Motor learning depends on plastic reorganization of neural networks within the primary motor cortex (M1). In the circuitry of M1, integration and processing of afferent inputs is executed by pyramidal neurons of layer II/III. Thus, an involvement of these layer II/III pyramids in learning-induced changes is highly plausible. We therefore analyzed dendritic plasticity in layer II/III pyramidal cells on Golgi-Cox silver-impregnated sections after training of a forelimb reaching task. Based on their location within layer II/III, neurons were assigned to either a superficial or a deep population. After training, morphological changes occurred in both superficial and deep layer II/III pyramids. Overall, a decrease in dendritic length could be observed. In detail, superficial cells showed a significant reduction in the length of the apical dendrite after training ended in contrast to deep layer II/III pyramids, where dendritic length initially remained stable. Both types of neurons showed a transient increment in complexity of the distal apical dendrite 30 days after training. Findings were different in basal dendrites: length and complexity continuously decreased in superficial and deep layer II/III pyramids. Spine density increased in apical and basal dendrites of both superficial and deep layer II/III neurons, likely an effect of ageing that occurred independently from motor learning. This increase in spine density was accompanied with a morphological change towards stubby- and mushroom-like spines. Thus, profound but delayed changes occurred within the dendritic compartment of layer II/III pyramidal cells.

运动学习取决于初级运动皮层（M1）中神经网络的塑性重组。在M1的电路中，传入输入的集成和处理由第II / III层的锥体神经元执行。因此，这些II / III层金字塔参与学习引起的变化是非常合理的。因此，我们在训练前肢到达任务后，在高尔基-科克斯银浸渍的切片上分析了II / III层锥体细胞中的树突可塑性。根据它们在II / III层中的位置，神经元被分配给浅表或深层人口。训练后，II / III浅层金字塔和深层金字塔均发生了形态变化。总体而言，可以观察到树突长度的减少。详细，与深层II / III金字塔相反，树突长度最初保持稳定，而训练结束后，浅表细胞显示出顶端树突的长度显着减少。训练后30天，两种类型的神经元均显示远端根尖树突的复杂性短暂增加。基部树突的发现不同：II / III表层和深层金字塔的长度和复杂性不断降低。浅层和深层II / III神经元的根部和基底树突的脊柱密度增加，这可能是独立于运动学习而发生的衰老影响。脊柱密度的增加伴随着向粗短和蘑菇状棘的形态变化。从而，