Large Adam M, Vogler Nathan W, Mielo Samantha, Oswald Anne-Marie M
Department of Neuroscience, Center for the Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, PA 15260.
Department of Neuroscience, Center for the Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, PA 15260
Proc Natl Acad Sci U S A. 2016 Feb 23;113(8):2276-81. doi: 10.1073/pnas.1519295113. Epub 2016 Feb 8.
Throughout the brain, the recruitment of feedforward and recurrent inhibition shapes neural responses. However, disentangling the relative contributions of these often-overlapping cortical circuits is challenging. The piriform cortex provides an ideal system to address this issue because the interneurons responsible for feedforward and recurrent inhibition are anatomically segregated in layer (L) 1 and L2/3 respectively. Here we use a combination of optical and electrical activation of interneurons to profile the inhibitory input received by three classes of principal excitatory neuron in the anterior piriform cortex. In all classes, we find that L1 interneurons provide weaker inhibition than L2/3 interneurons. Nonetheless, feedforward inhibitory strength covaries with the amount of afferent excitation received by each class of principal neuron. In contrast, intracortical stimulation of L2/3 evokes strong inhibition that dominates recurrent excitation in all classes. Finally, we find that the relative contributions of feedforward and recurrent pathways differ between principal neuron classes. Specifically, L2 neurons receive more reliable afferent drive and less overall inhibition than L3 neurons. Alternatively, L3 neurons receive substantially more intracortical inhibition. These three features--balanced afferent drive, dominant recurrent inhibition, and differential recruitment by afferent vs. intracortical circuits, dependent on cell class--suggest mechanisms for olfactory processing that may extend to other sensory cortices.
在整个大脑中，前馈抑制和反馈抑制的募集塑造了神经反应。然而，区分这些经常重叠的皮质回路的相对贡献具有挑战性。梨状皮质提供了一个解决这个问题的理想系统，因为负责前馈抑制和反馈抑制的中间神经元在第1层（L1）和第2/3层（L2/3）在解剖学上是分开的。在这里，我们结合使用中间神经元的光学和电激活来描绘前梨状皮质中三类主要兴奋性神经元所接收的抑制性输入。在所有类别中，我们发现L1中间神经元提供的抑制比L2/3中间神经元弱。尽管如此，前馈抑制强度与每类主要神经元接收到的传入兴奋量共变。相比之下，对L2/3的皮质内刺激会引发强烈的抑制，在所有类别中这种抑制都主导着反馈兴奋。最后，我们发现前馈和反馈通路的相对贡献在主要神经元类别之间有所不同。具体而言，与L3神经元相比，L2神经元接收更可靠的传入驱动且总体抑制较少。或者说，L3神经元接收的皮质内抑制要多得多。这三个特征——平衡的传入驱动、占主导地位的反馈抑制以及传入与皮质内回路的差异募集（取决于细胞类别）——提示了嗅觉处理的机制，这些机制可能延伸到其他感觉皮质。
