Harry Potter meets Markov: Neural event representation in the reading network during narrative processing

People segment ongoing information into meaningful mental representations known as events. Recent studies have found a spatio-temporal hierarchy in the event structure during movie watching and story listening. How the human brain segments stories while reading remains unclear. We examined event segmentation while reading Harry Potter using publicly available 3T fMRI data. To identify neural events, we employed a Hidden Markov Model (HMM) within six regions of interest (ROI) in the reading network. The ROIs included the inferior frontal gyrus (IFG), middle frontal gyrus (MFG), angular gyrus (AG), inferior frontal gyrus orbital (IFGorb), anterior temporal lobe (ATL), and posterior temporal lobe (PTL). These regions are also associated with DMN. The results revealed multiple timescales of events, with the IFG and AG representing shorter events, while the IFGorb, ATL, PTL and MFG represent relatively longer events. Boundaries of longer events were partially aligned within short events, suggesting a nested hierarchical event structure. Further comparisons identified associations between neural events and annotations from humans and ChatGPT (automated and less subjective segmentation) in the inferior frontal, temporal and parietal areas. Notably, the AG (a core region of the DMN and memory processing) and the IFG (relevant for language processing) exhibited stronger alignment with both sets of annotations. The findings suggest an important role of AG and IFG in event segmentation in reading. They also confirm the connection between the reading network and the DMN in event segmentation. This connection seems to be linked to the hierarchical processing of context-dependent semantic information during reading.