3.98 Impact Factor
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    ABSTRACT: Visual function declines with age. Much of the decline may result from functional degradation in central visual areas. To investigate the physiological mechanisms underlying visual function declines during normal aging, we compared the response variability of cells in primary visual cortex (V1) and middle temporal visual area (MT) in young adult and very old macaque monkeys using single-neuron in vivo electrophysiology. We found that mean response and response variability in both V1 and MT of old monkeys are significantly higher than in young monkeys. And response-to-noise ratio in old monkeys is significantly lower than in young ones. The results are consistent with an age-related degradation of inhibitory intracortical circuits. The neural changes described here could contribute to declines in visual function during senescence.
    Brain research 05/2009; 1274:21-7. · 2.46 Impact Factor
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    ABSTRACT: Human perception of speed declines with age. Much of the decline is probably mediated by changes in the middle temporal (MT) area, an extrastriate area whose neural activity is linked to the perception of speed. In the present study, we used random-dot patterns to study the effects of aging on speed-tuning curves in cortical area MT of macaque visual cortex. Our results provide evidence for a significant degradation of speed selectivity in MT. Cells in old animals preferred lower speeds than did those in young animals. Response modulation and discriminative capacity for speed in old monkeys were also significantly weaker than those in young ones. Concurrently, MT cells in old monkeys showed increased baseline responses, peak responses and response variability, and these changes were accompanied by decreased signal-to-noise ratios. We also found that speed discrimination thresholds in old animals were higher than in young ones. The foregoing neural changes may mediate the declines in visual motion perception that occur during senescence.
    Cerebral Cortex 12/2008; 19(9):1957-67. · 8.31 Impact Factor
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    ABSTRACT: Morphine exposure may have a negative effect on the receptive field properties of neurons in primary visual cortex of cats. The present experiment used morphological methods in order to investigate whether chronic morphine treatment also affects dendritic characters of these neurons. According to the Sholl analysis and dendritic branch order analysis, we obtained the dendritic length and calculated the spine density on dendrites of the pyramidal neurons in layer III and the spiny stellate neurons in layer IV. The results showed that morphine exposure induced significant decreases in the total dendritic length and spine density on both pyramidal and spiny stellate neurons. The further branch order analysis revealed that spine density was decreased at every (first to fourth) branch order of dendrites of pyramidal and spiny stellate neurons. Decrease in dendritic length of the pyramidal neurons was observed only at the fourth branch order, while the spiny stellate neurons had shorter dendrite at the second and third branch order. These findings may underlie the degradation of receptive field properties of the primary visual cortex neurons following chronic morphine exposure.
    Brain research bulletin 09/2008; 77(2-3):77-83. · 2.18 Impact Factor
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    ABSTRACT: The ability to accurately perceive the direction and speed of moving objects declines during normal aging. This is likely due to functional degradation of cortical neurons. Most neurons in the primate middle temporal area (MT) are direction-selective and their activity is closely linked to the perception of coherent motion. We investigated the mechanisms that underlie this age-related decline by comparing the proportions of direction-selective MT cells in old and young macaque monkeys, using in vivo single-cell recording techniques. Our results showed that the proportion of such cells was lower in old than in young monkeys. Moreover, one type of direction-sensitive cells, pattern cells, was especially sensitive to aging and was affected more severely than another class, component cells. We also found that direction selectivity was affected more severely in MT than in V1 of senescent monkeys. Thus, the functional degradation of MT and V1 cells may mediate perceptual decline in visual motion tasks in old primates.
    Neurobiology of aging 08/2008; 31(5):863-73. · 5.94 Impact Factor

Publication Stats

76 Citations
37.40 Total Impact Points

Institutions

  • 2013–2014
    • McGill University
      • Division of Ophthalmology
      Montréal, Quebec, Canada
  • 2009–2014
    • University of Science and Technology of China
      • School of Life Sciences
      Luchow, Anhui Sheng, China
  • 2012
    • Anhui Medical University
      Luchow, Anhui Sheng, China
  • 2010
    • Chinese Academy of Sciences
      Peping, Beijing, China