We refer to this latter form of impulse as an ‘urge’. It relates to how much someone wants something, driven by its perceived value. Urges constitute an important part of human behavior, both in healthy everyday life and in psychiatric disorders. Yet there is a paucity of methods to objectively index urges in terms of strength, timing (dynamics) and control. While it is possible

to measure the strength of the urge in terms of response time, or number of items chosen/consumed, or subjective self-report (Raylu & Oei, 2004; Seibt et al., 2007; Wulfert et al., 2009), these behavioral measures do not provide information about the dynamic unfolding of the urge in real-time, nor are they suitable for measuring urge control. If an urge is stopped then there is nothing to observe behaviorally. We

aimed to develop a technique to measure urges by assuming they would ‘spill over’ into learn more the motor system. This assumption has a precedent. For example, it has been shown that action is more vigorous for stimuli with higher motivational value, and that this has its counterpart in increased blood oxygen level-dependent (BOLD) activation in the nucleus accumbens area (Talmi et al., 2008). A different study used functional magnetic resonance imaging (fMRI) and skin conductance to show that Venetoclax ic50 value modulates behavioral activation and BOLD signal in the pallidum even with subliminal stimuli (Pessiglione et al., 2007). Yet a limitation of these studies is

that the subject knows exactly which response to make, so the increased activation may also reflect motor execution rather than a purer measure of motivation to respond. Nor do these measures provide the sub-second resolution needed to separate the effects of motivation from those of execution. A different approach used transcranial magnetic stimulation (TMS) of the primary motor cortex to show that motor excitability (recorded from the hand) was modulated by an upcoming potential reward (Kapogiannis et al., 2008). However, that study required passive viewing without any action and, moreover, varied both reward value and Etomidate the probability of getting reward, thus making it unclear whether the increased motor excitability relates to urge per se rather than any of arousal, expectancy or uncertainty. We developed a novel approach to index urges in the motor system using TMS and concurrent electromyography. In Experiment 1 we used a realistic and previously validated food paradigm with hungry human participants (Hare et al., 2009). In Experiment 2 we used a similar paradigm with monetary rewards. We hypothesized that stimuli associated with stronger urges (for food or money) would lead to higher motor excitability. We aimed to show that this would be manifest even before the subject knew which motor response to make. We also aimed to clarify the within-trial timing of the effect and also to address whether the effect depends on making an action.