Final answer:
Low levels of serotonin are associated with increased aggression, extraversion, and attention-seeking behaviors.
Step-by-step explanation:
The neurotransmitter associated with behaviors such as aggression, extraversion, and attention seeking when at low levels is serotonin (option 2). Serotonin, also known as 5-hydroxytryptamine or 5-HT, plays a critical role in various body systems, including the central nervous system (CNS). It is implicated in a wide range of psychological functions, including mood regulation, appetite, and cognition. Low levels of serotonin are commonly linked to mental health conditions such as depression, and can also influence personality traits and behaviors like aggression and impulsivity. This neurotransmitter's expansive influence on the brain and behavior is due to its extensive network of projections throughout the CNS, affecting various regions related to mood and cognition.