Which Rhythms Reflect Bottom-Up and Top-Down Processing?

Top-down processing is how the mind uses our expectations, attentional focus, and other cognitive variables to adaptively influence bottom-up sensory processing. In this Chapter we summarize and review the main sources of evidence for how different neuronal oscillations contribute to top-down and bottom-up processing. We start with a historical and methodological overview with a focus on studies that have provided rich spatio-temporal dynamics to reveal the operations that underlie cognition. We then discuss four primary sources of evidence for how dynamics in the alpha/beta (8–30 Hz) and gamma (40–100 Hz) frequency bands map onto top-down and bottom-up processing, respectively. First, we discuss task manipulations that have isolated bottom-up and top-down processing. Second, we discuss studies that have measured cortical dynamics with laminar resolution. Third, we discuss studies of inter-areal directed connectivity. Fourth, we discuss causal manipulation studies. We end with a discussion of directions for future research to elucidate how top-down versus bottom-up communication is achieved in the brain.