Top-Down Versus Bottom-Up Processing in the Human Brain: Distinct Directional Influences Revealed by Integrating SOBI and Granger Causality

Top-down and bottom-up processing are two distinct yet highly interactive modes of neuronal activity underlying normal and abnormal human cognition. Here we characterize the dynamic processes that contribute to these two modes of cognitive operation. We used a blind source separation algorithm called second-order blind identification (SOBI [1]) to extract from high-density scalp EEG (128 channels) two components that index neuronal activity in two distinct local networks: one in the occipital lobe and one in the frontal lobe. We then applied Granger causality analysis to the SOBI-recovered neuronal signals from these two local networks to characterize feed-forward and feedback influences between them. With three repeated observations made at least one week apart, we show that feed-forward influence is dominated by alpha while feedback influence is dominated by theta band activity and that this directionselective dominance pattern is jointly modulated by situational familiarity and demand for visual processing.