How does the brain support script comprehension? A study of executive processes and semantic knowledge in dementia

The neuropsychological substrate of scripts, routines which guide much of human behavior, is unclear. We propose a model of script comprehension characterized by the interaction of semantic knowledge for script content, and executive resources that organize this knowledge into goal directed behavior. We examined these neuropsychological components by asking participants with Alzheimer's disease (AD) and frontotemporal dementia (behavioral disorder/dysexecutive syndrome (BDD) and semantic dementia (SD) subtypes), to judge the coherence of four-phrase scripts. The BDD group detected significantly fewer sequencing errors than semantic errors; the AD and SD groups detected these errors with equal frequency. Independent semantic measures predicted both semantic and sequencing script errors, while executive measures predicted sequencing errors only. Findings support a multi-component model of script comprehension.