State-based versus reward-based motivation in younger and older adults
Cognitive Affective & Behavioral Neuroscience (2014) - Comment
pubmed: 24845527  doi: 10.3758/s13415-014-0293-8  issn: 1531-135x  issn: 1530-7026 

Darrell A. Worthy, Jessica A. Cooper, Kaileigh A. Byrne, Marissa A. Gorlick, W. Todd Maddox