Reversal of cortical information flow during visual imagery as compared to visual perception

- We studied bottom-up and top-down connections during visual perception and imagery.
- A cortical occipito-parieto-frontal network was modeled from high-density EEG data.
- Our approach used both state-space Granger causality and dynamic causal modeling.
- Parieto-occipital directed connectivity reversed during imagery versus perception.
- This is the first quantitative demonstration of theorized connectivity reversal.

The role of bottom-up and top-down connections during visual perception and the formation of mental images was examined by analyzing high-density EEG recordings of brain activity using two state-of-the-art methods for assessing the directionality of cortical signal flow: state-space Granger causality and dynamic causal modeling. We quantified the directionality of signal flow in an occipito-parieto-frontal cortical network during perception of movie clips versus mental replay of the movies and free visual imagery. Both Granger causality and dynamic causal modeling analyses revealed an increased top-down signal flow in parieto-occipital cortices during mental imagery as compared to visual perception. These results are the first direct demonstration of a reversal of the predominant direction of cortical signal flow during mental imagery as compared to perception.