Humans human 165 motivation Motivation 129 female 105 male 100 adult 93 Female 80 Male 71 Adult 63 psychology 52 Article 50 young adult 49 controlled study 46 Young Adult 43 adolescent 42 Adolescent 41 article 40 major clinical study 34 physiology 34 human experiment 30 middle aged 30 Middle Aged 29 Reward 25 reward 25 Goals 24 questionnaire 21 decision making 18 aged 17 child 17