Avalanches and oscillations in the brain

Many biological systems present some collective behavior, that turns out not to be dependent on their specific details, and that provides them with some functional advantages, such as a trade-off between robustness (i.e. resilience to perturbation) and flexibility (i. e. responsiveness to environmental stimuli). For example, earthquakes and forest-fires are characterized by a dynamics that is similar to the one of neuronal avalanches that were found in 2003 by Beggs and Plenz. On the other hand, a vacuum tube radio generator, a pendulum clock, a firefly that emits light pulses, a contracting human heart are all active systems that taken apart, or being isolated, continue to oscillate in their own rhythms. The object of this thesis is to investigate those collective properties and to understand from which minimal ingredients they emerge in the barrel cortex and in newborns’ brains. In particular, it will be analyzed how these coherent structures change after the system is stimulated: respectively, the rat barrel cortex will be perturbed through controlled whisker stimulation, and newborns’ auditory cortex will be stimulated through the presentation of brief sentences in different languages. Following the work by Beggs and Plenz, neuronal avalanches across the layers of the barrel cortex will be analyzed; yet, not only during spontaneous activity but also after stimulation of the whisker. Already at this stage, the role of oscillations will be taken into account. Then, the collective activity of the barrel cortex will be analyzed from another perspective: from the point of view of the correlation length of the system. We will then analyze the role of oscillations and avalanches in the barrel cortex on a more recent dataset. The after-whisker oscillations will be studied, as well as their presence during spontaneous activity. Their functional role will be analyzed with a barrel cortex model, that will give insights on the way oscillations arise through a cortico-thalamic interplay. The results that we will find will also suggest an explanation for the coexistence of avalanches and oscillations in the studied system. Finally, some analysis on a different dataset, EEG recordings from newborns’s neural activity, that receive stimulations with sentences, are presented. We will study criticality and complexity of the neuronal oscillations of this dataset through the lens of the detrended fluctuations analysis method.