Evidence of criticality at various levels of neuronal organization has accumulated over the past 2 decades. However, little is known of how criticality affects brain function, whether the critical state is always optimal for information processing, and whether the brain can change its operating point with regards to criticality so as to accommodate varying information processing requirements. Therefore, the aim of this thesis is to elucidate mechanisms that regulate brain criticality and to understand their impact on local and global information processing. We empirically validated that the brain can control the level of criticality via neuromodulation, with implications on perception. Then, we relied on computational modeling to gain full control on the parameters that determine criticality, and tested the implications of the level of criticality on two theories of brain function. Last, since excitation/inhibition balance is known to be a crucial determinant of criticality, which can vary across individuals, but also within subjects across time with neuromodulation, we developed a method to non-invasively estimate the functional E/I ratio.