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The Journal of Neuroscience, January 28, 2009, 29(4):1006-1010; doi:10.1523/JNEUROSCI.3424-08.2009

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Brief Communications
Dynamical Response Properties of Neocortical Neuron Ensembles: Multiplicative versus Additive Noise

Clemens Boucsein,^1,2 Tom Tetzlaff,^1,3 Ralph Meier,^1,2 Ad Aertsen,^1,2 and Björn Naundorf⁴

¹Bernstein Center for Computational Neuroscience, and ²Neurobiology and Biophysics, Faculty of Biology, Albert Ludwigs University, D-79104 Freiburg, Germany, ³Institute of Mathematical Sciences and Technology, Norwegian University of Life Sciences, N-1430 Ås, Norway, and ⁴Max Planck Institute for Dynamics and Self-Organization, University of Göttingen, D-37073 Göttingen, Germany

Correspondence should be addressed to Dr. Clemens Boucsein, Faculty of Biology, Albert Ludwigs University, Schaenzlestrasse 1, D-79104 Freiburg, Germany. Email: Clemens.Boucsein@biologie.uni-freiburg.de

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.

Key words: transfer function; linear response; population rate; multiplicative noise; pyramidal cell; ensemble

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Received July 21, 2008; revised Dec. 12, 2008; accepted Dec. 14, 2008.

Correspondence should be addressed to Dr. Clemens Boucsein, Faculty of Biology, Albert Ludwigs University, Schaenzlestrasse 1, D-79104 Freiburg, Germany. Email: Clemens.Boucsein@biologie.uni-freiburg.de

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