Intracellular, In Vivo, Dynamics of Thalamocortical Synapses in Visual Cortex
Intracellular, In Vivo, Dynamics of Thalamocortical Synapses in Visual Cortex
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DOI：
10.1523/jneurosci.3370-16.2017
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发表时间：
2017-05
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通讯作者：
Madineh Sedigh-Sarvestani;L. Vigeland;Ivan Fernandez-Lamo;M. M. Taylor-M.;Larry A. Palmer;D. Contreras
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文献类型：
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作者：
Madineh Sedigh-Sarvestani;L. Vigeland;Ivan Fernandez-Lamo;M. M. Taylor-M.;Larry A. Palmer;D. Contreras
对猫视觉系统中丘脑皮层回路的研究，对我们理解感觉编码至关重要。然而，丘脑皮质突触的特性仍然知之甚少。我们使用配对记录，在外侧膝状体核（LGN）和初级视觉皮层（V1），提供第一个在体内表征的感觉驱动的丘脑皮层电位V1。我们的特点是幅度的EPSPs小于以前报道的体外。与之前的研究结果一致，只有当它们的感受野（RF）重叠时才能发现连接的LGN-V1对，并且连接的概率随着RF重叠和响应相似性的程度急剧增加。然而，令人惊讶的是，我们发现EPSP幅度和RF或响应的相似性之间没有关系，这表明不同的连接模型的皮质内和丘脑皮层电路。假定的兴奋性规则尖峰（RS）和抑制性快速尖峰（FS）V1细胞具有相似的EPSP特征，表明在视觉系统中，前馈兴奋和抑制由丘脑以相等的强度驱动。与躯体感觉皮层的观察结果相似，FS V1细胞从LGN接收的特异性输入较少。最后，V1中的方向调谐不是从单个突触前LGN细胞遗传的，这表明它必须完全来自所有突触前LGN细胞的组合输入。我们的研究结果有助于破译早期的视觉编码电路，并在提供生理约束的视觉系统的计算模型的直接效用。为了理解大脑如何编码视觉环境，我们必须了解视觉信号在大脑不同区域之间的传输。因此，了解突触动力学对我们理解感觉编码至关重要。本研究提供了在一个完整的动物视觉丘脑和视觉皮层之间的视觉诱发突触电位的第一个特征。为了记录这些电位，我们同时记录了初级视皮层输入层的突触前丘脑细胞的细胞外电位和突触后皮层细胞的细胞内电位。我们在体内的突触电位的特性不同意先前的研究结果在体外。这项研究将增加我们对丘脑皮层回路的理解，并将改善视觉编码的计算模型。
Seminal studies of the thalamocortical circuit in the visual system of the cat have been central to our understanding of sensory encoding. However, thalamocortical synaptic properties remain poorly understood. We used paired recordings, in the lateral geniculate nucleus (LGN) and primary visual cortex (V1), to provide the first in vivo characterization of sensory-driven thalamocortical potentials in V1. The amplitudes of EPSPs we characterized were smaller than those previously reported in vitro. Consistent with prior findings, connected LGN-V1 pairs were only found when their receptive fields (RFs) overlapped, and the probability of connection increased steeply with degree of RF overlap and response similarity. However, surprisingly, we found no relationship between EPSP amplitudes and the similarity of RFs or responses, suggesting different connectivity models for intracortical and thalamocortical circuits. Putative excitatory regular-spiking (RS) and inhibitory fast-spiking (FS) V1 cells had similar EPSP characteristics, showing that in the visual system, feedforward excitation and inhibition are driven with equal strength by the thalamus. Similar to observations in the somatosensory cortex, FS V1 cells received less specific input from LGN. Finally, orientation tuning in V1 was not inherited from single presynaptic LGN cells, suggesting that it must emerge exclusively from the combined input of all presynaptic LGN cells. Our results help to decipher early visual encoding circuits and have immediate utility in providing physiological constraints to computational models of the visual system. SIGNIFICANCE STATEMENT To understand how the brain encodes the visual environment, we must understand the transfer of visual signals between various regions of the brain. Therefore, understanding synaptic dynamics is critical to our understanding of sensory encoding. This study provides the first characterization of visually evoked synaptic potentials between the visual thalamus and visual cortex in an intact animal. To record these potentials, we simultaneously recorded the extracellular potential of presynaptic thalamic cells and the intracellular potential of postsynaptic cortical cells in input layers of primary visual cortex. Our characterization of synaptic potentials in vivo disagreed with prior findings in vitro. This study will increase our understanding of thalamocortical circuits and will improve computational models of visual encoding.