The neurotransmitters and are responsible for mood, attentiveness level, and other psychological states

The answer to your question is Dopamine and Serotonin. Dopamine is a neurotransmitter that affects our focus, drive, attention, memory and clear thinking. Elevation of dopamine levels leads to improvement in our mood, alertness, and libido. Serotonin, on the other hand, helps regulate a wide range of psychological and biological functions. It regulates psychological functions such as mood, anxiety, arousal, aggression, impulse control and thinking abilities. 

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the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.