What aspect of human function is primarily affected by serotonin?

Serotonin is a neurotransmitter that plays a crucial role in regulating mood and arousal, making it a significant factor in emotional well-being. It contributes to feelings of happiness and satisfaction, and imbalances in serotonin levels are often linked to mood disorders such as depression and anxiety. The enhancement or stabilization of mood is a key function of serotonin, as it helps to maintain emotional equilibrium and is involved in the modulation of various bodily functions associated with mood.

The other options, while related to human functions, are not primarily influenced by serotonin. Muscle contraction is predominantly regulated by neurotransmitters such as acetylcholine, memory formation involves numerous brain regions and chemical signals beyond serotonin, and movement coordination relies heavily on other neurotransmitters and systems, particularly those involving dopamine and motor control pathways. Understanding serotonin's primary focus on mood and arousal helps clarify its role in mental health and emotional regulation.