What is emotional and arousal regulation primarily handled by?

The limbic system is primarily responsible for emotional and arousal regulation, making it the correct answer. This complex set of structures, located deep within the brain, plays a crucial role in controlling emotions, motivation, mood, and the formation of memories. Key components of the limbic system, such as the amygdala and hippocampus, are directly involved in processing emotional responses and are essential for the regulation of feelings like fear, pleasure, and aggression.

In contrast, the other options relate to different functions within the brain. The reptilian brain, often associated with basic survival instincts and reflexes, does not handle complex emotional regulation. The neocortex, which is involved in higher-level function such as reasoning and planning, processes more sophisticated thoughts rather than direct emotional regulation. Lastly, the primary motor cortex is responsible for initiating and controlling voluntary movements, which is quite different from managing emotions or arousal states. Thus, the limbic system stands out as the primary area tasked with these regulatory functions.