Boucsein Clemens, Tetzlaff Tom, Meier Ralph, Aertsen Ad, Naundorf Björn
Bernstein Center for Computational Neuroscience, Faculty of Biology, Albert Ludwigs University, D-79104 Freiburg, Germany.
J Neurosci. 2009 Jan 28;29(4):1006-10. doi: 10.1523/JNEUROSCI.3424-08.2009.
To understand the mechanisms of fast information processing in the brain, it is necessary to determine how rapidly populations of neurons can respond to incoming stimuli in a noisy environment. Recently, it has been shown experimentally that an ensemble of neocortical neurons can track a time-varying input current in the presence of additive correlated noise very fast, up to frequencies of several hundred hertz. Modulations in the firing rate of presynaptic neuron populations affect, however, not only the mean but also the variance of the synaptic input to postsynaptic cells. It has been argued that such modulations of the noise intensity (multiplicative modulation) can be tracked much faster than modulations of the mean input current (additive modulation). Here, we compare the response characteristics of an ensemble of neocortical neurons for both modulation schemes. We injected sinusoidally modulated noisy currents (additive and multiplicative modulation) into layer V pyramidal neurons of the rat somatosensory cortex and measured the trial and ensemble-averaged spike responses for a wide range of stimulus frequencies. For both modulation paradigms, we observed low-pass behavior. The cutoff frequencies were markedly high, considerably higher than the average firing rates. We demonstrate that modulations in the variance can be tracked significantly faster than modulations in the mean input. Extremely fast stimuli (up to 1 kHz) can be reliably tracked, provided the stimulus amplitudes are sufficiently high.
为了解大脑中快速信息处理的机制，有必要确定神经元群体在有噪声的环境中对传入刺激的响应速度有多快。最近，实验表明，在存在加性相关噪声的情况下，新皮层神经元群体能够非常快速地跟踪时变输入电流，频率可达数百赫兹。然而，突触前神经元群体放电率的调制不仅会影响突触后细胞突触输入的均值，还会影响其方差。有人认为，这种噪声强度的调制（乘性调制）比平均输入电流的调制（加性调制）能被更快地跟踪。在此，我们比较了两种调制方案下新皮层神经元群体的响应特性。我们将正弦调制的噪声电流（加性和乘性调制）注入大鼠体感皮层的V层锥体神经元，并测量了广泛刺激频率范围内的单次试验和群体平均的尖峰响应。对于这两种调制范式，我们都观察到了低通行为。截止频率明显很高，大大高于平均放电率。我们证明，方差的调制比平均输入的调制能被显著更快地跟踪。只要刺激幅度足够高，就能可靠地跟踪极快的刺激（高达1千赫兹）。
