Liang Zhen, Chen Yue-Ming, Meng Xue, Wang Yi, Zhou Bao-Zhuo, Xie Ying-Ying, He Wen-Sheng
Department of Bio-Medical Engineering, Anhui Medical University, Hefei Anhui 230032, China.
Dongwuxue Yanjiu. 2012 Oct;33(5):498-502. doi: 10.3724/SP.J.1141.2012.05498.
The middle temporal area (MT/V5) plays an important role in motion processing. Neurons in this area have a strongly selective response to the moving direction of objects and as such, the selectivity of MT neurons was proposed to be a neural mechanism for the perception of motion. Our previous studies have found degradation in direction selectivity of MT neurons in old monkeys, but this direction selectivity was calculated during the whole response time and the results were not able to uncover the mechanism of motion perception over a time course. Furthermore, experiments have found that direction selectivity was enhanced by attention at a later stage. Therefore, the response should be excluded in experiments with anesthesia. To further characterize the neural mechanism over a time course, we investigated the age-related changes of direction selectivity in the early stage by comparing the proportions of direction selective MT cells in old and young macaque monkeys using in vivo single-cell recording techniques. Our results show that the proportion of early-stage-direction-selective cells is lower in old monkeys than in young monkeys, and that the early stage direction bias (esDB) of old MT cells decreased relative to young MT cells. Furthermore, the proportion of MT cells having strong early stage direction selectivity in old monkeys was decreased. Accordingly, the functional degradation in the early stage of MT cells may mediate perceptual declines of old primates in visual motion tasks.
颞中区（MT/V5）在运动处理中起着重要作用。该区域的神经元对物体的运动方向具有强烈的选择性反应，因此，MT神经元的选择性被认为是运动感知的一种神经机制。我们之前的研究发现，老年猴子MT神经元的方向选择性会下降，但这种方向选择性是在整个反应时间内计算得出的，结果无法揭示随时间推移的运动感知机制。此外，实验发现后期注意力会增强方向选择性。因此，在麻醉实验中应排除这种反应。为了进一步在时间进程中表征神经机制，我们使用体内单细胞记录技术，通过比较老年和幼年猕猴中方向选择性MT细胞的比例，研究了早期方向选择性的年龄相关变化。我们的结果表明，老年猴子中早期方向选择性细胞的比例低于幼年猴子，并且老年MT细胞的早期方向偏差（esDB）相对于幼年MT细胞有所降低。此外，老年猴子中具有强烈早期方向选择性的MT细胞比例也有所下降。因此，MT细胞早期的功能退化可能介导了老年灵长类动物在视觉运动任务中的感知能力下降。
