Thalamocortical control of feed-forward inhibition in awake somatosensory 'barrel' cortex.
Thalamocortical control of feed-forward inhibition in awake somatosensory 'barrel' cortex.
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DOI：
10.1098/rstb.2002.1156
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发表时间：
2002-12
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影响因子：
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通讯作者：
H. Swadlow
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作者：
H. Swadlow
皮层内抑制在形成感觉皮层感受野中起作用，并由前馈和反馈机制介导。前馈抑制是两个过程中较快的一个，由单突触丘脑皮层（TC）输入驱动的抑制性中间神经元产生。原则上，当TC输入较弱时，前馈抑制可以防止靶皮层神经元达到阈值。然而，要做到这一点，抑制性中间神经元必须在低阈值下对TC输入做出反应，并非常迅速地产生尖峰。一个强大的前馈抑制将锐化目标皮层神经元的调谐特性，和具有敏感和广泛调谐的感受野的中间神经元可以介导这一过程。在啮齿动物和兔子的躯体感觉（S1）“桶”皮层的第4层中发现了具有这些特性的疑似抑制性中间神经元（SIN）。这些interneurons缺乏方向的选择性，在大多数皮质棘神经元和腹侧基底TC传入，但更敏感的皮质棘神经元低幅度晶须位移。本文关注的是TC脉冲激活S1 SIN，并与这种激活的后果。在清醒的家兔中同时研究多个TC神经元和多个S1 SIN，并使用交叉相关方法来检查功能连接。结果表明，一个强大的，时间上精确的，动态的和高度收敛/发散的功能输入腹侧基底TC神经元的SIN的地形对齐的S1桶。而广泛汇集的收敛TC输入到SIN产生敏感和广泛调谐的抑制性感受野，强大的TC分歧到许多SIN产生急剧同步活动，这些元素。这种TC前馈抑制网络非常适合于提供对靶向棘神经元的快速、有效、灵敏和广泛调谐的抑制，其将抑制除了最佳前馈兴奋性输入之外的所有尖峰生成。
Intracortical inhibition plays a role in shaping sensory cortical receptive fields and is mediated by both feed-forward and feedback mechanisms. Feed-forward inhibition is the faster of the two processes, being generated by inhibitory interneurons driven by monosynaptic thalamocortical (TC) input. In principle, feed-forward inhibition can prevent targeted cortical neurons from ever reaching threshold when TC input is weak. To do so, however, inhibitory interneurons must respond to TC input at low thresholds and generate spikes very quickly. A powerful feed-forward inhibition would sharpen the tuning characteristics of targeted cortical neurons, and interneurons with sensitive and broadly tuned receptive fields could mediate this process. Suspected inhibitory interneurons (SINs) with precisely these properties are found in layer 4 of the somatosensory (S1) 'barrel' cortex of rodents and rabbits. These interneurons lack the directional selectivity seen in most cortical spiny neurons and in ventrobasal TC afferents, but are much more sensitive than cortical spiny neurons to low-amplitude whisker displacements. This paper is concerned with the activation of S1 SINs by TC impulses, and with the consequences of this activation. Multiple TC neurons and multiple S1 SINs were simultaneously studied in awake rabbits, and cross-correlation methods were used to examine functional connectivity. The results demonstrate a potent, temporally precise, dynamic and highly convergent/divergent functional input from ventrobasal TC neurons to SINs of the topographically aligned S1 barrel. Whereas the extensive pooling of convergent TC inputs onto SINs generates sensitive and broadly tuned inhibitory receptive fields, the potent TC divergence onto many SINs generates sharply synchronous activity among these elements. This TC feed-forward inhibitory network is well suited to provide a fast, potent, sensitive and broadly tuned inhibition of targeted spiny neurons that will suppress spike generation following all but the most optimal feed-forward excitatory inputs.