The Dynamic Brain

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Neuronal responses to identical stimuli exhibit significant variability, often previously labeled as "noise." At the single neuron level, interspike interval (ISI) histograms during spontaneous or stimulus-evoked activity show a Poisson distribution, suggesting that neurons have intrinsic firing variability. Traditional averaging techniques, such as post-stimulus time histograms (PSTH) and event-related potentials (ERPs), have been used based on the assumption of noise in neuronal responses. However, recent studies measuring the information content of single neuron spike trains indicate that substantial information can be encoded even amid trial-to-trial variability. Experiments involving multiple single-unit recordings suggest that variability once deemed noise may reflect broader changes in cellular response properties. This raises the intriguing possibility that variability in neuronal responses could contain meaningful information for the nervous system's processing. To explore how neurons collaborate for coherent behavior and its disruptions in disease, neuroscientists now record simultaneously from hundreds of neurons across different brain areas, analyzing network activities through interdependence measures like cross-correlation, phase synchronization, and spectral coherence. This work delves into neuronal variability from theoretical, experimental, and clinical angles.