===== Event Boundaries =====

**Definition**:  
Event boundaries are **moments in time when the brain segments continuous experience into discrete units** called "events." These transitions typically occur at **changes in context**, such as shifts in location, characters, goals, or perceptual features during real-world or narrative experiences (e.g., movies or stories).

===== Characteristics =====

  * **Perceptual shifts**: Sudden changes in visual, auditory, or spatial context.
  * **Conceptual shifts**: Changes in characters' goals, social interactions, or narrative structure.
  * **Temporal markers**: Often correspond to natural pauses or breaks (e.g., scene cuts, silence, fade-outs).
  * **Detected by the brain**: Even without explicit instruction, observers show consistent segmentation of events.

===== Neural Correlates =====

  * **Hippocampus**: Exhibits increased activation at event boundaries, associated with memory encoding.
  * **Posterior medial cortex** (e.g., precuneus, retrosplenial cortex): Active during transitions, suggesting involvement in context updating.
  * **Default Mode Network (DMN)**: Modulated by narrative boundaries and self-referential processing.
  * **Ripple-like activity**: Intracranial EEG studies show increased ripple events around event boundaries, possibly reflecting mnemonic updating.

===== Functional Significance =====

  * **Memory formation**: Boundaries serve as anchors, organizing episodic memory into structured units.
  * **Prediction error**: Boundaries often coincide with violations of expectation, prompting neural updating.
  * **Narrative comprehension**: Helps maintain coherent models of ongoing events in naturalistic settings.

===== Experimental Paradigms =====

  * **Movie segmentation tasks**: Participants indicate when one meaningful event ends and another begins.
  * **fMRI and iEEG alignment**: Neural activity is time-locked to annotated event boundaries to study brain dynamics.
  * **Naturalistic stimuli**: Used increasingly to examine cognition in ecologically valid scenarios.

===== Clinical Relevance =====

  * Impaired segmentation is linked to **memory fragmentation**, especially in aging, schizophrenia, or brain injury.
  * Understanding event boundary processing may inform rehabilitation strategies for **episodic memory dysfunction**.