Max-Planck-Institut für empirische Ästhetik, ArtLab Foyer
The Westend Lectures on Brain and Cognition with Leon Deouell
Seeing the Big Picture: Hierarchy of Automatic Prediction
According to the predictive-coding framework the brain encodes regularities in the environment which are in turn used for predicting the input, and signaling deviations from this prediction. The mismatch response is taken as a paradigmatic example for such 'prediction error' signals produced automatically in response to unattended deviations from regularity. However, even for the simplest input, multiple predictions, sometimes contradicting, may be formed. I will discuss EEG and intracranial (ECOG) studies in humans, using auditory stimuli, and argue that temporal (auditory) and frontal cortices are both involved in the mismatch response, yet they reflect different predictions. Specifically, responses in the auditory cortex are dimension specific and reflect local probabilities on a short temporal scale, whereas frontal cortices are dimension-independent and reflect the global statistics of the input. Finally, I will show evidence that predictions are reflected not only in prediction-error signals, but also in anticipatory, proactive modulation of broadband high frequency local field potentials.
In a study involving intracranial recordings, five patients listened to trains of task-irrelevant tones in two conditions with randomly placed deviations (irregular condition) or with deviation every fifth stimulus (regular condition). We recorded ERPs as well as high frequency broadband (HFB) power modulation from multiple sites over temporal and prefrontal cortex, from grids of electrodes implanted for clinical purposes. Both temporal and frontal sites responded to deviations with an HFB increase. However, temporal sites responded to expected and unexpected deviations alike, whereas frontal sites responded exclusively to unexpected deviations. Furthermore, only prefrontal cortex showed anticipatory HFB power suppression prior to the onset of expected deviants, which correlated well with the post-stimulus suppression of response to expected deviations. Pre-stimulus HFB activity in the prefrontal cortex was also sensitive to the "hazard function" - the increasing likelihood of deviants following longer trains of standards in irregular conditions. These results indicate a hierarchy of predictions: auditory cortex creates mismatch response vis a vis short-range regularities, whereas the prefronal cortex encodes high level and temporally long-range regularities.