T he observation that the mere activation of the idea of a behavioral act moves the human body without the person consciously deciding to take action has long been a topic of scientific interest (1-3). Initially, this ideomotor principle was used to explain extraordinary activities such as compliance under hypnosis, automatic writing, dowsing, and swinging pendulums. Lately, research on social cognition and neuroscience has revealed that seeing or reading about a behavior available in the individual's repertoire increases the tendency to perform it, which has been interpreted as a result of the common code that action concepts share with motor programs. Whereas activating the mental representation of behavior outside of awareness-that is, subliminal priming-indeed prepares people to initiate rapidly the corresponding behavior, an important issue recently addressed is how such subliminal priming effects may acquire an intrinsic motivational property in the sense that people mobilize additional resources and actually spend effort on a task (4). We studied the emergence of such unconscious motivation by examining how subliminal priming of the action concept of physical exertion causes people to spend effort.Building on research on the basic role of affective value in reward learning and motivation, we propose that the mechanism that turns subliminal priming of action concepts into motivation relies on the tagging of positive affect to the action concept (5). Specifically, we investigated that activating the behavior representation of exertion through subliminal priming prepares the execution of the corresponding behavior and that this priming actually motivates effortful behavior when that representation is coactivated with positively valenced stimuli that act as a reward signal. To test this, we subjected 42 participants to a priming task that enabled us to combine the subliminal priming of words representing exertion with briefly presented, although consciously visible positive words [Supporting Online Material (SOM) text]. Accordingly, three different conditions were created: a (control) condition in which only positive stimuli were presented, a (priming) condition in which exertion was subliminally primed but not directly paired with positive stimuli, and a (primingplus-reward) condition in which exertion was subliminally primed and immediately linked to positive stimuli.After the manipulations, we recorded handgrip force, which allowed us to differentiate between action preparation and motivation. Participants were instructed to squeeze a hand grip for 3.5 s when the word "squeeze" appeared on the screen. Results (Fig. 1) showed that participants in the priming and priming-plus-reward conditions started to squeeze earlier and increased their force faster than those in the control condition: The reaction time was shorter, and the initial slope toward the maximal force (rate of increase in applied force) was steeper in these two priming conditions. This faster initiation of the response to squeeze the hand grip ...