Which neurotransmitter is known to be associated with feelings of anxiety, depression, and aggression?

The correct choice is serotonin, which is strongly linked to mood regulation and emotional well-being. Serotonin plays a crucial role in the brain's ability to manage anxiety, depression, and aggression. Low levels of serotonin are frequently associated with mood disorders such as depression and anxiety disorders, making it a key target for various antidepressant medications, particularly selective serotonin reuptake inhibitors (SSRIs).

The influence of serotonin on mood and emotional states is well-documented in numerous studies. Its role in stabilizing mood and fostering feelings of happiness or contentment underlines its importance in mental health. Therefore, understanding serotonin's effects is vital for those studying psychology and mental health, especially in relation to conditions characterized by anxiety and depression.