Brain oscillations and synchrony in neurocognitive systems

Brain activity is strongly oscillatory: the collective firing of populations of neurons waxes and wanes in a rhythmic manner. The spatiotemporal and frequency-band characteristics of these oscillations may reflect how the brain organizes its activity, in a local as well as large scale manner. But how do brain oscillations relate to behavior and cognition? Can we understand psychological processes better by studying brain oscillations? This question was investigated in this thesis by means of several overarching topics. For example, I studied how humans combine auditory and visual sensory information when judging the passage of time. During these judgments, I observed strong inter-regional alpha-band (8-12 Hz) synchronization between visual and auditory processing regions. This is evidence that cross-modal integration may be happening at the level of the primary sensory regions, and not necessarily by some higher ("amodal") binding region. In addition, I investigated in multiple studies how theta-band (4-8 Hz) oscillations relate to various instances of cognitive control. For example, fast, impulsive performance errors were characterized by strong midfrontal theta dynamics, while slower errors due to attention lapses rather showed parieto-occipital alpha suppression. In addition, causally boosting theta oscillations in the brain through electrical stimulation, improved cognitively controlled behavior. Collectively, the studies that I present in this thesis elucidate the functional significance of different frequency bands in the instantiation of various neurocognitive mechanisms in the brain.