Final answer:
The cortical regions activated when thinking about a stimulus no longer present are located in the prefrontal cortex, which is crucial for working memory, executive functions, and recollection tasks.
Step-by-step explanation:
When thinking about a stimulus that is no longer present, cortical regions in your prefrontal cortex are activated. This area of the brain is essential for working memory and executive functions, which include organizing and representing information that isn't currently in the environment, focusing attention on goals, and inhibiting distractions.
The prefrontal cortex is involved in tasks that require recall and the processing of semantic information, as indicated by increased activation in various studies using brain scans such as PET scans.