Rema V, Armstrong-James M, Jenkinson N, Ebner F F
National Brain Research Centre, Nainwal Mode, Manesar, Haryana 122050, India.
Neuroscience. 2006 Jun 30;140(2):659-72. doi: 10.1016/j.neuroscience.2006.02.043. Epub 2006 Apr 17.
Cortical sensory neurons adapt their response properties to use and disuse of peripheral receptors in their receptive field. Changes in synaptic strength can be generated in cortex by simply altering the balance of input activity, so that a persistent bias in activity levels modifies cortical receptive field properties. Such activity-dependent plasticity in cortical cell responses occurs in rat cortex when all but two whiskers are trimmed for a period of time at any age. The up-regulation of evoked responses to the intact whiskers is first seen within 24 h in the supragranular layers [Laminar comparison of somatosensory cortical plasticity. Science 265(5180):1885-1888] and continues until a new stable state is achieved [Experience-dependent plasticity in adult rat barrel cortex. Proc Natl Acad Sci U S A 90(5):2082-2086; Armstrong-James M, Diamond ME, Ebner FF (1994) An innocuous bias in whisker use in adult rat modifies receptive fields of barrel cortex neurons. J Neurosci 14:6978-6991]. These and many other results suggest that activity-dependent changes in cortical cell responses have an accumulation threshold that can be achieved more quickly by increasing the spike rate arising from the active region of the receptive field. Here we test the hypothesis that the rate of neuronal response change can be accelerated by placing the animals in a high activity environment after whisker trimming. Test stimuli reveal an highly significant receptive field bias in response to intact and trimmed whiskers in layer IV as well as in layers II-III neurons in only 15 h after whisker trimming. Layer IV barrel cells fail to show plasticity after 15-24 h in a standard cage environment, but produce a response bias when activity is elevated by the enriched environment. We conclude that elevated activity achieves the threshold for response modification more quickly, and this, in turn, accelerates the rate of receptive field plasticity.
皮层感觉神经元会根据其感受野中外周感受器的使用和停用情况来调整自身的反应特性。通过简单地改变输入活动的平衡，就可以在皮层中产生突触强度的变化，这样活动水平的持续偏差会改变皮层感受野特性。当在任何年龄将除两根之外的所有胡须修剪一段时间后，大鼠皮层中就会出现这种皮层细胞反应的活动依赖性可塑性。对完整胡须诱发反应的上调最早在24小时内出现在颗粒上层 [体感皮层可塑性的层间比较。《科学》265(5180):1885 - 1888]，并持续到达到新的稳定状态 [成年大鼠桶状皮层中经验依赖性可塑性。《美国国家科学院院刊》90(5):2082 - 2086；阿姆斯特朗 - 詹姆斯M、戴蒙德ME、埃布纳FF(1994)成年大鼠胡须使用中的无害偏差改变了桶状皮层神经元的感受野。《神经科学杂志》14:6978 - 6991]。这些以及许多其他结果表明，皮层细胞反应的活动依赖性变化有一个积累阈值，通过提高感受野活跃区域产生的放电率可以更快地达到这个阈值。在这里，我们检验这样一个假设，即胡须修剪后将动物置于高活动环境中可以加速神经元反应变化的速率。测试刺激显示，在胡须修剪仅15小时后，IV层以及II - III层神经元对完整和修剪胡须的反应中存在高度显著的感受野偏差。在标准笼养环境中，IV层桶状细胞在15 - 24小时后未显示出可塑性，但当丰富环境提高活动水平时会产生反应偏差。我们得出结论，活动水平升高能更快地达到反应改变的阈值，进而加速感受野可塑性的速率。
