Nowak L G, Sanchez-Vives M V, McCormick D A
Section of Neurobiology, Yale University School of Medicine, New Hayen, CT 06510, USA.
Cereb Cortex. 1997 Sep;7(6):487-501. doi: 10.1093/cercor/7.6.487.
Cortical neurons in vivo respond to sensory stimuli with the generation of action potentials that can show a high degree of variability in both their number and timing with repeated presentations as wells as, on occasion, a high degree of synchronization with other cortical neurons, including in the gamma frequency range of 30-70 Hz. Here we examined whether or not this variability may arise from the intrinsic mechanisms of action potential generation in cortical regular spiking, fast spiking and intrinsic burst-generating neurons maintained in vitro. For this purpose, we performed intracellular recordings in slices of ferret visual cortex and activated these cells with the intracellular injection of various current waveforms. Some of these waveforms were derived from barrages of postsynaptic potentials evoked by visual stimulation recorded in vivo; others were artificially created and contained various amounts of gamma range fluctuations; finally, others consisted of swept-sinewave current (ZAP current) functions. Using such stimuli, we found that, as expected given the resistive and capacitive properties of cortical neurons, low frequencies have a larger effect on the membrane potential of cortical neurons than do higher frequencies. However, increasing the amount of gamma range fluctuations in a stimulus leads to more precise timing of action potentials. This suggests that different frequencies play different roles, low frequencies being efficient for depolarizing cells with high frequencies increasing the precision of action potential timing. In parallel to increases in temporal precision, the addition of higher frequency components increases the range of interspike intervals present in the action potential discharge. These results suggest that higher frequency components such as gamma range fluctuations may facilitate the generation of action potentials with a high temporal precision while at the same time exhibiting a high degree of variability in interspike intervals on single trials. This temporal precision may facilitate the use of temporal codes or the generation of precise synchronization for the transmission and analysis of information within cortical networks.
体内的皮质神经元对感觉刺激产生动作电位，在重复呈现时，动作电位的数量和时间都可能表现出高度的变异性，偶尔还会与其他皮质神经元高度同步，包括在30-70赫兹的伽马频率范围内。在这里，我们研究了这种变异性是否可能源于体外培养的皮质规则发放神经元、快速发放神经元和内在爆发性神经元动作电位产生的内在机制。为此，我们在雪貂视觉皮质切片中进行了细胞内记录，并用各种电流波形的细胞内注射激活这些细胞。其中一些波形来自体内记录的视觉刺激诱发的突触后电位阵；其他波形是人工创建的，包含不同数量的伽马范围波动；最后，其他波形由扫频正弦波电流（ZAP电流）函数组成。使用这些刺激，我们发现，鉴于皮质神经元的电阻和电容特性，低频对皮质神经元膜电位的影响比高频更大。然而，增加刺激中伽马范围波动的量会导致动作电位的时间更精确。这表明不同频率发挥不同作用，低频有效地使细胞去极化，高频则提高动作电位时间的精确性。与时间精确性的提高并行，添加更高频率成分会增加动作电位发放中峰峰间隔的范围。这些结果表明，诸如伽马范围波动等更高频率成分可能有助于产生具有高时间精确性的动作电位，同时在单次试验的峰峰间隔中表现出高度的变异性。这种时间精确性可能有助于使用时间编码或产生精确同步，以便在皮质网络内传输和分析信息。
