Joachimsthaler Bettina, Brugger Dominik, Skodras Angelos, Schwarz Cornelius
Werner Reichardt Center for Integrative Neuroscience, Systems Neuroscience, Hertie Institute for Clinical Brain Research, Department of Cognitive Neurology, Graduate School of Neural and Behavioural Science, and.
Werner Reichardt Center for Integrative Neuroscience, Systems Neuroscience, Hertie Institute for Clinical Brain Research, Department of Cognitive Neurology.
J Neurosci. 2015 Mar 4;35(9):3772-81. doi: 10.1523/JNEUROSCI.2043-14.2015.
Classical conditioning that involves mnemonic processing, that is, a "trace" period between conditioned and unconditioned stimulus, requires awareness of the association to be formed and is considered a simple model paradigm for declarative learning. Barrel cortex, the whisker representation of primary somatosensory cortex, is required for the learning of a tactile variant of trace eyeblink conditioning (TTEBC) and undergoes distinct map plasticity during learning. To investigate the cellular mechanism underpinning TTEBC and concurrent map plasticity, we used two-photon imaging of dendritic spines in barrel cortex of awake mice while being conditioned. Monitoring layer 5 neurons' apical dendrites in layer 1, we show that one cellular expression of barrel cortex plasticity is a substantial spine count reduction of ∼15% of the dendritic spines present before learning. The number of eliminated spines and their time of elimination are tightly related to the learning success. Moreover, spine plasticity is highly specific for the principal barrel column receiving the main signals from the stimulated vibrissa. Spines located in other columns, even those directly adjacent to the principal column, are unaffected. Because layer 1 spines integrate signals from associative thalamocortical circuits, their column-specific elimination suggests that this spine plasticity may be the result of an association of top-down signals relevant for declarative learning and spatially precise ascending tactile signals.
涉及记忆加工的经典条件作用，即条件刺激和非条件刺激之间的“痕迹”期，需要对即将形成的关联有所意识，并且被认为是陈述性学习的一种简单模型范式。桶状皮层是初级体感皮层中对触须的表征，是学习痕迹性眨眼条件反射（TTEBC）的触觉变体所必需的，并且在学习过程中会经历独特的图谱可塑性变化。为了研究支撑TTEBC及同时发生的图谱可塑性的细胞机制，我们在清醒小鼠接受条件刺激时，对其桶状皮层中的树突棘进行了双光子成像。通过监测第1层中第5层神经元的顶端树突，我们发现桶状皮层可塑性的一种细胞表现是，学习前存在的树突棘数量大幅减少了约15%。被消除的树突棘数量及其消除时间与学习的成功紧密相关。此外，树突棘可塑性对于接收来自受刺激触须主要信号的主要桶状柱具有高度特异性。位于其他柱中的树突棘，即使是那些与主要柱直接相邻的树突棘，也未受影响。由于第1层中的树突棘整合来自联合丘脑皮质回路的信号，它们的柱特异性消除表明，这种树突棘可塑性可能是与陈述性学习相关的自上而下信号和空间精确的上行触觉信号关联的结果。
