Alpha oscillations and traveling waves: Signatures of predictive coding?

Abstract

Predictive coding is a key mechanism to understand the computational processes underlying brain functioning: in a hierarchical network, higher levels predict the activity of lower levels, and the unexplained residuals (i.e., prediction errors) are passed back to higher layers. Because of its recursive nature, we wondered whether predictive coding could be related to brain oscillatory dynamics. First, we show that a simple 2-level predictive coding model of visual cortex, with physiological communication delays between levels, naturally gives rise to alpha-band rhythms, similar to experimental observations. Then, we demonstrate that a multilevel version of the same model can explain the occurrence of oscillatory traveling waves across levels, both forward (during visual stimulation) and backward (during rest). Remarkably, the predictions of our model are matched by the analysis of 2 independent electroencephalography (EEG) datasets, in which we observed oscillatory traveling waves in both directions.

DMT alters cortical travelling waves

“…Despite some initial debate 33 , it is now generally accepted that occipital visual regions become activated during visual imagery 34,35 . Placing these findings into the context of previous work demonstrating increased FW travelling waves during direct visual perception 16,17 , our present findings of increased FW waves under DMT correlating with visionary experiences lend significant support to the notion that DMT/ayahuasca and perhaps other psychedelics, engage the visual apparatus in a fashion that is consistent with actual exogenously driven visual perception. Future work could extend this insight to other apparently endogenous generated visionary experiences such as occur during dreaming and hallucinatory states.…”

“…The left column of figure 2A shows the amount of BW and FW waves in the 5 minutes preceding and following drug injection (either placebo or DMT). As previously reported 16 , during quiet closed-eyes restfulness a significant amount of BW waves spread from higher to lower regions (as confirmed by a Bayesian t-test against zero for both DMT and Placebo conditions, BFs10>>100), whereas no significant waves propagate in the opposite FW direction (Bayesian t-test against zero: BFs10<0.15).…”

“…We analyzed EEG signals recorded from a pool of participants who kept their eyes closed while receiving drug. Results revealed that compared with consistent eyes-closed conditions under placebo, eyes-closed DMT is associated with striking changes in cortical dynamics, which are remarkably similar to those observed during actual eyesopen visual stimulation 16,17 . Specifically, we observed a reduction in BW waves, and increase in FW ones, as well as an overall decrease in α band (8-12Hz) oscillatory frequencies 7 .…”

“…Quantifying travelling waves. We measure the waves' amount and direction with a method devised in our previous studies 16,17 . We slide a one-second time-window over the EEG signals (with 0.5s overlap).…”

“…Recent results showed that travelling waves can spread from occipital to frontal regions during visual perception, reflecting the forward bottom-up flow of information from lower to higher regions. Conversely, top-down propagation from higher to lower regions appears to predominate during quiet restfulness [16][17][18] .…”