特定方位的光栅识别学习不改变猫外膝体背核神经元的方位敏感性

Oriented grating discrimination learning does not improve orientation sensitivity of dLGN neurons of the cat

视觉信号识别训练可改变视觉通路神经元的可塑性, 其神经机制尚不清楚。已有少数研究显示, 动物(猴) 长时间进行特定方位的光栅识别学习后, 视皮层部分神经元对视觉刺激的反应表现出与学习任务相关的敏感性变化。这种敏感性变化是否亦存在于皮层下结构尚无报道。本实验训练两只成年猫分别进行水平和垂直方位的条形静止正弦光栅的识别以获得食物奖赏, 两只猫的行为识别能力逐渐提高, 4 个多月后识别的正确率达85%以上, 用与训练方位垂直的正弦光栅检测发现, 识别正确率明显下降。细胞外记录外膝体背核(Dorsal lat eral geniculate nucleus, dLGN) 神经元对不同方位正弦光栅刺激的反应显示, 与正常猫相比, 训练猫外膝体细胞的最优方位并未向着训练方位发生明显改变, 对于感受野位于中央区15度视角以内的细胞来说, 其方位选择性强度以及在训练方位的发放强度与正常猫无明显差异。以上结果表明, 猫对特定方位的光栅识别学习不改变外膝体神经元的方位敏感性, 其行为上方位识别特异性的提高可能与视皮层细胞的方位编码可塑性有关。

Practising visual signal discrimination can change neural plasticity in the visual pathway, the mechanism of which remains unknown. Several investigations have shown that after a long-term discrimination learning of specifically oriented gratings, the response of parts of neurons in the visual cortex of trained animals (monkeys) presented task-relevant sensitivity changes. So far, no investigation was carried out to determine whether these changes could take place in sub-cortical structures or not. In the present experiment, two adult cats were trained to discriminate respectively the horizontal and vertical static sinusoidal gratings for food reward. Performance of the two cats improved gradually and reached a percent correction above 85% after about 4 months of hard training. Testing with an orientation orthogonal to the trained orientation showed a significant reduction in correct performance for the two cats. Extracellularly recording the responses of dLGN (dorsal lateral geniculate nucleus) neurons to sinusoidal gratings with different orientations showed that preferred orientations of dLGN neurons in trained cats, compared with that in untrained cats, did not shift in favour of the trained orientation. For cells with receptive fields located within 15° visual acuity away from the foveae, trained cats showed no significant change in orientation bias and firing rate at trained orientation compared with untrained cats. All above indicate that oriented grating discrimination learning does not lead to a shift of orientation sensitivity for dLGN neurons in the cat. The specificity of performance improvement at trained orientation may be related to neural plasticity of orientation encoding in the visual cortex.