Beierlein Michael, Fall Christopher P, Rinzel John, Yuste Rafael
Department of Biological Sciences, Columbia University, New York, New York 10027, USA.
J Neurosci. 2002 Nov 15;22(22):9885-94. doi: 10.1523/JNEUROSCI.22-22-09885.2002.
Sensory information reaches the cortex via thalamocortical (TC) synapses in layer 4. Thalamic relay neurons that mediate information flow to cortex operate in two distinct modes, tonic and burst firing. Burst firing has been implicated in enhancing reliability of information flow between individual neurons. However, little is known about how local networks of neocortical neurons respond to different temporal patterns of TC activity. We studied cortical activity patterns evoked by stimulating TC afferents at different frequencies, using a combination of electrophysiology and calcium imaging in TC slices that allowed for the reconstruction of spatiotemporal activity with single-cell resolution. Stimulation of TC axons at low frequencies triggered action potentials in only a small number of layer 4 neurons. In contrast, brief high-frequency stimulus trains triggered widespread recurrent activity in populations of neurons in layer 4 and then spread into adjacent layers 2/3 and 5. Recurrent activity had a clear threshold, typically lasted 300 msec, and could be evoked repetitively at frequencies up to 0.5 Hz. Moreover, the spatial extent of recurrent activity was controlled by the TC pattern of activity. Recurrent activity triggered within the highly interconnected networks of layer 4 might act to selectively amplify and redistribute transient high-frequency TC inputs, filter out low-frequency inputs, and temporarily preserve a record of past sensory activity.
感觉信息通过第4层的丘脑皮质（TC）突触到达皮质。介导信息流向皮质的丘脑中继神经元以两种不同模式运作，即紧张性放电和爆发式放电。爆发式放电与提高单个神经元之间信息流的可靠性有关。然而，对于新皮质神经元的局部网络如何响应TC活动的不同时间模式，我们却知之甚少。我们结合使用电生理学和钙成像技术，在TC切片中以单细胞分辨率重建时空活动，研究了不同频率刺激TC传入纤维所诱发的皮质活动模式。低频刺激TC轴突仅在少数第4层神经元中触发动作电位。相反，短暂的高频刺激序列在第4层神经元群体中引发广泛的反复活动，然后扩散到相邻的第2/3层和第5层。反复活动有明显的阈值，通常持续300毫秒，并且可以以高达0.5赫兹的频率重复诱发。此外，反复活动的空间范围由TC活动模式控制。在第4层高度互连的网络中触发的反复活动可能起到选择性放大和重新分配短暂高频TC输入、过滤低频输入以及暂时保存过去感觉活动记录的作用。
